Separate Brake Light From Turn Signal

[ThomsCircuit]

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.

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.

 

[eTech]

Only way to know is if all states are checked.
Another state to look out for is when removing brake, the third light delays a half cycle.
It should also handle the "emergency" state where both lights are flashing.

Just a heads up, the simulation can be misleading..

 

[eTech]

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.

Crutschow's circuit uses a latch, which may or may not be ok. I thought about using a latch of some type in my circuit, but was concerned with a circuit failure causing the 3rd brake light to suddenly latch "on". Another thing that concerns me with this whole idea is the possibility of a circuit failure causing the brake light to suddenly come on, and, in turn, causing an emergency application of the brakes by a following vehicle (potentially causing an accident). Please advise.

 

[eTech]

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

Hi Crutschow,

I'd like to play with this circuit. I can redraw it in LTspice, but I'd rather just use a copy of your .asc file. Can you post the .asc please?

 

[eTech]

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.

Hi TC

I've gone back and rechecked this circuit and it turns out I had a bad CD4025B chip. I must have zapped it. Anyway, the circuit works as intended. I did make some minor mods though.
I removed D10 and R4, not needed. Changed Rx1/Rx2 to 150k each to match the flash period of 705m Hz.

 

[ThomsCircuit]

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

What awesome news. Thank you.

 

[shokjok]

The unidentified trailer design may not need a third brake light ( aka collision avoidance light in Canada). 1986 model year vehicles sold in Canada were the first to get this additional taillight. Tall trailers got it in the 1990's, platform trailers and tow dollies don't need it.

 

[ThomsCircuit]

The unidentified trailer design may not need a third brake light

Correct. It does not need one. It's a simple 4x8 single axle. I just liked the idea of adapting the trailer with a third light.