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Tuesday, October 4, 2011

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.

Monday, September 26, 2011

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.

Sunday, September 25, 2011

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.

Wednesday, September 21, 2011


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.

Friday, September 16, 2011

IC ULN 2803 driver circuit

IC ULN 2803 driver circuit
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 

Wednesday, September 14, 2011

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.

Tuesday, September 13, 2011

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. 
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

Monday, September 12, 2011

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.

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.

Sunday, September 11, 2011

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 Receiver

Wednesday, September 7, 2011

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 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.

Tuesday, September 6, 2011

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.

Monday, September 5, 2011

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.

Wednesday, August 3, 2011

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.
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'.

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.

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

Sunday, July 24, 2011

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)
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.
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.
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.
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
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.
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.

Tuesday, June 28, 2011

Systems, Control Systems and Classifications

Systems, Control Systems and Classifications
System: A system comprises of several component work together for a specific task
Control System: If the output is of our desire and able to control, then the system is called as Control systems

General Classification of systems:
1.  Open loop System: In an Open loop System, the control action is independent of the desired output.

When  the output quantity of  the control system  is not  fed back  to  the  input quantity,  the control system is called an Open loop System. e.g. Blind man's action, traffic control without traffic police

2.  Closed loop System: In the Closed  loop Control System the control action is dependent on the desired output, where the output quantity is considerably controlled by sending a command signal to input quantity. The closed loop systems are normally have feed back.
e.g Normal man's action, Automobile systems, traffic signal control with traffic police etc.

Based on the type of system, control systems can be classified as
1.Electrical System,
2. Mechanical System (Translational, Rotational)
3. Hydraulic system
4. Pneumatic systems
5. Thermal systems and so on.

Wednesday, April 6, 2011


SECURITY ISSUES in SCADA based systems

The move from proprietary technologies to more standardized and open solutions together with the increased number of connections between SCADA systems and office networks and the Internet has made them more vulnerable to attacks - see references. Consequently, the security of SCADA-based systems has come into question as they are increasingly seen as extremely vulnerable to cyberwarfare/cyberterrorism attacks

SCADA systems are used to control and monitor physical processes, examples of which are electrical SCADA system would cause financial losses to all the customers that received electricity from that source. How security will affect legacy SCADA and new deployments remains to be seen. transmission of electricity, transportation of gas and oil in pipelines, water distribution, traffic lights, and other systems used as the basis of modern society. The security of these SCADA systems is important because compromise or destruction of these systems would impact multiple areas of society far removed from the original compromise. For example, a blackout caused by a compromised
There are two distinct threats to a modern SCADA system. First is the threat of unauthorized access to the control software, whether it be human access or changes induced intentionally or accidentally by virus infections and other software threats residing on the control host machine. Second is the threat of packet access to the network segments hosting SCADA devices. In many cases, there is rudimentary or no security on the actual packet control protocol, so anyone who can send packets to the SCADA device can control it. In many cases SCADA users assume that a VPN is sufficient protection and are unaware that physical access to SCADA-related network jacks and switches provides the ability to totally bypass all security on the control software and fully control those SCADA networks. These kinds of physical access attacks bypass firewall and VPN security and are best addressed by endpoint-to-endpoint authentication and authorization such as are commonly provided in the non-SCADA world by in-device SSL or other cryptographic techniques.
Many vendors of SCADA and control products have begun to address these risks in a basic sense by developing lines of specialized industrial firewall and VPN solutions for TCP/IP-based SCADA networks. Additionally, application white listing solutions are being implemented because of their ability to prevent malware and unauthorized application changes without the performance impacts of traditional antivirus scans Also, the ISA Security Compliance Institute (ISCI) is emerging to formalize SCADA security testing starting as soon as 2009. ISCI is conceptually similar to private testing and certification that has been performed by vendors since 2007. Eventually, standards being defined by ISA99 WG4 will supersede the initial industry consortia efforts, but probably not before 2011 .
The increased interest in SCADA vulnerabilities has resulted in vulnerability researchers discovering vulnerabilities in commercial SCADA software and more general offensive SCADA techniques presented to the general security community. In electric and gas utility SCADA systems, the vulnerability of the large installed base of wired and wireless serial communications links is addressed in some cases by applying bump-in-the-wire devices that employ authentication and Advanced Encryption Standard encryption rather than replacing all existing nodes.

Friday, January 28, 2011

Innovative revolutions in Credit card technologies

Technology updates on Credit cards
The credits cards are normally built with a magnetic strip which upon swiping at ATM or shopping centre will enable transactions. In the conventional cards, there is no facility of display card balance and keypads so on. There are many complaints from card holders of losing their money without their knowledge. This is mainly by the criminals who steal the data of the card using magnetic strip reader or noting down the card details, even cloning of the cards. To overcome these problems and completely preventing the theft or fraud, innovative revolution in the credit card technologies have emerged, some of the key technologies are addressed here.
Credit card with miniature display and keypads
The innovative technology has opened new windows for credit cards with display and keypad features. In these novel cards, the card is embedded with display and keypads so that the users can interact with them. This Credit card embedded authentication device can even provide additional security to prevent bank frauds for the users. These cards feature to display the current balance of the clients. Some card uses a one time pass code to authorize the online and phone transactions. These cards normally have built in batteries which will last for about 4 to 5 years. These programmable credit or master cards has yet to popularize the world for the cashless transactions.
Multi account and dynamic credit cards:
In this, we can store details of many cards and use any one card by choosing the magnetic strip of a particular card. This card also built in with a eInk display which consumes less power and no power if not displaying anything.
The dynamic cards are automatic reprogrammable magnetic strip where we can toggle between strips by using buttons and hide & show the desired credit card numbers with display facilities.
Credit card swipe phone or i-phone:
These phones are built with credit card reader facility where the entire transactions are done with phone. This is mainly useful for those doing micro finance and small business. The reader can be easily plugged into the audio jack. While swiping with this reader, the authentication is done with the mobile phone display.

The Braille Credit Card :
The Braille card specially designed to handle a visually challenged person to know the amount of money that has been charged on their card. The card with its Braille display features the Braille to know the sum that is needed to pay. The card also has an inbuilt miniature speaker which reads aloud the figures for further assistance. This special card can also be used by old aged people who suffer from poor eyesight with the features of built in speakers.

Thursday, January 27, 2011

Polygraph vs No Lie MRI scan as Lie detector

Polygraph vs No Lie MRI scan as Lie detector
Lie detectors are normally used for identifying criminals and employee screenings.
Polygraph has been used for a long time as lie detector and the emerging technology in this area is MRI scan technique which is very familiar in the medical arena.
Polygraph uses a couple of sensors for monitoring the pulse, sweating and breathing rate of the person to be tested. However the expert says that the polygraph results are error prone and struggle with its reliability. The main problem with this method is that the interpretation of a polygraph’s measurements is very tedious and chance of false identifying the truth tellers. According to an article from ieee spectrum, the false positive rate is a troublingly as high as 30 % and we can detect lies only between 64% to 100% of the time. The experts conclude that the polygraph testing probably works worse in the real world than in the lab.
The MRI scan technique is effectively used as lie detector by examining the brain activities. The prefrontal cortex part of the brain shows unusual activist upon detecting lies. In this process, Under a MRI Scan machine, the person is thrown a series of questions in front of his eyes and his brain is scanned through a special MRI scan. The scanning reports are analyzed.
Only few companies are opening up their store for this purpose worldwide. As MRI scan is so costly compared with polygraph technique, approximately 5000$ per test, it is not so popular among the people. Now a days the courts, law enforcement and business community are the clients of this technique.
Though many techniques may be on the road to test our truthfulness, my opinion is that it is better to be very honest and friendly with others rather than being untruthful person.

Friday, January 14, 2011

Internet based Scada System

Internet based Scada System

Supervisory Control and Data Acquisition (SCADA) systems are now becoming more and more popular in industrial processes and the demands in functionality and high performance have been increasing rapidly. Furthermore, the fast development of microprocessor and Micro controller manufacturing and Internet technology makes it more efficient and cost-saving to design such systems with the embedded network protocol modules.

The Internet has now been dedicating a new and highly-efficient medium for sharing information all over the world. The development of web technologies allows information to be displayed numerically and graphically on any conventional Internet browser. Via Internet browsers (or web-browsers), end users can access, monitor the real-time data and even control the field devices and equipments.

A solution on implementing Internet-based SCADA systems with the presence of embedded TCP/IP Protocol stacks can provide the following features:
• Automatically collect the latest system’s data and real-time data are displayed on web-browser interfaces.
• Users can manage and issue command controls on system’s devices from any internet-connected place.
• Security issue is carefully considered with: server protection by router; user authentication & IP approval on server application software and MD5 algorithm for data encoding. This helps reduce the threat of the public nature of the Internet.
• New sites/devices can be added/deleted/tracked.
• System operation can be tracked for each user by the event log tool.

Thursday, January 13, 2011

Telepresence robots

Telepresence robots
 Telepresence robot
    In the present world, we are all so busy in our business or daily works. Sometimes, it is too difficult to attend some of the important meetings, seminars or functions. In such places, our presence is inevitable to be part of the functions or meetings. So, the solution for such situations, The emerging Telepresence robot which can be easily controlled remotely through online with Wifi enabled controls.  This creates our presences in such occasions. You can show your presence anywhere with the help such amazing robo, where you can participate in the discussions, present, talk, or receiving anything from other side by merely having with your  laptop with net connectivity .

Thursday, January 6, 2011

Bubble Monorail system Shweeb - the winner of Google Innovation contest

Bubble Monorail system Shweeb - the winner of  Google Innovation contest

The bubble shaped monorail is designed with plastic pedaling facility for moving without using any of fuel. The bubble car is designed with 7 gears and run at a speed of 30 mph. This amazing rail has been tested in New Zealand’s firm of 218 long yard test track.
Another amazing with this car is that, it has won and received $1.05 million dollar Google’s Innovation contest.

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