Secret Diagram

Wednesday, 22 March 2017

Touch Switch II Circuit Diagram

This circuit uses a 555 timer as the bases of the touch switch. You can learn more about 555 timers in the Learning section on my site. When the plate is touched the 555 timer is triggered and the output on pin 3 goes high turning on the LED and the buzzer for a certain period of time. The time that the LED and the buzzer is on is based on the values of the capacitor and resistor connected to pin 6 & 7. The 10M resistor on pin 2 causes the the circuit to be very sensitive to the touch.

Touch Switch II Circuit Diagram

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Adjustable switching power supply

This circuit supplying current maximum10A with an adjustable output voltage from 0-25 VDC. Adjustable Switching Regulator L4970 Series is built with the main component as a Switching Regulator IC L4970.

Switching Regulator L4970 series include not complicated to make his own, which need to be considered is the IC L4970 require sufficient cooling to operate in an optimal and durable. Adjustable Switching Regulator L4970 series are complete can be seen in thethe following figure .

Adjustable switching power supply schematics

To set the output voltage range Adjustable Switching Regulator L4970 can be in control by adjusting the potentiometer 18KOhm tus.

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Car Anti Theft Wireless Alarm

This FM radio-controlled anti-theft alarm can be used with any vehicle having 6- to 12-volt DC supply system. The mini VHF, FM transmitter is fitted in the vehicle at night when it is parked in the car porch or car park. The receiver unit with CXA1019, a single IC-based FM radio module, which is freely available in the market at reasonable rate, is kept inside.

Receiver is tuned to the transmitter's frequency. When the transmitter is on and the signals are being received by FM radio receiver, no hissing noise is available at the output of receiver. Thus transistor T2 (BC548) does not conduct. This results in the relay driver transistor T3 getting its forward base bias via 10k resistor R5 and the relay gets energised.

Car Anti-Theft Wireless Alarm Circuit

When an intruder tries to drive the car and takes it a few metres away from the car porch, the radio link between the car (transmitter) and alarm (receiver) is broken. As a result FM radio module gene-rates hissing noise. Hissing AC signals are coupled to relay switching circuit via audio transformer. These AC signals are rectified and filtered by diode D1 and capacitor C8, and the resulting positive DC voltage provides a forward bias to transistor T2.

Thus transistor T2 conducts, and it pulls the base of relay driver transistor T3 to ground level. The relay thus gets de-activated and the alarm connected via N/C contacts of relay is switched on. If, by chance, the intruder finds out about the wireless alarm and disconnects the transmitter from battery, still remote alarm remains activated because in the absence of signal, the receiver continues to produce hissing noise at its output. So the burglar alarm is fool-proof and highly reliable. (Ed: You may have some problem catching the thief, though, if he decides to run away with your vehicle_in spite of the alarm!)

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Tuesday, 21 March 2017

Loudspeaker Protector Monitors Current

This circuit uses a 0.1O 1W resistor connected in series with the output of a power amplifier. When the amplifier is delivering 100W into an 8O load, the resistor will be dissipating 1.25W. The resulting temperature rise is sensed by a thermistor which is thermally bonded to the resistor. The thermistor is connected in series with a resistor string which is monitored by the non-inverting (+) inputs of four comparators in an LM339 quad comparator. All of the comparator inverting inputs are connected to an adjustable threshold voltage provided by trimpot VR1. As the thermistor heats up, its resistance increases, raising the voltage along the resistor ladder.

Loudspeaker Protector Monitors Current Circuit diagram:

Loudspeaker Protector Circuit Diagram

When the voltage on the non-inverting input of each comparator exceeds the voltage at its inverting input, the output switches high and illuminates the relevant LED. NOR gate latches are connected to the outputs of the third and fourth comparators. When the third comparator switches high, the first latch is set, turning on Q1 and relay 1. This switches in an attenuation network (resistors RA & RB) to reduce the power level. However, if the power level is still excessive, comparator 4 will switch, setting its latch and turning on Q2 and relay 2.

This disconnects the loudspeaker load. The thermistor then needs to cool down before normal operation will be restored. The values of R1-R4 depend on the thermistor used. For example, if a thermistor with a resistance of 1.5kO at 25°C is used, then R1 could be around 1.5kO and R2, R3 and R4 would each be 100O (depending the temperature coefficient of the thermistor). The setup procedure involves connecting a sinewave oscillator to the input of the power amplifier and using a dummy load for the output. Set the power level desired and adjust trimpot VR1 to light LED1. Then increase the power to check that the other LEDs light at satisfactory levels.

Author: David Devers - Copyright: Silicon Chip Electronics

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Monday, 20 March 2017

SLD of roof top solar system

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AC Mains Bistable Switch

AC Mains Bistable Switch Circuit Diagram. This AC mains-operated bistable switch turns on or turns off a device using a miniature neon lamp and a few discrete components. This switch can be used for control pan-els, appliances and lighting controls. A push-to-on switch is used to light up the neon lamp. The light emit-ted by the neon lamp, in turn, enables the switching action of the circuit. Use of a 555 timer wired for bistable operation makes the circuit act as a bistable switch.
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Circuit diagram :

AC Mains Bistable Switch Circuit Diagram

The neon lamp (NL1) and the push-to-on switch (S1) are directly connected to 230V AC mains. The 12V DC supply for timer 555 (IC1) is derived from 230V AC mains through capacitive dropper C1, resistor R1 and a 12V zener diode. IC1 works as a flip-flop circuit, with the signal at its output pin 3 toggling every time it receives a pulse at its pins 2 and 6.

The operation of the circuit is simple. When you press switch S1 momentarily, the neon lamp glows, making phototransistor T1 conduct to provide a pulse at pins 2 and 6 of IC1. When switch S1 is pressed, the output of IC1 goes high and LED1 glows. Pressing S1 again makes the output of IC1 low and LED1 stops glowing.

In place of LED1, you can use an optodiac or suitable relay (not shown in the circuit) along with a suitable driver circuit to drive AC loads. Assemble the circuit on a general-purpose PCB with the neon lamp and the phototransistor housed in a small black tube isolated from the external light source, and enclose in a suitable cabinet. Fix switch S1 on the front panel of the cabinet, and mains power cord at the rear. At the rear, also fix a 3-pin socket to connect the AC load.

Caution. Take care when operating this circuit as it is directly connected to 230V AC mains. Better still, don’t attempt this circuit if you have no experience in handling high-voltage circuits.

Author : T.A. Babu- Copyright : EFY

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Sunday, 19 March 2017

LDO Regulator

Recently the author had to adapt a standard circuit configuration (which often uses an npn bipolar) so as to operate as a low-dropout (LDO) regulator. The circuit shown here uses that rarity, a depletion-mode MOSFET to implement the LDO function. What to do when you have to derive an analogue supply voltage (close to +5 V) from an existing ‘digital’ 5-volt rail, ensuring sufficient decoupling between the two? One answer is to step up and then use a linear regulator to step back down. However, if around 4.5 volts will suffice then an alternative is a home-made LDO regulator. The circuit is usually a fairly standard shape typically a npn transistor (with base-current limiting resistor) is used.

Circuit diagram :

LDO-Regulator-Circuit Diagram

LDO Regulator Circuit Diagram

Initially, it would appear that this design suffices after all, the text books say the saturation voltage is around 0.2 V. Unfortunately, this is no longer true when the collector is tied directly to the positive supply. An enhancement-mode MOSFET suffers similar disadvantages: with the drain tied High you need greater than drain potential at the gate to achieve low RDS(on). Enter that seldom-used beast the depletion-mode MOSFET! Depletion-mode MOSFETS are ‘on’ even when V gs = 0, and you have to back-bias the gate to achieve an increase in channel resistance.In the circuit shown the BSS139, an NMOS depletion device, operates with the gate forward biased. With a load of 10 mA, the measured FET resistance was 38 ohms.

Author :Stephen Bernhoeft - Copyright : Elektor electronics

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