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Sunday 20 February 2011

Proximity Detectors Block Diagram Using TDA161

This is a circuit that illustrated the Proximity Detectors Block Diagram using TDA161 from ST Semiconductor. The TDA161 is a monolithic integrated circuits produced and designed by ST semiconductor to be used for metallic body detection by sensing variations in high frequency Eddy current losses. This is the figure of the circuit;


Proximity Alarm Circuit

This is a design circuit for proximity circuit that can be used in alarm circuit. This is the figure of the circuit;


Inverters U1a and U1b are connected in a simple RC oscillator circuit. The frequency is determined by the values of R1, C1 C2 and the internal characteristics of the integrated circuit. As long as the circuit is oscillating, a positive dc voltage is developed at the output of the voltage-couple circuit: C3, D2 and C4. The dc voltage is applied to the input of U1c-the third inverter amplifier-keeping its output in a low state, which keeps Q1 turned off so that no sound is produced by BZ1. With C1 and C2 adjusted to the most sensitive point, the pickup plate will detect a hand 3 to 5-inches away and sound an alert. Set C1 and C2 to approximately one-half of their maximum value and apply power to the circuit. The circuit should oscillate and no sound should be heard. Using a non-metallic screwdriver, carefully adjust C1 and C2, one at a time, to a lower value until the circuit just ceases oscillation: Buzzer BZ1 should sound off. Back off either C1 or C2 just a smidgen until the oscillator starts up again-that is the most sensitive setting of the circuit.

Ambient Light Ignoring Active Motion Detector Circuit

This is a design circuit for motion detector uses the same basic concept as the active infrared motion detector. An interruption in a 5 kHz modulated pulsating beam that is transmitted by an infrared diode and received by an infrared transistor sets off the alarm. This is the figure of the circuit;


The circuit on the left is the transmitter circuit that establishes a 5 kHz modulated infrared beam. As you can see from the schematic of the receiver circuit, a resonance-tuned narrowband amplifier reduces the detector`s sensitivity to stray light. C1 and L1 in IC2A`s feedback loop cause the op amp to pass only those frequencies at or near the LED`s 5 kHz modulation rate. IC2B`s output increases when the received signal is sufficient to drop the negative voltage across C2 below the reference set by R2. The output of this circuit is then attached to some load resistance, which can be an alarm or, for demonstration purposes, an LED.

Active IR Motion Detector Circuit

Here’s the circuit that can be used to detect motion in an area where there are not supposed to be any moving objects using ultrasonic motion detector. This type of motion detector is most commonly used in burglar alarm systems since they are very effective in this application. This is the figure of the circuit;


There are tw1o transducers: one emits an ultrasonic wave and the other picks up reflections from the different objects in the area. The reflected waves arrive at the receiver in constant phase if none of the objects in the area are moving. If something moves, the received signal is shifted in phase. A phase comparator detects the shifted phase and sends a triggering pulse to the alarm.

Thursday 10 February 2011

Magnetic Proximity Switch Circuit

This is a design circuit of a magnetic proximity switch that finds a lot of applications in many fields. The circuit is based on a magnetic reed switch(S1) as the proximity sensor. A mono stable multi vibrator based on NE555 (IC1) and a toggle flip flop based on CD4013 (IC2) does the rest of the circuit. This is the figure of the circuit;
 
 
When a magnet is reached in proximity of S1 it closes to give a negative trigger at pin 2 of IC1.The output of IC1 goes high for a time determines by R2 and C2.This clocks the IC2 wired as a toggle flip flop. The output (pin 1) of IC2 goes high and the transistor Q1 is biased to ON. The relay is activated and so do the equipment connected to the relay. The LED D1 glows when IC1 is triggered. The equipment to control can be connected using NC, NO and C points of the relay according to the application. Switch S1 can be a general purpose magnetic reed switch. Use a 12 regulated power supply for powering the circuit.

Solar Relay Circuit

Here’s a design circuit for solar relay. This is a simple design circuit. This is the figure of the circuit;


This is the operating principle of the solar relay. The trick to this apparently rather simple circuit consists of using a suitable combination of components. Instead of a power FET, it employs a special 12-V relay that can handle a large load in spite of its small size. This relay must have a coil resistance of at least 600 Ω, rather than the usual value of 100-200 Ω. This requirement can be met by several Schrack Components relays (available from, among others, Conrad Electronics). Here we have used the least expensive model, a type RYII 8-A printed circuit board relay. The light probe is connected in series with the relay. It consists of two BPW40 photo transistors wired in parallel. he type number refers to the 40-degree acceptance angle for incident light. In bright sunlight, the combined current generated by the two photo transistors is sufficient to cause the relay to engage, in this case without twitching. Every relay has a large hysteresis, so the fan connected via the a/b contacts will run for many minutes, or even until the probe no longer receives sufficient light. The NTC thermistor connected in series performs two functions. First, it compensates for changes in the resistance of the copper wire in the coil, which increases by approximately 4 percent for every 10 ºC increase in temperature, and second, it causes the relay to drop out earlier than it otherwise would (the relay only drops out at a coil voltage of 4 V).

Analog Signal From Proximity Circuit

Connecting the output of the ir proximity circuit to the analog input to the Arduino board to create an analog value. In this example, that value controls the rate at which an LED blinks. We connect three wires to the Arduino board. The first goes to ground from ir proximity circuit. The second goes from 5 volts of the circuit. The third goes from the output pin of the circuit to analog input 2 on the Arduino board. Here the figure of the design circuit;
 

By placing your open palm in front of the ir proximity circuit, we change the amount current that is output by the ir proximity circuit. This changes the relative "closeness" of that pin to 5 volts and ground, giving us a different analog input. When the hand is moved away from the ir circuit less volts will be output to the pin. When the hand is moved close to the ir circuit more volts are output to the pin. AnalogRead() returns a number between 0 and 1023 that is proportional to the amount of voltage being applied to the pin. There are significant amounts of the infrared spectrum is contained within ambient light. Therefore the infrared signal detected by the proximity sensor can be noisy and contain light other than from the original source. To improve the accuracy of the ir sensor the transmitted infrared light should be modulated using a timer such as the 555 timer chip. The NAND gate is a standard 74LS00 that you can get anywhere - even Radio Shack, same with the 555, IR detector (RS Everlight or Sharp GP1U58Y) and IR LEDs can also be gotten at Radio Shack. Parts are easy to find and simple to connect. This does not require any fancy wiring or parts placement. Make sure that you use a .1uf bypass cap next to the 555 and next to the IR demodulator. Tweak the 2K pot until you have 38KHz, if you have a 'scope, this is a 1/38,000 period, or about 26.3us. With Arduino you can feed the output of the 555 in an I/O port and measure the frequency very easily.

Sunday 6 February 2011

Pressure Transducer Bridge Monitor Circuit Using AD620

This is a circuit for a 3kOhms pressure transducer bridge that operates on a 5V single supply is shown in the figure below. This is the figure of the circuit;


In the circuit like this, bridge consumes only 1,7mA. The using of AD620 and a buffered voltage divider allows the signal to be conditioned for only 3.8mA of total supply current. Where small size and low power become more significant, the AD620 is suitable for higher resistance and pressure sensors powered at lower voltages.

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