Hi all,
Remember this discussion () a while back?
That's when I started a project involving a little travel trailer and trying to use a basic 4-wire wiring connection to properly light up separate brake and signal lights.
To sum up: the 4 wire connection from the car consists of: Ground, Marker lights (for night use), Left, and Right.
What that really means is that the brake and signal lights are combined in the 2 wires for left and right. Usually trailers just have a red light on the left and a red light on the right, and they do their thing.
But I bought fancy LED lights that separate out the brakes and the signal lights. Which left me trying to figure out if it was possible to do some logic to properly handle the brake and signal lights to their full potential... without rewiring the harness on the car!
I think I've found a way to do this using logic chips. And from what I can tell, the 4000 series chips will handle up to 18 volts, which is plenty to handle whatever the tow vehicle will throw my way.
I played around with it on this website I found (Simulator.io), and it seems to work like I want it to.
http://simulator.io/board/qQCIfvpreQ/3
1. If either the left or right wire is on, that orange indicator will go on, giving properly blinking
2. if both wires are on, the red brake lights go on, giving proper brake light function
3. if the brakes go on, the brake lights will remain on as long as there is power to the system (ie, at least one of the left or right wires has power)
4. if the brakes are on and one of the left or right wire goes off, then that indicator light goes one - essentially, the one side that's blinking will end up blinking but in reverse to how the car is blinking.
If you follow that URL above, you can play with the circuit - clicking on the "0" box beside the "Left" and "Right" inputs simulate the wire coming from the car.
I was going to test this using the 7400 series chips I have (using 5 volts and LEDs), but sadly I don't have any OR chips! (I'll have to fix that soon!). And making them from NAND chips looks to be very painful.
Here is my logic (edit: I had the wrong picture here earlier)
Special thanks goes to Michael Kellett michaelkellett for the idea of latching the brake lights ON and keeping it on until both wires are off.
And another special thanks goes to Douglas Wong dougw for the idea of putting together a logic truth table - that helped me get things straight in my mind, and gave me the idea to try using logic chips.
Anyway, what do you all think? Am I overlooking any potential problems?
ps, I think I also figured out a way to achieve this using just relays, but I figured solid state would be smaller and easier.
Thanks,
-Nico
edit: Note mostly to self: I have updated the trailer lights logic to now also reset when both blinker lights are off: https://simulator.io/board/qQCIfvpreQ/4
This allows the circuit to retain power and still function properly. The previous logic required power to be shut down in order to reset. The new logic allows battery or super-cap backup to keep it on.
