Precision Full Wave Ac Dc Converter Circuit Diagram

A dc level is produced that corresponds to the ac input rms value (if sine wave), -i set the gain of IC2 to 1.11. This factor is the average-to-rms conversion factor. IC1 and IC2 act as a full-wave rectifier circuit, with Dl and D2. 

Precision Full-Wave Ac/Dc Converter Circuit Diagram

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Long Range Cordless Burglar Alarm

This long-range cordless burglar alarm circuit makes use of a cordless telephone (CLT) unit with paging facility and a few low-cost discrete components. The circuit is so simple that even a novice can easily construct it without any difficulty. When the ‘page’ button on a CLT is pressed and held in that position, the handset starts beeping to indicate that somebody is calling. This function is used here to build the gadget. The system consists of three sub-assemblies:

   

1. Wireless beeper. The handset of the CLT.

2. Infrared transmitter. A number of IR transmitter circuits based on the well-known 555 chip have been published earlier in EFY. Just select one circuit with a modulating frequency of 36 to 38 kHz and assemble it on a veroboard. After that, enclose it in a proper cabinet. (EFY note. A typical IR transmitter circuit used during testing is shown in Fig. 1.)

 

3. Infrared receiver-cum-control unit. The circuit diagram of this unit is shown in Fig. 2. Front end of this block is Sharp’s GP1U561X integrated infrared re-ceiver module (or TK1836/ TSOP1836 from Temic/ Telefunken, etc). This mod-ule can demodulate 36kHz modulated IR beam to pro-duce an active-similar  ‘low’ output. You may also use any other module, provided it has an active-‘low’ output. The modulated IR beam from the transmitter is received by the receiver module and its output at pin 2 goes ‘low’. The rest of the circuit is in sleep mode as it does not get power for its operation. The SCR here plays the role of an electronic switch.

When the infrared beam is interrupted, the output of the receiver module goes ‘high’ to apply a forward bias to the base of transistor T1. As a result, the gate of SCR gets sufficient forward bias to conduct (and latch). The astable multivibrator built around IC1 starts working to control the  ‘on’/‘off’ relay timings. Diode D1 prevents the relay from latching and diode D2 works as a free-wheeling diode.

Normally open (N/O) contacts of the relay are used to close the  ‘page’ button contacts until the circuit is reset by pressing push-to-off switch S1 (N/C type). One may replace switch S1 with a key-lock switch to avoid its unauthorised operation. The astable circuit helps the hand-set user to distinguish between a normal paging call and an intrusion warning alarm.

After construction, fix the transmitter and receiver modules at opposite sides in the door frame as shown in Fig. 3. Carefully open the CLT and solder two wires to the  ‘page’ button terminals with their free ends connected to the relay contacts (N/O). Now your cordless burglar alarm with a wireless monitoring range of about 500 meters (actual range is based on the CLT’s paging range) is ready to detect an intruder.

EFY note. The author has success-fully tested his prototype with the following CLT makes:

• Panasonic KX-T 3611 BH (made in Japan)
• Panaphone WT-3990 (made in China)
• Citizen JRT-5400 (made in India)

Source:   http://www.ecircuitslab.com/2012/01/long-range-cordless-burglar-alarm.html

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Clever Rain Alarm

Usually rain-alarms employ a single sensor. A serious draw-back of this type of sensor is that even if a single drop of water falls on the sensor, the alarm would sound. There is a probability that the alarm may be false. To overcome this draw-back, here we make use of four sensors, each placed well away from the other at suitable spots on the roof. The rain alarm would sound only if all the four sensors get wet. This reduces the probability of false alarm to a very great extent. The four rain-sensors SR1 to SR4, along with pull-up resistors R1 to R4 (connected to positive rails) and inverters N1 to N4, form the rain-sensor monitor stage. The sensor wires are brought to the PCB input points E1 to E5 using a 5-core cable. The four outputs of Schmitt inverter gates N1 to N4 go to the four inputs of Schmitt NAND gate N7, that makes the alarm driver stage.

Clever Rain-Alarm Circuit Diagram

When all four sensors sense the rain, all four inputs to gates N1 through N4 go low and their outputs go high. Thus all four in-puts to NAND gate N7 also go high and its output at pin 6 goes to logic 0. The out-put of gate N7 is high if any one or more of the rain-sensor plates SR1 through SR4 remain dry. The output of gate N7 is coupled to inverter gates N5 and N6. The output from gate N5 (logic 1 when rain is sensed) is brought to  ‘EXT’ output connector, which may be used to control other external devices.

The output from the other inverter gate N6 is used as enable input for NAND gate N8, which is configured as a low-frequency oscillator to drive/modulate the piezo buzzer via transistor T1. The frequency of the oscillator/modulator stage is variable between 10 Hz and 200 Hz with the help of preset VR1. The buzzer is of piezo-electric type having a continuous tone that is inter-rupted by the low-frequency output of N8. The buzzer will sound whenever rain is sensed (by all four sensors). 6V power supply (100mA) is used here to enable proper interfacing of the CMOS and TTL ICs used in the circuit. The power supply requirement is quite low and a 6-volt battery pack can be easily used. During quiscent-state, only a negligible cur-rent is consumed by the circuit.

Even during active state, not more than 20mA current is needed for driving a good-quality piezo-buzzer. Please note that IC2, being of TTL type, needs a 5V regulated supply. There-fore zener D1, along with capacitor C2 and resistor R5, are used for this purpose.A parallel-track, general-purpose PCB or a veroboard is enough to hold all the components. The rain-sensors SR1 to SR4 can be fabricated as shown in the construction guide in Fig. 2. They can be made simply by connecting alternate parallel tracks using jumpers on the component side.

Use some epoxy cement on and around the wire joints at A and B to avoid corrosion. Also, the sensors can be cemented in place with epoxy cement. If the number of sensors is to be increased, just add another set of CD40106 and 7413 ICs along with the associated discrete components. Another good utility of the rain-alarm is in agriculture. When drip-irrigation is employed, fix the four sensors at four corners of the tree-pits, at a suit-able height from the ground. Then, as soon as the water rises to the sensor’s level, the circuit can be used to switch off the water pump.

Author : M.K. Chandra Mouleeswaran - Copyright: EFY

Source: http://www.ecircuitslab.com/2011/12/clever-rain-alarm.html

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