Adding led brake lights

[tourist]

Mine aren't running too hot.  We'll see after the project is completed if I need the led brighter.

Finally got the circuit board  done and tested.  After a couple of days and countless tries finally got the traces to transfer to copper.  Drilled holes, mounted stuff.  Just looking around the house for hook up wires.

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[merold]

I need to build a circuit to detect when the brake lights are on and the turn signals on.  The brake light and tail light are the same bulb.  The tail led light uses 2.4 volts then when the brake is applied the voltage increases to 13.8 volts.  This circuit seems to work on my test board.  When the input is 2.4vdc the leds are on at about half the brightness and when the brake would be applied and the input is 13.8 volts the leds are on full.  The input only has two values: 2.4vdc and 13.8vdc.  These components are just what I had lying around and I think I would use a different op amp in the final circuit because I will need to monitor 4 different lights, (2 brake and 2 turn signals)  The turn signal circuit differs by reversing the 10k and the 100k resistors.  The turn signals input is either 0v or 13.8 vdc.
I read out here that the 741 isn't good to use in automotive applications, idk.  I'm open to better components or design but I can't draw too much current from the light circuit because it is monitored in some fashion by the onboard computer.  Any help would be appreciated Thanks.

that's so cool.. sir..
I wonder how can i easily troubleshoot the defected of that??

 

[audioguru2]

I read out here that the 741 isn't good to use in automotive applications, idk.

It is an antique that is 44 years old and only used by old teachers today.

I'm open to better components or design but I can't draw too much current from the light circuit because it is monitored in some fashion by the onboard computer.

The lousy old 741 opamp has inputs that do not work when they are anywhere near 0V or the positive supply voltage. Its output does not go low enough to turn off the transistor. It is too slow to follow the PWM pulsing.
I would use a low power MC33171 opamp or normal power MC34071 opamp. Their inputs work perfectly at 0V and their outputs go down very close to 0V.

Your LEDs are shown backwards.
Since your transistor is an emitter-follower then the 1k resistor at its base should be replaced with a piece of wire.

 

[Hero999]

Forgive me for butting in, I've not had time to read the entire thread.

I notice there are lots of LEDs connected in parallel; why? It's more efficient to connect them as three strings of five or even five of three.

If all this does is buffer the PWM signal then why use an op-amp IC? A comparator such as the LM311 or LM393 would be a far better option.