Separate Brake Light From Turn Signal

eTech said:

Resolving this makes a
solution more complicated. Detecting the state of static switches, like a
turn signal switch, or brake switch, is much simpler, but isn't useful for
the solution you want.

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ThomsCircuit said:

Awe man.
I did learn a bunch and for that i am thankful. Do you feel that the circuit member crutschow designed is viable? It is not that I doubt the design but there was a bit of confusion in the beginning as to how the circuit was to function. He indicated in post #42 the following which seems to be a problem that his circuit solves.

Crutschow said:
"It's not clear to me that any of the other circuits posted here operate properly for the combined signals of one side blinking and the other side steady-on, indicating a combined turn and braking situation.
Below is the LTspice sim of one that does:"

Your thoughts.

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crutschow said:

Here's the circuit powered from the turn-signal lights:
(The delay circuit causes an occasional extra brake pulse when the braking ends, such as at the 14s time in the sim, but that shouldn't be a problem to those following the vehicle.)

Do you know how much current the brake light takes?
That will determine the required current rating of the diodes.
(The diodes shown are 3A).

View attachment 145878

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eTech said:

Hello TC,
Sorry for the delay....I've been getting over the flu..

I found a problem with the circuit. When both brake lights are on (no turn signals) the third brake light flashes once, but should be steady on. I found this during a bench test.

The way to fix is to make some wiring changes, and use AND (1 chip) and NOR gates (1 chip), instead of the CD4048B. If there is another way to fix, I'm open to suggestions.

See below:

View attachment 147475



Notice that every time the brake is applied (either, or both, inputs steady), the 3rd brake light is steady on. The 3rd brake should only flash during emergency mode (both inputs flashing).

I still need to bench test this new circuit configuration.

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eTech said:

I've gone back and rechecked this circuit and it turns out I had a bad CD4025B chip. I must have zapped it

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shokjok said:

The unidentified trailer design may not need a third brake light

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