Truck
Trailer turn signal update
If anyone was interested in my trailer turn signal project, (there was a lot of haters on that one, esp. on Hackaday) Pacman left a comment on that post about an RV turn signal adapter for towing a car at etrailer.com. I bought one of these to try it out. Turns out it does seperate the brake signal from the left and right turn composite signal. So it would work for what I was trying to do. The only thing it doesn’t do that mine did was let the light also act as a clearance light. With my design, the light would be on if the clearance lights were on and flash off to indicate a signal. Not really a big deal though, because you can buy clearance/signal lights to replace the existing clearance lights and use both signals with the same light.
I wasn’t expecting much, but out of curiosity I milled off the top of the plastic box. You can see two relays sticking out of the epoxy potting.
Turn signals for a trailer
I’ve been working intermittently on a project to come up with a way to add turn signals to the side of a trailer without needing any extra wiring from the truck. The way people normally do this is by tapping the side markers into the turn signal wires. However, that makes the side markers turn on and off with the brakes which makes for a confusing signal. There is no shortage of patents for adding this type of capability, but they usually require a unique transmitter aboard the truck that communicates with another unique receiver on the trailer. Since the 6 pin standard is ubiquitous, that type of system will likely not be available or popular for some time. I didn’t want to add any special hardware to the truck either. So I’ve been working on a solution that taps into the trailer’s main electrical harness and creates an extra side turn signal for each side of the trailer and also functions as a clearance light.
You can use any standard clearance light and it will function as a clearance light when the lights are on, and also flash that light when the appropriate turn signal is on. The brakes will not cause the side markers to flash. You can add new lights, or simply intercept the wiring to existing clearance lights. The only modification is to the trailer, and it will work the same for any truck. The only requirement is that the trailer has electric brakes and the truck has a brake controller.
My code is running on an ATtiny24, on a board I prototyped just for this. I built an in-line harness for testing that passes the signals from the 6 pin connector to the trailer, but taps into those signals for the logic. My device has two standard LED clearance lamps attached as left and right turn signals for testing. This system is an add-on to the existing trailer wiring, so in the event of a failure nothing is compromised.
It has been tough getting this working, as there’s not exactly a manual for how the truck and the brake controller handle the signals. It’s taken a few months, as evidenced by the tarnished PCB. If I remember right I made it this summer.
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