Seeking advice for wiring project - LotusTalk - The Lotus Cars Community
 
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post #1 of 8 (permalink) Old 06-08-2019, 05:55 AM Thread Starter
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Seeking advice for wiring project

I am trying to make an ECU breakout box that allows me to intercept and replace wiring harness connections without permanent modification of my car's wiring harness.

In order to do so, I created drawings of a container to hold an ECU header and a PCB layout which could contain the header and connect it to screw terminals. The screw terminals would allow me to reversibly replace connections to the wiring harness along the path to the ECU.

I spent a lot of time figuring out how to perform toner transfer in order to etch the PCB. Nevertheless, I am still failing to produce a good part. I find it very hard to etch far enough that the leads are not shorted to each other while also stopping the etch before some of the leads are opened to discontinuity. Could this be due to my etch control? Could it be due to my PCB layout? Is there some other change that would help produce the PCB pattern that I want?

If you have any experience creating a PCB layout or etching a PCB, I would be grateful for any insight into making my project succeed. Does the wiring layout look okay (wire thickness, inter-lead spacing, wire routing path)? Does the transferred etch mask look okay? Similarly if you have any constructive feedback for the overall plan, please let me know.

Thanks,
-David
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post #2 of 8 (permalink) Old 06-08-2019, 06:09 AM
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First of all, PCB repair is simple, solder a piece of 26 ga[or like one strand of a larger stranded wire] and carry on. Trust me, some of the highest tech stuff you can imagine has pieces of wire soldered on for repairs.


I have a feeling you might be concerned that the whole thing is a bit thinner than it ought to be.

Is the board high quality?

Is the acid the correct thing, just a quick glance calls out Ferric Chloride.

Since there is no solder mask on this I would fix the errors, and solder over the whole thing and call it good.
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post #3 of 8 (permalink) Old 06-08-2019, 06:11 AM
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I haven't etched a PCB since I was in high school, many many years ago. I take it that you are only making a one-sided board so that you do not have to figure out how to make the barrels. Also, drilling the holes is PITA, too.

My suggestion is to use this board house, https://www.4pcb.com, because they will do small runs, 5 pieces, at a very reasonable price. You'll have your board in about a week. I use them quite a bit to make small and large runs of PCBs.

Later,
Eldon
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post #4 of 8 (permalink) Old 06-08-2019, 06:13 AM
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Also if the ground plane is not required for noise, you could probably get thicker runs in there which might be more reliable
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post #5 of 8 (permalink) Old 06-08-2019, 06:30 AM
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I can not help with the engineering of this project, but would like to be sure of what you are trying to do.

Is this to make it easier to remove/replace the ECU, with less chance of messing up the many fragile connector pins the stock harness has?

Anyone can make something complicated. It takes genius to make it simple. Einstein.
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post #6 of 8 (permalink) Old 06-08-2019, 06:35 AM
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I dug around, you can buy 2 oz copper, where mostly you see1 oz, which might be more tolerant of less than perfect process
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post #7 of 8 (permalink) Old 06-08-2019, 07:05 AM Thread Starter
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Thank you all for your comments.

I may give the PCB repair a try; I'll have to see if I have a steady enough hand to fix traces without accidentally soldering everything together. I am certainly worried that the traces are too thin, too- even though they are very thin within the ECU, I expect that power transmission or signal quality will degrade if I make the leads minuscule.

When I bought the CCB, I did not even realize that there were different quality or thicknesses available. I just bought something with a low cost and a large enough cross section to satisfy my design.

I chose HCl as the etchant over Ferric chloride since it is supposed to be recyclable (and proper disposal of ferric chloride is troublesome). Also, I like the emerald green color of the CuCl2 solution.

My plan for a single sided pattern is the result of trying to keep the design simple. In the ECU, there are multi-layered connections (allowing for greater area to get between the PCB and the ECU header). I don't think that I have the capability to create vias and buried traces, so I'll just solder on the opposite side of my headers and terminals with a single-plane pattern. I have access to a jewelers drill press, so I was not anticipating too much trouble with creating the through-holes: just a bit of tedium.

In the mean time, I've submitted a request for quote to 4pcb. I'm trying to keep this cheap, but I've used a few months of hobby time just trying to learn to transfer a toner mask (as well as buying supplies for this, on the order of $50-$90 of transfer paper and transparency paper, PCB mask, copper clad board, etch chemicals, etc.). It may have been cheaper to simply order from a PCB production house from the beginning.

My intent with this project is not to make ECU access easier, rather, I am interested in treating the ECU as a microcontroller that I can play with and augment, much like an Arduino. For instance, the T4 has two unused analog input pins, so I am planning on directly connecting a TMAP sensor as well as a linear oxygen sensor (as opposed to the OEM logarithmic response sensor). I have not checked, but I also expect that there are digital IO pins available. There is a lot of unused flash memory available for patching in code, so I will be able to play around a bit with engine monitoring and controls. The OEM wiring harness is very expensive, so I don't want to permanently modify it.
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post #8 of 8 (permalink) Old 06-08-2019, 07:11 AM
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Originally Posted by Obeisance View Post
Thank you all for your comments.

In the mean time, I've submitted a request for quote to 4pcb.
You can get quotes immediately On-Line from 4PCB. If you need help creating the correct files for them, PM me and I'll try to help you out.

Later,
Eldon
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