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Thursday, December 27, 2018

Adding an led blink light to a toy police car [simple solution with discrete components]

Unlike my other posts, this is pretty simple and is not using any micro-controllers. This one use just transistors/mosfets & will add a blink-light to a toy car :)  Alternatively i could have used an attiny13 to achieve the same results. But I will leave it for later

This is probably one of the simplest electronic project which everyone has tried/should try if they are interested in electronics. This is basically an astable multi-vibrator, controlling two led lights (RED/BLUE) and are triggered by forward/reverse movement from the rc remote. Once triggered the lights keeps running for around 30 seconds and then stops, saving the battery use.

The schematic for the project is shown below
A simple led police light with auto power off

The power supply is around 4.5 volt from the toy car and trigger  is connected to the H-bridge output for the forward/reverse motor (use a  pair of IN4148  diodes to get a positive edge from the motor)

Circuitry is the popular astable multivibrator.  Changing c1/c2 with higher/lower values will decrease/increase the speed of blinking.  Increasing the capacitance from the gate of 2n7000 to ground will increase the time left for auto power off after the last trigger.

Components list:

Parts list
if you wish to make a pcb, this can be done with the attached gerber files HERE or here for all other related files

PCB layout

And here are some snaps from the prototype

Connecting the trigger from motor outputs:

TRigger from motor output to gate of 2n7000 via IN4148 diodes

Hot-glued to the toproof

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