Separate Brake Light From Turn Signal

I received my boards today and realized there was a tiny issue. Copper Pours have a solder mask. I should have selected a top layer Pad without a hole. I improvised but i'm sure you fellas would not approve and I don't blame you one bit.

I've seen it done before. Not ideal but do what it takes to get it going. They call it "cobbling together" and DIY for a reason.

Dont use sandpaper because it will thin out the copper. Use a razor blade (or razor knife) 90° to the board and scrape the solder mask away. Do an area slightly larger than the heat sink so the heat sink sits flush to the copper.

ZipZapOuch said:

Do an area slightly larger than the heat sink so the heat sink sits flush to the copper.

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thanks man.

ThomsCircuit said:

thanks man.

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How hot is the FET going to run?, unless it's getting excessively hot there's no need to remove the resist, it will reduce the flow of heat in to the copper, but if the FET isn't running hot then it doesn't matter.

I'm just assembling a board at work, this has an FET mounted horizontally, as well as two LM2585's, I don't have copper underneath them, nor mounting holes - originally I had a mounting hole, plus a small finned heatsink, then I realised they weren't running particularly warm, so I dropped the heatsink in the next PCB revision.

I can see your reasoning (I did similar), but have you actually tied it just on top of the resist?.

Nigel Goodwin said:

How hot is the FET going to run?

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I don't think it will get hot at all but that is me guessing. The output is a strip of about 15 LEDs.
I thought I had it documented somewhere. I did find it on page 4 of this post.
0.134 A or 1.5mA. The design and the time I spent measuring and all was a valuable lesson as everything lined up perfectly.

When I was submitting the files to JLCPCB I noticed the shipping almost tripled from . I told the fella in the chat room that it was higher than I could justify. I thanked them for the years of service and went on to check out a few other outlets. About a day later I got a coupon that covered the entire project. So with it I got (3) separate projects (20 boards total) for less than $10.00 shipped.

Then why waste time cleaning the resist off? - just try it and see what happens, and to be honest the small piece of copper underneath is very small and a poor heatsink anyway.

A microcontroller can be eliminated by subbing analog switches wired as an XOR circuit.
In my trailer brake controller circuit ( found in another historic thread), relay center contacts connect to separate tail light feeds. The relay coils are fed from one of three toggle switches, sharing a common positive feed. All relay coils share a common ground. The flasher input is fused from the positive supply, and the flasher output feeds into the NO turn relay contacts. The brake switch feed connects to the NC contacts on the two turn relays only. The reverse relay is wired as a high current SPST switch to the reverse lights.
Fewer parts makes for a simple circuit.

shokjok said:

A microcontroller can be eliminated by subbing analog switches wired as an XOR circuit.
In my trailer brake controller circuit ( found in another historic thread), relay center contacts connect to separate tail light feeds. The relay coils are fed from one of three toggle switches, sharing a common positive feed. All relay coils share a common ground. The flasher input is fused from the positive supply, and the flasher output feeds into the NO turn relay contacts. The brake switch feed connects to the NC contacts on the two turn relays only. The reverse relay is wired as a high current SPST switch to the reverse lights.
Fewer parts makes for a simple circuit.

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Post a schematic if you have the time to sketch one - this question has been raised multiple times.