Harmonics and Harmonics limit

Harmonics and Harmonics limit

     Harmonics stand for the unwanted AC signals or disturbances in the AC supply. In technically speaking, the fundamental AC component (e.g. 200 Hz) in the main supply comprises of 2,3,4.. times that of fundamental frequency signals (400Hz, 600Hz, 800 Hz...). The fundamental AC component is normally a pure sinusoidal signal. The Harmonic component's magnitude will be of less in amplitude compared with fundamental.

 

Fundamental and harmonic components (courtesy: online source)

Source of harmonics:

     When the non linear loads such as UPS, chargers, Computers etc. are connected with the main supply, harmonics are generated. 

Effects of harmonics:

    Due to harmonics the power losses in the line increase, poor power factor etc.

Harmonic limits:

 Voltage harmonics i.e. THD level should be < 5%

  for current harmonics the THD level should be <8%

Otherwise the Electricity board may impart penalty for the amount of harmonics generated.

What is Electrical shock? How much our body withstand with electricity? How to protect ourself from earth leakage current?

Electric shock and its prevention

We are very often or rarely sense electric shock. Then a question arises technically , What is Electrical shock? How much our body withstand with electricity?
In Practical, when we are in contact with a live electric wire or touching an electrical equipment with leakage current, a current flow in our body, then we sense the shock.

What is the safe limit of this current?
there are 5 conditions, if the current flow persist in our body and the current limits is 
1) if the current is < 2 mA(Milli Ampere), it is insensible, safe
2) if the current is 2 mA to 10 mA, it is sensible, Let go current and Harmless
3) if the current is10mA to 25 mA, Muscular Contraction occur.(Sensing the shock)
4)  if the current is 25 mA to 50 mA, Ventricular Fibrillation occur, Immediate attention is required, within 20 minutes, we have to give defibrillator to active our heart functioning.
5) > 50 mA - fatal.

How to protect ourself from earth leakage current?
1. Earthing is necessary and must for the electrical appliances used in our home.
2. Now a days ELCB ( Earth Leakage Circuit Breaker) is available in the market, which can be installed  in our house wiring along with other Switchgear. It breaks the current if the earth current is >30 mA range.ELCB will be tripped off automatically, whenever the current crosses the safe limit.

ELCB (Illustration purpose only)

Solar Net Metering

Solar Net metering

As the national electrical power demand increases, alternate energy sources play a vital role to meet out some of the energy crises. In particular, the Solar PV system’s growth is very rapid.

Net meter is a bidirectional energy meter which indicates the energy usage by a consumer and excess energy produced by the consumer and exported to the utility grid.

In a grid connected Solar PV system, the excess energy generated can be exported to the utility grid. The net meter tracks the difference of excess energy fed back to the grid and the energy consumed by the consumer.

There are two conditions,

1. If the solar energy generated units is less than the load , then the net meter runs forward, the consumer has to pay the utility company
2. If the solar energy generated units are greater than the load, then the net meter runs backward, the consumer will be credited for excess energy.

The net metering usage and its policy differ from state to state. The tariff also differs. There will be an agreement between the consumer and the utility grid company.

 Merits:

1.      As the consumer is credited for excess energy, there will be financial benefit.

2.      As the system is grid connected, no need of battery storage, its cost involved and free from maintenance.

3.      No need of two meters separately for measuring energy consumption and excess energy exported to the utility grid.

Solar MPPT Concept

Solar MPPT Concept

The usage of solar power is gaining momentum everywhere in the World in order to meet the Power Demand and also for a Pollution free World.    Though solar power is available plenty on earth, its conversion into electrical energy by using Solar panels are very common and very meager due to its low conversion in efficiency. So, it is essential to extract maximum solar power from sun by using solar panels.  

It is time for the Undergraduate / Post graduate students to undertake Solar related projects for Efficient and effective way of extracting solar power.

 

MPPT stands for Maximum Power Point Tracking. This algorithm is most predominantly used in extracting Solar power.

There are mainly two types of solar energy extraction.
1. Mechanical tracking
2. Electrical tracing using at the converter/ inverter stage.

   In Mechanical tracking, the solar panel is tilted towards the solar directions and maximum power is harvested.

  In Electrical tracking, MPPT algorithm is used in the converter / inverter stage in the solar power conversion systems by appropriately controlling the On/Off time of switching in the  converter / inverters. Compared with first method, where mechanical control has been a drawback, in the second method, maximum power can be obtained by appropriately controlling the output voltage of solar panel. 

Solenoid valve control

Solenoid valves are normally used in engineering projects where water or liquid or gas flow controls are needed. I would like to describe some of its basics, features and applications in this article.

A solenoid valve is an electromechanical valve to control the flow of liquid or gas. The valve can be controlled by passing electrical current through a solenoid. There are two practical cases for control. One control is a two-port valve where the flow is switched on or off.  In the second case, a three-port valve is used in which the outflow has been switched between the two outlet ports. Multiple solenoid valves can also be used together on a manifold. Solenoid valves are often used as control elements in fluids/gas. Their main works are to shut/close off, release, dose, distribute or mix fluids. 

Solenoids features are
* very fast and safe switching,
* high reliability,
* long service life,
* good medium compatibility of the materials used,
* low control power and compact design.
Most of the applications use the plunger-type actuator and the other types are pivoted-armature actuators and rocker actuators.
 

Description about Solenoid valve: 

A solenoid valve consists of  two parts. They are solenoid and the valve. The solenoid part converts electrical energy into mechanical energy which is used for opening or closing the valves mechanically. Solenoid valves are normally metal seals or rubber seals, and have electrical interfaces to allow for controlling. A spring is  used to hold the valve opened or closed while the valve is not activated. In solenoid valves, particularly few cases, the solenoid acts directly over the main valve. Others use a small, complete solenoid valve, known as a pilot, to actuate a larger valve. While the second type is actually a solenoid valve combined with a pneumatically actuated valve, they are sold and packaged as a single unit referred to as a solenoid valve. Piloted valves consumes very less power for controlling, however, they are very slower. Piloted solenoids usually need full power at all times to open and stay open, where a direct acting solenoid may only need full power for a short period of time to open it, and only low power to hold it. 

Applications: 

Solenoid valves are used in 

* fluid power pneumatic and hydraulic systems, to control cylinders, fluid power motors or larger industrial valves. 

* solenoid valves with an automatic controller are used in automatic irrigation sprinkler systems. 

* solenoid valves are used to control water entry to the machine in domestic washing machines and dishwashers. 

* In the paintball industry, solenoid valves are usually referred to simply as "solenoids." They are commonly used to control a larger valve used to control the propellant (usually compressed air or CO2). 

* In the industry, "solenoid" may also refer to an electromechanical solenoid commonly used to actuate a sear.

Working of a PLC

WORKING OF PLC 

Most of the Engineering projects use PLC as heart of the project for control. PLC stands for Programmable Logic Controller. This article gives a overview of PLC and its working.

 

Basis of a PLC function is continual scanning of a program, under scanning we mean running through all conditions within a guaranteed period. Scanning process has three basic steps: Step 1: Testing input status. First, a PLC checks each of the inputs with intention to see which one of them has status ON or OFF. In other words, it checks whether a sensor, or a switch etc. connected with an input is activated or not. Information that processor thus obtains through this step is stored in memory in order to be used in the following step. Step2: Program execution. Here a PLC executes a program, instructed by instruction. Based on a program and based on a status of that input ad obtained in the preceding step, an appropriate action is taken. This reaction can be defined as activation of a certain output, or results can be put off and stored in memory to be retrieved later in the following step. Step 3: Checkup and correction of output status. Finally, a PLC checks up output status and adjust as it is needed. Change is performed based on the input status that had been read during the first step, and based on the results of program execution in step 2. Following the execution of step 3 PLC returns to the beginning of this cycle and continually repeats these steps. Scanning time is defined by the time needed to perform these three steps, and sometimes it is an important program feature. 

LADDER DIAGRAM Programmable controllers are generally programmed in ladder diagram (or “relay diagram”) which is nothing but a symbolic representation of electric circuits. Symbols were selected that actually looked similar to schematic symbols of electric devices, and this has made it much easier for electricians to switch to programming PLC controllers. Electrician who has never seen a PLC can understand a ladder diagram. 

NORMALLY OPEN AND NORMALLY CLOSED CONTACTS Since we frequently meet with concepts “normally open” and “normally closed” in industrial environment, it is important to know them. Both terms apply to words such as contacts, Inputs, outputs etc., (all combinations have the same meaning whether we are talking about input, output, contact or something else). Principle is quite simple, normally open switch won’t conduct electricity until it is pressed sown, and normally closed switch will conduct electricity will conduct electricity until it is pressed. Good examples for both situations are the doorbell and a house alarm. If a normally closed switch is selected, bell will work continually until someone pushed the switch. By pushing a switch, contacts are open and the flow of electricity towards the bell is interrupted. Of course, system so designed would not in any case suit the owner of the house. A better choice would certainly be a normally open switch. This way bell wouldn’t work until someone pushed the switch button and thus informed of his or her presence at the entrance. Home alarm system is an example of an application of a normally closed witch. Let’s suppose that the alarm system is intended for surveillance of the front door to the house. One of the ways to “wire” the house would be to install a normally open switch from each door to the alarm itself (precisely as with a bell switch). Then, if the door was opened, this would close the switch, and an alarm would be activated. This system could work, but there would be some problems with this too. Let’s suppose that switch is not working, that a wire is somehow disconnected or a switch is broken etc., (there are many ways in which this system could be dysfunctional). The real trouble is that a home owner would not know that a system was out of order. A burglar could open the door, a switch would not work, and the alarm would not be activated. Obviously, this isn’t a good way to set up this system. System should be set up in such a way so the alarm is activated by a burglar, but also by its own dysfunction, of if any of the components stopped working. (A house owner would certainly want to know if a system was dysfunctional). Having these things in mind, it is far better to use a switch with normally closed contacts which will detect an unauthorized entrance (opened door interrupts the flow of electricity and this signal is used to activate a sound signal), or failure on the system such as disconnected wire. These considerations are even more important in industrial environment where a failure could cause injury at work. One such example where outputs with normally closed contacts are used is a safety wall with trimming machines. If the wall doors open, switch affects the output with normally closed contacts and interrupts a supply circuit. This stops the normally closed contacts and interrupts a supply circuit. This stops the machine and prevents an injury. Concepts normally open and normally closed can apply to sensors as well. Sensors are used to sense the presence of physical objects, measure some dimension of some amount. For instance, one type of sensors can used to detect presence of box on an industry transfer belt. Other types can be used to measure physical dimensions such as heat etc., still most sensors are of a switch type. Their output is in status ON or OFF depending on what the sensor “feels”. Let’s take for instance a sensor made feel metal when a metal object passes by the sensor. For this purpose, a sensor with a normally open or a normally closed contact at the output could be used. If it were necessary to inform a PLC each time an object passed by the sensor, a sensor with a normally open should be selected. Sensor output would set off only if a metal object were placed right before the sensor. A sensor would turn off after the object has passed. PLC could then calculate how many times a normally open contact was set off at the sensor output, and would thus know how may metal objects passed by the sensor. Concepts normally open and normally closed contact ought to be clarified and explained in detail in the example of a PLC controller input and output. The easiest way to explain them is in the example of a relay. 

PROGRAMMING THE PLC PLC controller can be reprogrammed through a computer (usual way), but also through manual programmers (consoles). This practically means that each PLC controller can be programmed through a computer if you have the software needed for programming. Today’s transmission computers are ideal for reprogramming a PLC in factory itself. This is of great importance to the industry. Once the system is corrected, it is also important to tread the right program in to a PLC again. It is also good to check from time to time whether program in a PLC has not changed. This helps to avoid hazardous situations in factory room (some automakers have established communication networks which regularly check programs in PLC to ensure execution only of good programs).Almost every program for programming a PLC possess various useful options such as: forced switching on and off the system inputs/ outputs (I/O lines), program follow up in real time as well as define failures and malfunctions. Programmer can add remarks, names of input or output devices and comments that can be useful when finding errors, or with system maintenance. Adding comments and remarks enables any technician to quote precisely part numbers if replacements would be needed. This would speed up a repair of any problems that can come up due to bad parts. The old way such that a person who developed a system had protection on the program, so that nobody aside from this person could understand how it was done. Correctly documented ladder diagram allows any technician understand thoroughly how the system functions.

GPS Module GP810

GPS Module GP810

GP 810 Pin diagram

The GP 810 receiver board is based on the high performance GP 810 receiver architecture. This 810 receiver is ideally suited for applications that require easy replacement for Trimble Lassen LP and where the state of the art GP performance including fast TTFF even in extreme temperature is required. The GP 810 receiver offers user configurable, low power consumption with three different operational modes. 

Full navigation, Idle Mode and Sleep Mode can be customized to perfectly meet the requirements of each specific GPS application. The performance regarding sensitivity and very fast TTFF makes it applicable even for extremely demanding applications and environments with full industrial temperature range. The receiver supports the basic GPS functionality plus support for versatile control for sleep state and even the Data Logger to store position information to the internal non-volatile Flash memory. The I/O includes also power supply, ground, accurate 1 PPS output for timing applications and Power Mode Control input. Nominal power supply is +3.3V and typical current consumption is 52mA. All navigational data is stored in non-volatile 8 Mbit Flash memory meaning that no external back-up battery is required. The antenna connector is a MCX jack, which provides also the active antenna bias supply. The module supports optionally the Antenna Bias Supervisor, which detects a faulty condition, either Open or Short state and sends a respective message to the host.

Thermistor with OPAMP control circuit

Thermistor with OPAMP control circuit

 

Thermistor with LM324 OPAMP

A thermistor is a type of resistor used to measure temperature changes, relying on the change in its resistance with changing temperature. Thermistor is a combination of the words thermal and resistor. The Thermistor was first invented by Samuel Ruben in 1930.

If we assume that the relationship between resistance and temperature is linear (i.e. we make a first-order approximation), then we can say that: 

ΔR = Kδt 

Where ΔR = change in resistance ΔT = change in temperature k = first-order temperature coefficient of resistance 

Thermistors can be classified into two types depending on the sign of k. If k is positive, the resistance increases with increasing temperature, and the device is called a positive temperature coefficient (PTC) thermistor, Posistor. If k is negative, the resistance decreases with increasing temperature, and the device is called a negative temperature coefficient (NTC) thermistor. Resistors that are not thermistors are designed to have the smallest possible k, so that their resistance remains almost constant over a wide temperature range. 

Circuit Description: 

In this circuit the thermistor is used to measure the temperature. Thermistor is nothing but temperature sensitive resistor. There are two type of thermistor available such as positive temperature co-efficient and negative temperature co- efficient. Here we are using negative temperature co-efficient in which the resistance value is decreased when the temperature is increased. Here the thermistor is connected with resister bridge network. The bridge terminals are connected to inverting and non-inverting input terminals of comparator. 

The comparator is constructed by LM 324 operational amplifier. The LM 324 consist of four independent, high gains, internally frequency compensated operational amplifier which were designed specifically to operate from a single power supply over a wide voltage range. The first stage is a comparator in which the variable voltage due to thermistor is given to inverting input terminal and reference voltage is given to non-inverting input terminal.

Initially the reference voltage is set to room temperature level so the output of the comparator is zero. When the temperature is increased above the room temperature level, the thermistor resistance is decreased so variable voltage is given to comparator. Now the comparator delivered the error voltage at the output. Then the error voltage is given to next stage of preamplifier.

Here the input error voltage is amplified then the amplified voltage is given to next stage of gain amplifier. In this amplifier the variable resistor is connected as feedback resistor. The feedback resistor is adjusted to get desired gain. Then the AC components in the output are filtered with the help of capacitors. Then output voltage is given to final stage of DC voltage follower through this the output voltage is given to ADC or other circuit.

Digital to Analog Converter DAC 0800

Digital to Analog Converter : DAC 0800

Digital to Analog Converter(DAC 0800) with Current to Voltage converter(LM741)

In electronics, a digital-to-analog converter (DAC or D-to-A) is a device for converting a digital (usually binary) code to an analog signal (current, voltage or electric charge). Digital-to-analog converters are interfaces between the abstract digital world and analog real life. An analog-to-digital converter (ADC) performs the reverse operation. A DAC usually only deals with pulse-code modulation (PCM)-encoded signals. The job of converting various compressed forms of signals into PCM is left to codecs. Basic Operation: The DAC fundamentally converts finite-precision numbers (usually fixed-point binary numbers) into a physical quantity, usually an electrical voltage. 

Normally the output voltage is a linear function of the input number. Usually these numbers are updated at uniform sampling intervals and can be thought of as numbers obtained from a sampling process. These numbers are written to the DAC, sometimes along with a clock signal that causes each number to be latched in sequence, at which time the DAC output voltage changes rapidly from the previous value to the value represented by the currently latched number. The effect of this is that the output voltage is held in time at the current value until the next input number is latched resulting in a piecewise constant output. This is equivalently a zero-order hold operation and has an effect on the frequency response of the reconstructed signal. 

Basic Operation: The DAC fundamentally converts finite-precision numbers (usually fixed-point binary numbers) into a physical quantity, usually an electrical voltage. Normally the output voltage is a linear function of the input number. Usually these numbers are updated at uniform sampling intervals and can be thought of as numbers obtained from a sampling process. These numbers are written to the DAC, sometimes along with a clock signal that causes each number to be latched in sequence, at which time the DAC output voltage changes rapidly from the previous value to the value represented by the currently latched number. The effect of this is that the output voltage is held in time at the current value until the next input number is latched resulting in a piecewise constant output. This is equivalently a zero-order hold operation and has an effect on the frequency response of the reconstructed signal. The fact that practical DACs do not output a sequence of dirac impulses (that, if ideally low-pass filtered, result in the original signal before sampling) but instead output a sequence of piecewise constant values or rectangular pulses, means that there is an inherent effect of the zero-order hold on the effective frequency response of the DAC resulting in a mild roll-off of gain at the higher frequencies (a 3.9224 Db loss at the Nyquist frequency). 

This zero-order hold effect is a consequence of the hold action of the DAC and is not due to the sample and hold that might precede a conventional analog to digital converter as is often misunderstood. DAC0800 The DAC0800 series are monolithic 8 bit high speed current output digital to analog faturing typical setting times of 100ns. When used as a multiplying DAC, monotonic performance over a 40 to 1 refeence current range is possible. The DAC0800 series also features high complemementary current output to allow diferential output voltages of 20 Vp-p with simple resistor loads. The reference to full scale current matching of better than l LAB elimanates the need for full scale trims in most application while the nonlinearities of better than 0.1 over temperature minimize system error accumulations. 

The noise immune inputs of the DAC0800 series wil accepet TTL levels with the logic thershold pin grounded. Channging the Vlc potential will allow direct interface to other logic families. The pefrormance and characteriststics of the device are essentially unchanged over the full 4.5v to 18v power supply range power dissipation is only 33mvw with +5v supplies and is independent of the logic input states. The output of the DAC is current signal. So it is given to current voltage converter which is constructed by the LM 741 operational amplifier. Finally the anlaog voltage is given to Triac or SCR control circuit.

PROXIMITY SENSORs

PROXIMITY SENSOR

A proximity sensor detects an object when the object approaches within the detection boundary of the sensor. Proximity sensors are used in various facets of manufacturing for detecting the approach of metal objects. 

Various types of proximity sensors are used for detecting the presence or absence of an object. The design of a proximity sensor can be based on a number of principles of operation, some examples include: variable reluctance, eddy current loss, saturated core, and Hall Effect. Depending on the principle of operation, each type of sensor will have different performance levels for sensing different types of objects. 

Common types of non-contact proximity sensors include inductive proximity sensors, capacitive proximity sensors, ultrasonic proximity sensors, and photoelectric sensors. Hall-effect sensorsdetect a change in a polarity of a magnetic field. 

Variable reluctance sensors typically include a U-type core and coils wound around the core legs. Inductive proximity sensors have a lossy resonant circuit (oscillator) at the input side whose loss resistance can be changed by the proximity of an electrically conductive medium. 

An electrical capacitance proximity sensor converts a variation in electrostatic capacitance between a detecting electrode and a ground electrode caused by approaching the nearby object into a variation in an oscillation frequency, transforms or linearizes the oscillation frequency into a direct current voltage, and compares the direct current voltage with a predetermined threshold value to detect the nearby object. 

Ultrasonic sensing systems provide a much more efficient and effective method of longer range detection. These sensors require the use of a transducer to produce ultrasonic signals. 

Eddy-current proximity sensors are well known and operate on the principle that the impedance of an ac-excited electrical coil is subject to change as the coil is brought in close proximity to a metallic object. 

Proximity sensors often are employed in manufacturing industries in which the sensors are exposed to harsh environmental conditions. Inductive proximity sensors are used in automation engineering to define operating states in automating plants, production systems and process engineering plants.

Magnetic proximity detectors are commonly used on ski lifts and tramways for detecting a derope condition of the steel cable used as a haul line or haul rope. 

Proximity sensors are widely used in the automotive industry to automate the control of power accessories. For instance, proximity sensors are often used in power window controllers to detect the presence of obstructions in the window frame when the window pane is being directed to the closed position.

IC ULN 2803 driver circuit

IC ULN 2803 driver circuit

Logic diagramm

A ULN2803 is an Integrated Circuit (IC) chip with a High Voltage/High Current Darlington Transistor Array. It allows you to interface TTL signals. A TTL signal operates from 0-5V, with everything between 0.0 and 0.8V considered "low" or off, and 2.2 to 5.0V being considered "high" or on. The maximum power available on a TTL signal depends on the type, but generally does not exceed 25mW (~5mA @ 5V), so it is not useful for providing power to something like a relay coil. Computers and other electronic devices frequently generate TTL signals. On the output side the ULN2803 is generally rated at 50V/500mA, so if can operate small loads directly. 

Alternatively, it is frequently used to power the coil of one or more relays, which in turn allow even higher voltages/currents to be controlled by the low level signal. In electrical terms, the ULN2803 uses the low level (TTL) signal to switch on/turn off the higher voltage/current signal on the output side. The ULN2803 comes in an 18-pin IC configuration and includes eight (8) transistors. Pins 1-8 receive the low level signals; pin 9 is grounded (for the low level signal reference). Pin 10 is the common on the high side and would generally be connected to the positive of the voltage you are applying to the relay coil. Pins 11-18 are the outputs (Pin 1 drives Pin 18, Pin 2 drives 17, etc.).

The ULN2803 is a small integrated circuit that contains 8 transistor driver channels. Each channel has an input to a resistor connected to the base of a transistor and a 1 amp open collector output capable of handling up to about 30volts .Each of the collectors has a reverse biased diode connected to a common Vcc pin that provides inductive spike protection. Typical uses are for micro-processor interfaces to relays, lamps, solenoids and small motors. A 2803 with a set of relays is a simple and effective way of switching mains voltages for example.

Driver Features 

• TTL, DTL, PMOS, or CMOS Compatible Inputs 

• Output Current to 500 mA 

• Output Voltage to 95 V 

• Transient-Protected Outputs 

• Dual In-Line Package or Wide-Body Small-Outline Package 

Relay Vs Switch

A relay is an electrically operated switch. Current flowing through the coil of the relay creates a magnetic field which attracts a lever and changes the switch contacts. The coil current can be on or off so relays have two switch positions and they are double throw (changeover) switches. 

Relays allow one circuit to switch a second circuit which can be completely separate from the first. For example a low voltage battery circuit can use a relay to switch a 230V AC mains circuit. There is no electrical connection inside the relay between the two circuits; the link is magnetic and mechanical. The coil of a relay passes a relatively large current, typically 30mA for a 12V relay, but it can be as much as 100mA for relays designed to operate from lower voltages. 

Most ICs (chips) cannot provide this current and a transistor is usually used to amplify the small IC current to the larger value required for the relay coil. The maximum output current for the popular 555 timer IC is 200mA so these devices can supply relay coils directly without amplification. 

Relays are usually SPDT or DPDT but they can have many more sets of switch contacts, for example relays with 4 sets of changeover contacts are readily available. For further information about switch contacts and the terms used to describe them please see the page on switches. Most relays are designed for PCB mounting but you can solder wires directly to the pins providing you take care to avoid melting the plastic case of the relay. The supplier's catalogue should show you the relay's connections. The coil will be obvious and it may be connected either way round. Relay coils produce brief high voltage 'spikes' when they are switched off and this can destroy transistors and ICs in the circuit. To prevent damage you must connect a protection diode across the relay coil. The animated picture shows a working relay with its coil and switch contacts.

You can see a lever on the left being attracted by magnetism when the coil is switched on. This lever moves the switch contacts. There is one set of contacts (SPDT) in the foreground and another behind them, making the relay DPDT. 

The relay's switch connections are usually labeled COM, NC and NO: 

• COM = Common, always connect to this,it is the moving part of the switch. 

• NC = Normally Closed, 

COM is connected to this when the relay coil is off.

• NO = Normally Open, COM is connected to this when the relay coil is on. 

• Connect to COM and NO if you want the switched circuit to be on when the relay coil is on. 

• Connect to COM and NC if you want the switched circuit to be on when the relay coil is off. 

 Choosing a relay You need to consider several features when choosing a relay: 

1. Physical size and pin arrangement If you are choosing a relay for an existing PCB you will need to ensure that its dimensions and pin arrangement are suitable. You should find this information in the supplier's catalogue. 

2. Coil voltage The relay's coil voltage rating and resistance must suit the circuit powering the relay coil. Many relays have a coil rated for a 12V supply but 5V and 24V relays are also readily available. Some relays operate perfectly well with a supply voltage which is a little lower than their rated value. 

3. Coil resistance The circuit must be able to supply the current required by the relay coil. You can use Ohm's law to calculate the current: Relay coil current = supply voltage coil resistance 

4. For example: A 12V supply relay with a coil resistance of 400 passes a current of 30mA. This is OK for a 555 timer IC (maximum output current 200mA), but it is too much for most ICs and they will require a transistor to amplify the current. 

5. Switch ratings (voltage and current) The relay's switch contacts must be suitable for the circuit they are to control. You will need to check the voltage and current ratings. Note that the voltage rating is usually higher for AC, for example: "5A at 24V DC or 125V AC". 

6. Switch contact arrangement (SPDT, DPDT etc) Most relays are SPDT or DPDT which are often described as "single pole changeover" (SPCO) or "double pole changeover" (DPCO). For further information please see the page on switches. 

Protection diodes for relays Transistors and ICs (chips) must be protected from the brief high voltage 'spike' produced when the relay coil is switched off. The diagram shows how a signal diode (e.g. 1N4148) is connected across the relay coil to provide this protection. Note that the diode is connected 'backwards' so that it will normally not conduct. Conduction only occurs when the relay coil is switched off, at this moment current tries to continue flowing through the coil and it is harmlessly diverted through the diode. Without the diode no current could flow and the coil would produce a damaging high voltage 'spike' in its attempt to keep the current flowing. 

Advantages of relays: • Relays can switch AC and DC, transistors can only switch DC. • Relays can switch high voltages, transistors cannot. • Relays are a better choice for switching large currents (> 5A). • Relays can switch many contacts at once.

Disadvantages of relays: • Relays are bulkier than transistors for switching small currents. • Relays cannot switch rapidly (except reed relays), transistors can switch many times per second. • Relays use more power due to the current flowing through their coil. • Relays require more current than many chips can provide, so a low power transistor may be needed to switch the current for the relay's coil.

LIQUID CRYSTAL DISPLAY 

Liquid crystal cell displays (LCDs) are used in similar applications where LEDs are used. LCD displays are common in Engineering applications and play a vital role.  These applications are display of numeric and alphanumeric characters in dot matrix and segmental displays. Now a days Computer monitors and TV, Watches and advertisements  use  LCD technology for display. LCD display produces high quality images and thinner compared with CRT technologies. The basic idea behind the working of LCD is given here. 

LCDs are of two types: 

I. Dynamic scattering type 

II. Field effect type 

The construction of a dynamic scattering liquid crystal cell:

The liquid crystal material may be one of the several components, which exhibit optical properties of a crystal though they remain in liquid form. Liquid crystal is layered between glass sheets with transparent electrodes deposited on the inside faces. When a potential is applied across the cell, charge carriers flowing through the liquid disrupt the molecular alignment and produce turbulence. When the liquid is not activated, it is transparent. When the liquid is activated the molecular turbulance causes light to be scattered in all directions and the cell appeas to be bright.This phenomenon is called dyanamic scattering. 

source of image: Wikipedia

The construction of a field effect liquid crystal display 

This is similar to that of the dynamic scattering type,with the exception that two thin polarizing optical filters are placed at the inside of each glass sheet. The liquid crystal material in the field effect cell is also of different type from employed in the dynamic scattering cell. The material used is twisted nemayic type and actually twists the light passing through the cell when the latter is not energised. i. Transmittive type ii. Reflective type In the transmittive type cell, both glass sheets are transparent, so that light from a rear source is scattered in the forward direction when the cell is activated. In reflective type cell has a reflecting surface on one side of glass sheets. The incident light on the front surface of the cell is dynamically scattered by an activated cell. Both types of cells appear quite bright when activated even under ambient light conditions. The liquid crystals are light reflectors are transmitters and therefore they consume small amounts of energy (unlike light generators). 

The seven segment display, the current is about 25 micro Amps for dynamic scattering cells and 300micro amps for field effect cells. Unlike LEDs which can work on d.c. the LCDs require a.c. voltage supply. A typical voltage supply to dynamic scattering LCD is 30v peak to peak with 50 Hz

Analog to Digital Converter module

Analog to Digital Converter module

   Analog to Digital converter modules are used in Micro controller based projects where the analog signals are required to be converted into digital signal for further processing in Micro controller. The integrated chip used for this purpose is 0809 ADC. This post describe briefly the PIN diagram, block diagram and details of this specified chip here.

Pin Diagram

Circuit Diagram of ADC 0809

The ADC totally consists of 28 pins with 8 inputs and 8 outputs.The output from the filter is given to pin 26 of ADC 0809 shown in the figure above.The address channels A, B, C are grounded so that channel 1 is enabled. The digitized output from the converter is given to port 0 of micro controller. The control signals from the ADC are given to port 2 of the Microcontroller. This circuit follows the principle of successive approximation method and when the start of conversion goes high, it marks the beginning of the process and high end of conversion marks the end of it.The two capaciors 10F and 100F acts as filter. The filter capacitors in the circuit remove the low and high frequency noises. The LED is used to check the proper functioning of the circuit.

RF transmitter and Receiver modules are available in chip which can be effectively embedded with engineering projects.

These devices are simple pass-through integrated circuits. Meaning, you set up your baud-rate (as long as its within an acceptable range of whatever pair of devices you are using), and then start sending bytes to the transmitter. Quite simply, it just sends your data out the transmitter and the receiver grabs it, acting as if you had a wired serial connection between them, minus the wire!  The following PIN diagram shows the details of TLP 434,434A, 916A chips. The input/output units, antennas are integrated in this chip.

RF Transmitter

RF Receiver

MAX 232 and RS-232

MAX232 protocol:

The MAX232 is an integrated circuit that converts signals from an RS-232 serial port to signals suitable for use in TTL compatible digital logic circuits. The MAX232 is a dual driver/receiver and typically converts the RX, TX, CTS and RTS signals. The drivers provide RS-232 voltage level outputs (approx. ± 7.5 V) from a single + 5 V supply via on-chip charge pumps and external capacitors. This makes it useful for implementing RS-232 in devices that otherwise do not need any voltages outside the 0 V to + 5 V range, as power supply design does not need to be made more complicated just for driving the RS-232 in this case. The receivers reduce RS-232 inputs (which may be as high as ± 25 V), to standard 5 V TTL levels. These receivers have a typical threshold of 1.3 V, and a typical hysteresis of 0.5 V. It is helpful to understand what occurs to the voltage levels. When a MAX232 IC receives a TTL level to convert, it changes a TTL Logic 0 to between +3 and +15 V, and changes TTL Logic 1 to between -3 to -15 V, and vice versa for converting from RS232 to TTL. This can be confusing when you realize that the RS232 Data Transmission voltages at a certain logic state are opposite from the RS232 Control Line voltages at the same logic state. 

RS232 Level shifting

RS232 Protocol 

In telecommunications, RS-232 (Recommended Standard 232) is the traditional name for a series of standards for serial binary single-ended data and control signals connecting between a DTE (Data Terminal Equipment) and a DCE (Data Circuit-terminating Equipment). It is commonly used in computer serial ports. The standard defines the electrical characteristics and timing of signals, the meaning of signals, and the physical size and pinout of connectors. The current version of the standard is TIA-232-F Interface Between Data Terminal Equipment and Data Circuit-Terminating Equipment Employing Serial Binary Data Interchange, issued in 1997.

In RS-232, user data is sent as a time-series of bits. Both synchronous and asynchronous transmissions are supported by the standard. In addition to the data circuits, the standard defines a number of control circuits used to manage the connection between the DTE and DCE. Each data or control circuit only operates in one direction, that is, signaling from a DTE to the attached DCE or the reverse. Since transmit data and receive data are separate circuits, the interface can operate in a full duplex manner, supporting concurrent data flow in both directions. The standard does not define character framing within the data stream, or character encoding. The RS-232 standard defines the voltage levels that correspond to logical one and logical zero levels for the data transmission and the control signal lines. Valid signals are plus or minus 3 to 15 volts; the ±3 V range near zero volts is not a valid RS-232 level. The standard specifies a maximum open-circuit voltage of 25 volts: signal levels of ±5 V, ±10 V, ±12 V, and ±15 V are all commonly seen depending on the power supplies available within a device. RS-232 drivers and receivers must be able to withstand indefinite short circuit to ground or to any voltage level up to ±25 volts. 

The slew rate, or how fast the signal changes between levels, is also controlled. For data transmission lines (TxD, RxD and their secondary channel equivalents) logic one is defined as a negative voltage, the signal condition is called marking, and has the functional significance. Logic zero is positive and the signal condition is termed spacing. Control signals are logically inverted with respect to what one sees on the data transmission lines. When one of these signals is active, the voltage on the line will be between +3 to +15 volts. The inactive state for these signals is the opposite voltage condition, between −3 and −15 volts. Because both ends of the RS-232 circuit depend on the ground pin being zero volts, problems will occur when connecting machinery and computers where the voltage between the ground pin on one end, and the ground pin on the other is not zero. This may also cause a hazardous ground loop. Use of a common ground limits RS-232 to applications with relatively short cables. If the two devices are far enough apart or on separate power systems, the local ground connections at either end of the cable will have differing voltages; this difference will reduce the noise margin of the signals. Unused interface signals terminated to ground will have an undefined logic state. Where it is necessary to permanently set a control signal to a defined state, it must be connected to a voltage source that asserts the logic 1 or logic 0 level. Some devices provide test voltages on their interface connectors for this purpose.

HT12D DECODER for Engineering projects

HT12D DECODER  for Engineering projects

The 212 decoders are a series of CMOS LSIs for remote control system applications. They are paired with Holtek 212 series of encoders (refer to the encoder/decoder cross reference table). For proper operation, a pair of encoder/decoder with the same number of addresses and data format should be chosen.

The decoders receive serial addresses and data from a programmed 212 series of encoders that are transmitted by a carrier using an RF or an IR transmission medium. They compare the serial input data three times continuously with their local addresses. If no error or unmatched codes are found, the input data codes are decoded and then transferred to the output pins. 

The VT pin also goes high to indicate a valid transmission. The 212 series of decoders are capable of decoding information that consists of N bits of address and 12_N bits of data. Of this series, the HT12D is arranged to provide 8 address bits and 4 data bits. Operation The 212 series of decoders provides various combinations of addresses and data pins in different packages so as to pair with the 212 series of encoders. The decoders receive data that are transmitted by an encoder and interpret the first N bits of code period as addresses and the last 12_N bits as data, where N is the address code number.

The oscillator is disabled in the standby state and activated when a logic high signal applies to the DIN pin. That is to say, the DIN should be kept low if there is no signal input. The received data and address is checked thrice before setting the VT high.

HT12E Encoder for Engineering projects

HT12E Encoder for Engineering projects

  Most of the Engineering projects need the HT12E encoder for remote controlled systems applications.

They are capable of encoding information which consists of N address bits and 12_N data bits. Each address/ data input can be set to one of the two logic states. The programmed addresses/data are transmitted together with the header bits via an RF or an infrared transmission medium upon receipt of a trigger signal. The capability to select a TE trigger on the HT12E or a DATA trigger on the HT12A further enhances the application flexibility of the 212 series of encoders.

Operation The 212 series of encoders begin a 4-word transmission cycle upon receipt of a transmission enable (TE for the HT12E or D8~D11 for the HT12A, active low). This cycle will repeat itself as long as the transmission enable (TE or D8~D11) is held low. Once the transmission enable returns high the encoder output completes its final cycle and then stops as shown in the timing diagram shown above. 

The status of each address/data pin can be individually pre-set to logic _high_ or _low_. If a transmission- enable signal is applied, the encoder scans and transmits the status of the 12 bits of address/ data serially in the order A0 to AD11 for the HT12E encoder and A0 to D11 for the HT12A encoder. During information transmission these bits are transmitted with a preceding synchronization bit. If the trigger signal is not applied, the chip enters the standby mode and consumes a reduced current of less than 1_A for a supply voltage of 5V. Usual applications preset the address pins with individual security codes using DIP switches or PCB wiring, while the data is selected by push buttons or electronic switches. For the HT12E encoders, transmission is enabled by applying a low signal to the TE pin. 

The address pins of the encoder are joined with controller’s port 0. The data pins of the encoder are linked with controllers port P2.0 to P2.3.Once the data and address are set by the controller, the transmission enable pin of the encoder connected with the pin P2.4 of the controller is set to LOW. Thus enabling the transmission, the data is sent to the RF transmitter module , transmitting the signal continuously till the transmission enable pin to set to HIGH.

History and Scope of RFID

History and Scope of RFID

Radio-frequency identification (RFID) is a technology that uses communication through the use of radio waves to exchange data between a reader and an electronic tag attached to an object, for the purpose of identification and tracking.

HISTORY:

In 1945 Leon Theremin invented an espionage tool for the Soviet Union which retransmitted incident radio waves with audio information. Sound waves vibrated a diaphragm which slightly altered the shape of the resonator, which modulated the reflected radio frequency. Even though this device was a covert listening device, not an identification tag, it is considered to be a predecessor of RFID technology, because it was likewise passive, being energized and activated by waves from an outside source.

Similar technology, such as the IFFtransponder developed in the United Kingdom, was routinely used by the allies in World War II to identify aircraft as friend or foe. Transponders are still used by most powered aircraft to this day. Another early work exploring RFID is the landmark 1948 paper by Harry Stockman, titled "Communication by Means of Reflected Power" . Stockman predicted that "... considerable research and development work has to be done before the remaining basic problems in reflected-power communication are solved, and before the field of useful applications is explored."

Mario Cardullo's device in 1973 was the first true ancestor of modern RFID, as it was a passive radio transponder with memory. The initial device was passive, powered by the interrogating signal, and was demonstrated in 1971 to the New York Port Authority and other potential users and consisted of a transponder with 16 bit memory for use as a toll device. The basic Cardullo patent covers the use of RF, sound and light as transmission media. The original business plan presented to investors in 1969 showed uses in transportation (automotive vehicle identification, automatic toll system, electronic license plate, electronic manifest, vehicle routing, vehicle performance monitoring), banking (electronic check book, electronic credit card), security (personnel identification, automatic gates, surveillance) and medical (identification, patient history).

An early demonstration of reflected power (modulated backscatter) RFID tags, both passive and semi-passive, was performed by Steven Depp, Alfred Koelle, and Robert Freyman at the Los Alamos National Laboratory in 1973.The portable system operated at 915 MHz and used 12-bit tags. This technique is used by the majority of today's UHFID and microwave RFID tags.

The first patent to be associated with the abbreviation RFID was granted to Charles Walton in 1983.

The largest deployment of active RFID is the US Department of Defense use of Savi active tags on every one of its more than a million shipping containers that travel outside of the continental United States. The largest passive RFID deployment is the enterprise-wide deployment performed by Wal*Mart which instrumented over 2800 retail stores with over 25,000 reader systems, however the exact number is considered 'corporate confidential'.

2.1.1 DEVELOPMENT:

RFIDs are easy to conceal or incorporate in other items. For example, in 2009 researchers at Bristol University successfully glued RFID micro-transponders to live ants in order to study their behaviour. This trend towards increasingly miniaturized RFIDs is likely to continue as technology advances.

Hitachi holds the record for the smallest RFID chip, at 0.05mm x 0.05mm. This is 1/64th the size of the previous record holder, the mu-chip. Manufacture is enabled by using the silicon-on-insulator (SOI) process. These dust-sized chips can store 38-digit numbers using 128-bit Read Only Memory (ROM). A major challenge is the attachment of the antennas, thus limiting read range to only millimetres.

Potential alternatives to the radio frequencies (0.125–0.1342, 0.140–0.1485, 13.56, and 840–960 MHz) used are seen in optical RFID (or OPID) at 333 THz (900 nm), 380 THz (788 nm), 750 THz (400 nm). The awkward antennas of RFID can be replaced with photovoltaic components and IR-LEDs on the ICs.

 SCOPE OF RFID:

RFID has many applications; for example, it is used in enterprise supply chain management to improve the efficiency of inventory tracking and management. The Healthcare industry has used RFID to create tremendous productivity increases by eliminating "parasitic" roles that don't add value to an organization such as counting, looking for things, or auditing items. Many financial institutions use RFID to track key assets and automate Sarbanes Oxley SOX compliance. Also with recent advances in social media RFID is being used to tie the physical world with the virtual world. RFID in Social Media first came to light in 2010 with facebook's annual conference.

Barcode systems though used for product information, inventory control, etc have some drawbacks as compared to RFID. The amount of information stored in a barcode is very less as compared to RFID. RFID can store up to 1000 bytes of data. An RFID is specific to each item, whereas the barcode is not. Barcode needs human interaction for proper operation. It requires time-of-sight access to an optical scanner for the product related information. The barcode is to be replaced if the information it contains needs modification, but in RFID it can be modified at stages of the supply chain by the interaction between the microchip and the reader software. The barcode system is less accurate as compared to RFID.
 Working of  RFID click here

Global Positioning System - Working

Global Positioning System - Working
GPS system says the location of any object on earth. We hear about GPS mobile phones, but what is a GPS? and How it is functioning? I would like to share the basics and working of a GPS here.

GPS Working (Picture from: Google images)

INTRODUCTION

The Global Positioning System (GPS) is a satellite-based navigation system made up of a network of 24 satellites placed into orbit by the U.S. Department of Defense. GPS provides specially coded satellite signals that can be processed in a GPS receiver, enabling the receiver to compute position, velocity and time. GPS essentially consists of three segments namely Space segment, Control Segment and User Segment.

SPACE SEGMENT

The Space Segment of the system consists of the GPS satellites. These Space Vehicles (SVs) send radio signals from space. The nominal GPS Operational Constellation consists of 24 satellites that orbit the earth in 12 hours. There are often more than 24 operational satellites as new ones are launched to replace older satellites. The satellite orbits repeat almost the same ground track (as the earth turns beneath them) once each day. The orbit altitude is such that the satellites repeat the same track and configuration over any point approximately each 24 hours (4 minutes earlier each day). There are six orbital planes (with nominally four SVs in each), equally spaced (60 degrees apart), and inclined at about fifty-five degrees with respect to the equatorial plane. This constellation provides the user with between five and eight SVs visible from any point on the earth.

CONTROL SEGMENT

The Control Segment consists of a system of tracking stations located around the world. The Master Control facility is located at Schriever Air Force Base (formerly Falcon AFB) in Colorado. These monitor stations measure signals from the SVs which are incorporated into orbital models for each satellites. The models compute precise orbital data (ephemeris) and SV clock corrections for each satellite. The Master Control station uploads ephemeris and clock data to the SVs. The SVs then send subsets of the orbital ephemeris data to GPS receivers over radio signals.

USER SEGMENT

The GPS User Segment consists of the GPS receivers and the user community. GPS receivers convert SV signals into position, velocity, and time estimates. Four satellites are required to compute the four dimensions of X, Y, Z (position) and Time. GPS receivers are used for navigation, positioning, time dissemination, and other research. Navigation in three dimensions is the primary function of GPS. Navigation receivers are made for aircraft, ships, ground vehicles, and for hand carrying by individuals

WORKING

GPS satellites circle the earth twice a day in a very precise orbit and transmit signal information to earth. GPS receivers take this information and use triangulation to calculate the user's exact location. Essentially, the GPS receiver compares the time a signal was transmitted by a satellite with the time it was received. The time difference tells the GPS receiver how far away the satellite is. Now, with distance measurements from a few more satellites, the receiver can determine the user's position and display it [2].

A GPS receiver must be locked on to the signal of at least three satellites to calculate a 2D position (latitude and longitude) and track movement. With four or more satellites in view, the receiver can determine the user's 3D position (latitude, longitude and altitude). Once the user's position has been determined, the GPS unit can calculate other information, such as speed, bearing, track, trip distance, distance to destination, sunrise and sunset time and more.

SIGNALS

The SVs transmit two microwave carrier signals. The L1 frequency (1575.42 MHz) carries the navigation message and the SPS code signals. The L2 frequency (1227.60 MHz) is used to measure the ionospheric delay by PPS equipped receivers. The signals travel by line of sight, meaning they will pass through clouds, glass and plastic but will not go through most solid objects such as buildings and mountains.

A GPS signal contains three different bits of information — a pseudorandom code, ephemeris data and almanac data. The pseudorandom code is simply an I.D. code that identifies which satellite is transmitting information. Ephemeris data tells the GPS receiver where each GPS satellite should be at any time throughout the day. Each satellite transmits ephemeris data showing the orbital information for that satellite and for every other satellite in the system. Almanac data, which is constantly transmitted by each satellite, contains important information about the status of the satellite (healthy or unhealthy), current date and time. This part of the signal is essential for determining a position.