PIR Circuits

Motion Sensor Light

Turns on a White LED for 3 minutes and turns off when a human move in front of it. Uses Passive Infra Red (PIR) motion sensor.

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Op Amp Circuits

Op Amp Schmitt trigger

The Op Amp comparators sometimes works well under some conditions but not always. If there is a slow wave form or some noise on it, sometimes the output switch back and forth many times. So for stable operation, Op Amp comparator can be designed as a Schmitt trigger.
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LED circuits

Power status LED

Two LEDs indicate the power on and off status of bread board power . So it helps to confirm whether the positive and negative rails of the bread board are getting power. Green LED lights at power on and turns off after 3 seconds. Red LED turns on at power off and turns off after 3 seconds. Let us see the circuit

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AC Circuits


It is easy to light an LED by directly connected to 220 volt AC. It can be indicator in AC devices or Bed lamp if White LED is used. If used as a Bed lamp, the circuit can be enclosed in a plug  with LED projecting out.

Caution : The circuit is directly connected to high voltage that can give a fatal shock if handled carelessly . Do not test or troubleshoot when connected to mains. 

AC Circuits

Simple Power Failure Alarm

Beep once when power fails. 12 volt relay is used as a switch. When power is available, relay pulls and capacitor charges via diode D1 and NO and Common contacts of relay. When power fails, relay turns off and capacitor discharges via Common and NC contacts and buzzer. Buzzer gives a short beep at that time. If more timing for beep is needed, connect one more 4700 capacitor parallel to C1. 12 Volt DC for the circuit should be from a 12 Volt adapter or transformer power supply.