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Fitting switches which turn off automatically after a preset time in these locations can reduce the electricity consumed quite significantly. A single 100W bulb left burning all night (say eight hours) would consume 800W/hrs. The same bulb fitted with a switch which turned off automatically after say five minutes would consume only 83W/hrs, even in the unlikely event that it were to be activated ten times during this period. Triac Control There are two major problems to solve when designing a touch switch to replace a conventional mechanical light switch and these concern the power supply and noise immunity. The main switching element used to control the light is a triac, a semiconductor a.c. switch. This is normally in its off or non-conducting state but can be switched into conduction by means of a small trigger current fed to its gate terminal. Once triggered it will remain conducting until the current through it drops below a certain value (known as the holding current). This occur...

This circuit uses a NE555 timer and CD4020B. When +12 Vdc is applied to the circuit, the output of IC2 is set low via C2, which turns on the relay, and IC1, a pulse generator. Auto Turn-Off Alarm With 8-Minute Delay Circuit Schematic IC1 pulses counter IC2. After 8192 clocks, IC2 output (pin 3) goes high, cuts off Q2, and completes the cycle.

This is a Simple Auto Turn-Off Alarm With 8-Minute Delay Circuit Project. This circuit uses a NE555 timer and CD4020B. When +12 Vdc is applied to the circuit, the output of IC2 is set low via C2, which turns on the relay, and IC1, a pulse generator. IC1 pulses counter IC2. After 8192 clocks, IC2 output (pin 3) goes high, cuts off Q2, and completes the cycle. Simple Auto Turn-Off Alarm With 8-Minute Delay Circuit Diagram

The power line fluctuations and cut-offs cause damages to electrical appliances connected to the line. It is more serious in the case of domestic appliances like fridge and air conditioners. If a fridge is operated on low voltage, excessive current flows through the motor, which heats up, and get damaged. The under/over voltage protection circuit with time delay presented here is a low cost and reliable circuit for protecting such equipments from damages. Whenever the power line is switched on it gets connected to the appliance only after a delay of a fixed time. If there is hi/low fluctuations beyond sets limits the appliance get disconnected. The system tries to connect the power back after the specific time delay, the delay being counted from the time of disconnection. If the power down time (time for which the voltage is beyond limits) is less than the delay time, the power resumes after the delay: If it is equal or more, then the power resumes directly. This circuit has been desig...

The M65831A is an IC developed for producing echo effects added to voice signals picked up by microphone for karaoke applications. The IC has the largest memory among the digital delay series. As it’s design is aimed at high performance, it is best suited to provide radio cassette tape recorders and miniature unit audio system with quality echo function. Being pin compatible with the M65830CP / FP and M65843AP / FP, the M65831AP / FP is suitable for upgrading the series. Circuit diagram: DIGITAL ECHO DIGITAL DELAY Datasheet for M65831A: Download