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Pulsing Third Brake LIght Problem. ( whats wrong with this cct ? )

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Hi i make this cct. And its working as usually ( some blinks and then continuously on ) when i connected it to my PSU ( 12V ).

And then i connect it to my car it doesn't give me any damn blinks. ( its happend only when engine starts )

My car voltage is 13.8 - 14V

Whats wrong with this cct ?

What r the changes that i have to do ?


Plz help me coz im sick with this cct:confused: :mad: :eek:

**broken link removed**

This is the link for main site
**broken link removed**

Thank you very much:) :)
 
Car alternators produce high voltage spikes. So I expect that these are affecting your circuit. It is a wonder why they have not damaged the IC.

I suggest that you connect a 1 k resistor in series with the +12 Volt line to the left of R9 and a 9V1 Zener diode from the other end to gnd.

So R9 and Q2 remain connected to the +12 Volt, but the rest of the circuit is supplied from the 9.1 Volt line.

I also suggest that you connect a 220 uF elecrolytic capacitor and a 100 nF ceramic cap in parallel with the Zener.

These will regulate the supply to the IC and suppress the spikes.
 
The entire circuit is supposed to receive its power from the brake light switch. +12V is not supposed to be connected continuously to any point in the circuit. **broken link removed** explains this.
 
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