I think I'll plan for both sensors, but as separate circuits, so say 24 thermo-couplers, and you choose where / if you want the fast sensors. It adds a feature of being able to monitor the temperature of misc devices to ensure they don't over heat. A quick story, I once was working with a low end motor controller, it has 12 FETs parallel driven. It had some supporting circuitry, but we buggered it. One end of the controller was closer to the motor, which caused that end get slightly hotter than the other end. The temperature compensation sensor was on the other end of the board. Once the FET closest to the motor overheated, it popped, which then caused the load to shift, which caused overheating, which caused a pop, ect down the line of FETs until no little FET's were left standing in a line. An expensive mistake because it only had one sensor. On this board I'd say a likely long term mode of failure is from overheating. One end of the case is visible and therefore exposed to the sun, what have you. It might be nice if we had some sensors telling us the case was getting two hot, or that some misc device was getting to hot. Thoughts?
mk e wrote:How big do you think the board is going to be?
About the board size, good question. I've stopped to ponder that a little bit, but have been putting it off until we had the schematics ironed out a bit more. By putting the discretes on top and bottom and breaking it into two separate boards with the brain stacked on top as a third. One board containing the power drivers, with injection, and ignition ect. The other with the lower power and lower voltages like signals in and signals out. Done that way I think the real space constraints won't be the PCB layout, but the heat dissipation capabilities. PCB wise, I think the 1 euro size we used for FreeEMS 1.0 would be about right. So that's around 7"x4"x4" ish. The key is can we get rid of the heat.
What's an acceptable case size? Perhaps we could have a remote case for staged injectors and some of the less common extras?
If we decide to go with a larger X,Y of the case, I might copy FreeEMS 1.0. FreeEMS was designed with SMT pads under thru hole components. This allowed easy bulk asm, while allowing blind DIYers. Takes a fair bit of PCB real estate, and is a 2 layer design. I like 2 layer designs when possible, you can get a scope on it, see burn or broken traces, ect. If I straight up copy that design, I would keep these modules. I think that FreeEMS has almost all of the most common features you want, except for the 6 cyl vs 12 cyl thing. Hmmm, I have to stew this over. Any objections about breaking this into two cases. Case 2 including thermocouples, staged injector drivers, and extra IO's. Case 1 being a 2 board layout, with 12 injector, 12 ignition, 2 RPM, 2 MAP, all the basic inputs including IAC and some of the extras we haven't drafted up yet. Basically case 1 is an OEM 12 cyl, and case 2 is the performance add-on. With this design, I think we can keep each case at 1 euro 7"x4"x4"ish. Perhaps case size is something we should bring up in it's own thread. Lots of possibilities here.
Um speaking of heat, I don't recall peak and hold injectors as a software bullet. Theory being, that you drive the injector hard for say 10ms, then you duty cycle the FET such that the injector solenoid field collapses and prevents the injector from heating up, ect. This allows for a more accurate turn off time, and it prevents pre-heating the fuel. We should probably add that to the bullets if it's not already buried in there.