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.