The plan is low side switches for the fuel injectors, that means switching the ground. They used to do high side switching and made special parts for that but that was some time ago and now the auto industry has settled on low side switches. All questions are welcome here though.
Russian2, for me this is not about the process, I am focused on the result - to produce some ECU boards. I think the best way to do that is to produce and use your work as soon as possible. I am trying for some re-use, so I am not sure what you mean by "re-using at least some of the to-some-extent tested components"? I am likely unaware of many things. So at one end my project is using a Freescale evaluation board for software and some initial testing and at the other end I am drawing schematics and doing board layout. I would show this stuff more, but I don't know how to get the schematics into a PDF since the tools are running on Windows and I am almost completely ignorant about that.
I am currently planning on using the Freescale MC33810 chip to drive the injectors and coils. These chips can drive 4 channels of each and I will likely put 3 on the board.
Here is a description of the issue with the voltage spikes. I think it is an issue of old cars vs. new cars and also cars designed as a unit by a factory compared to cars built in garages. Also possibly I over design things
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Cars have powerful alternators. They store a lot of energy while they are running. If you have questionable wiring to the battery, if it ever becomes disconnected, if you ever turned off a master or battery disconnect switch on a race car that's running, and perhaps a few other things - you can get something called a "load dump". The standards for this are like 100V for a half second, potentially lots of amps too. Modern cars handle this in the alternator of voltage regulator. A vintage car not so much...
So at the moment I am thinking I will not depend on some other piece of equipment in the car to do this for me. Someone could easily buy this unit and put it into a car that used to have a carb. and get into trouble. I looked at a reference design for these chips and it had a device to help with this but it would have depended on a larger unit somewhere else in the car to prevent a crater from forming where that device used to be
The unit I am thinking of putting on is rated to handle these load dumps. It's a couple of dollars and it will also take probably a larger wire size. These are rare events though and they don't last long. I only need about 1 Amp to run the ECU, but the wire needs to handle a big burst for a bit less than a half second.
Another thing is that I think the ECU needs separate ground wires for the electronics and injectors and coils. People have been telling me you can't put the drivers for the coils in the ECU box, but I would like to try and get that to work. If nothing else it may look like one box on the outside and more boxes inside. At least covers inside over different parts of the board to keep things electrically separate.