[joey120373]

Have been busy at work for past week or so, but I may have more time to put into this.

Not sure about that coil but it’s easy enough to test, I would be interested in seeing a lab scope screen shot of the signal the stock ECU uses for the coil control, that would give the dwell time for the coil. But some small engines just use a flying magnet on the flywheel to generate the coil input signal, and I have no idea if that type of coil would work with a modern 12v IGBT driver.

As far as putting components on the back, yes, that is doable. In fact it could make for a much more compact board, and also allow for better thermal performance.

My current thinking is to populate one side of the board with all the fine pitch, hard to solder stuff. And put most, if not all of the bulky ( easy to hand solder ) stuff on the back. Since this is will be bolted to a large chunk of aluminum , that could be used as a heat sink, win win.
And on those lines, a standard liner regulator would simplify the design and allow for a cleaner power supply.

I went with a buck converter in the current design because I have concerns about heat, the board pictured will be potted inside an enclosure so it’s completely waterproof. There is no guarantee that it will be able to shed the heat generated by a liner regulator, so I went with a buck converter module and added some LC filtering that I hope will keep the noise under control ( have to test that still) .
So for now, and this is likely to change, I will start putting together a board design that has 2 injector drivers ( for 2 to 4 high impedance injectors ) 2 coil IGBTS
minimal analog inputs and the Magnetic on board TPS sensor IC thingy doohicky hootis-Mubob. A coupe of low current low side relay pouts and that should do it.


In the next few days, hopefully, I can post some 3D renderings and get some feedback.
Joe

[PSIG]

Not sure about that coil but it’s easy enough to test, I would be interested in seeing a lab scope screen shot of the signal the stock ECU uses for the coil control, that would give the dwell time for the coil. But some small engines just use a flying magnet on the flywheel to generate the coil input signal, and I have no idea if that type of coil would work with a modern 12v IGBT driver.

There are a couple ways to determine coil characteristics and optimal maximum dwell performance. One is to 'scope the coil current through a shunt (0.1 ohm 10W) for amps, noting the point that the current "bends-over" and saturation is mostly complete and coil heating skyrockets. Another is to test the coil characteristics (primary and secondary resistance, impedance, etc) and run the calculations for dwell at your specified voltage.

Re-test or re-calculate at other voltages in order to create your dwell voltage correction table. With dwell corrections, there is no reason your spark cannot be as strong at 9V as at 15V (or any other reasonable voltage). This can help at many points, but especially during starting, or when running off of battery-only.

[JHolland]

That looks like a CDI coil, that probably won't work well with Speeduino.

[jbiplane]

and the Hall effect TPS.

Hi Joe. Please estimate as option contactless magnetic sensor instead of external TPS
https://youtu.be/_RlguxPV8TQ

[joey120373]

I estimated the post, I am somewhat familliar with that IC, or a variant of it, years ago I ordered a small dev board and played with it for a bit. Not sure where it is now but I’ll have to see if I can dig it up.

[PSIG]

I would take care to avoid obsessing over the TPS options of mechanical potentiometer (typical TPS driven directly by the shaft), versus Hall and magnetoresistive (MR) position sensing. I would test and consider all of them for your best options, as the complications of MR or Hall (especially custom configurations) can often outweigh the simplicity of pot adapters.

For examples, the project could possibly be simplified by using a proximity sensor for the throttle arm, cable tab, or servo arm, or a linear pot clamped on the throttle cable or stuck onto the throttle servo, or sensed from the servo position signal without any throttle shaft sensing (ask the servo or throttle motor or controller/receiver where the throttle shaft is positioned). Many, many options that may be more universal for application.

David

[joey120373]

5cmx5cm board, most components are placed but no traces run yet. Just getting a feel for how it might be laid out.

board looks like it might be feasible, given a good thermal heatsink.

[jbiplane]

5cmx5cm board, most components are placed ... might be feasible, given a good thermal heatsink.

Wow Joe ! Looks very good and promicing. If I will get one day will mill nice Throttle body for, make intence testing including thermograms. Did you estimated magnetic TPS sensor on back side?

BTW what software do you use for PCB design and tracing ? Altium have very nice automating tracing sawing a lot of time.

I would test and consider all of them for your best options

Thanks David. Having bulletproof contactless TPS very benecifiar for this project.

[joey120373]

Wow Joe ! Looks very good and promicing. If I will get one day will mill nice Throttle body for, make intence testing including thermograms. Did you estimated magnetic TPS sensor on back side?

I was initially planning on putting a spot for the magnetic TPS sensor on the back side, center of the board. I need to get that drawn up in the schematic .

Still a lot to do, need see if LCSC has a surface mount MOV for the input protection. I used an 0402 sized one on my other board but that hasn’t been tested yet, would feel more comfortable with a larger 1206-1210 sized unit that matched the speeduino specs better.
also need to figure out what type of serial interface would be best, the Standard “ pro-mini/FTDI” ) pin interface would take up a huge amount of space. I could try to squeeze a cheaper USB>serial circuit on there to but again that’s a good chunk of board space. Smallest would be a 3/4 pin header interface, rx,tx, ground and a reset.

I also may get rid of the muti turn trim pot for the max9924 in favor of a smaller SMD type trimmer.

This boards has no IAC control, though I think there is room to put a medium current driver or two.

I am using KiCad to draw this up.

[joey120373]

One thing that worries me and needs to be tested though, is the coil drivers. This is a an IGBT that I have not used before, and it remains to be seen what the thermal issues may or may not be. In years past I have used the bosch BIP 3xx TO220 drivers to drive coils, and they had no real thermal issues at all, so I am hoping that is the case with these.

I can give them a thermal path to the mounting hole easy enough, as I did with the liner regulator, but that would electrically tie the coil ground to the main ground and I would prefer to keep that separate.