Oct 032020
 

LED Pilot Light Circuit

This LED Pilot Light Circuit is intended to give us a visual warning that we have electronic equipment turned on. This is especially important on equipment that uses batteries.

That means that while the electronic equipment is working, the pilot light is ON showing that there is current consumption.

On many occasions, without realizing it, we leave ON a circuit or electronic equipment (that does not have a pilot light) and some time later we notice that the battery is completely discharged.

The proposed circuit can be connected in parallel to any existing 9 to 12V electronic circuit or equipment we want to monitor.
LED Pilot Light Circuit

LED Pilot Light Circuit – Power ON / OFF LED light

The current consumption of a LED could be very high for electronic equipment using small batteries, but the method used here avoids this problem.

LED Pilot Light Operation

A practical option to reduce the current consumption of the LED is to turn it on for very short periods of time. This oscillation will turn it on once every second, thus the battery charge will not be significantly reduced, even with small batteries.

Another advantage of a flashing light is that it is more noticeable than one that is not. The circuit shown is a very simple oscillator and can be assembled on a small printed circuit.

Circuit component list

  • 1 MPS6515 NPN transistor or equivalent (Q1)
  • 1 2N3905 PNP transistor or equivalent (Q2)
  • 1 1.2M resistor (R1)
  • 1 100K resistor (R2)
  • 1 18K resistor (R3)
  • 1 10K resistor (R4)
  • 1 1.8K resistor (R5)
  • 1 1uF / 16V electrolytic capacitor (C1)
  • 1 10uF / 16V electrolytic capacitor (C2)
  • 1 red LED (LED)
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