[PSIG]

Then another option is to simply cut or disconnect the COM pin on the ULN chip. This prevents the back-feed issues, but deletes the diode protection. Alternatively, add a 15V or 18V Zener diode to the COM output so power does not back-feed from the resting battery, but voltage spikes are still suppressed. Your call on any of that.

David

From the datasheets:

ULN_backfeed.jpg (86.38 KiB) Viewed 12258 times

[pazi88]

Thanks! That's one way to do that also.

I did found that I have bunch of leftover 2n2222 transistors so I'm thinking I will add one of those into the circuit. So that the collector connects to the main relay coil, emitter to ground and base to the 12v from ignition switch with resistor in between. This way the main relay should turn on when the ignition is turned on. And also switch everything off when there is no power from ignition switch. This way I can again use the 12v input form main relay to power on speeduino and run it to uln com pin without problems. And also I don't need to use the fuel pump output to switch the main relay also.

[Raku]

i made a little pcb for controlling bmw main relay, tacho and ac. you can use the schematic on your PCB.
https://github.com/Raku5200/speeduino-B ... ion-module

[cmjdevco]

I just put a small resistor/transistor circuit on board for MREL circuits.. Never had an issue.

[pazi88]

i made a little pcb for controlling bmw main relay, tacho and ac. you can use the schematic on your PCB.
https://github.com/Raku5200/speeduino-B ... ion-module

That's exactly what I did do with 2n2222 But well I think it's now time to get the actual PCB manufactured.

[pazi88]

Just placed order for the boards. Hopefully I don't have mistakes there

Finished product:


I did some tidying to the traces, added some stitching for the ground planes and some text here and there. It's not perfect but maybe good enough for first try.

[janithdg]

Hi Pazi88,
i think by using unused io's of the mega, it should be possible to have 6 inj seq fuel
and this it will be cool if flat shift input and fan control outs in a separate socket

[pazi88]

Hi Pazi88,
i think by using unused io's of the mega, it should be possible to have 6 inj seq fuel
and this it will be cool if flat shift input and fan control outs in a separate socket

Yes, but that would require code changes and I'm not currently capable of doing those. Maybe in future But I don't know if mega has the grunt to drive 6 cyl sequential. But on the other hand I see people using teensy which should be capable of doing that. And doing sequential in m52 would require the cam sensor to be swapped to hall one from m52tu for example. The stock m52 cam sensor is weird one relying on phase shift of 120khz sine wave.

And the launch, o2 input, fan and boost control out are in the separate socket at the back. I did also run the fan control wire to the pin at 88pin connector that should turn on the factory electric fan.

[dazq]

Hi Pazi88,
i think by using unused io's of the mega, it should be possible to have 6 inj seq fuel
and this it will be cool if flat shift input and fan control outs in a separate socket

Yes, but that would require code changes and I'm not currently capable of doing those. Maybe in future But I don't know if mega has the grunt to drive 6 cyl sequential.

Not so actually, you could have 6cyl seq fuel OR 6cyl sequential spark with a mega, but not both.
There are 9 channels available, you need one for the vvt? So that leaves you say 6 fuel and two for spark(wasted type) or 6spark and two for the grouped fuel.
Full 6+6 will come in the future so preparing the board and perhaps adding jumpers to select the channels might be good advance planning/design

[pazi88]

Not so actually, you could have 6cyl seq fuel OR 6cyl sequential spark with a mega, but not both.
There are 9 channels available, you need one for the vvt? So that leaves you say 6 fuel and two for spark(wasted type) or 6spark and two for the grouped fuel.
Full 6+6 will come in the future so preparing the board and perhaps adding jumpers to select the channels might be good advance planning/design

Oh ok, so it's more like not enough outputs problem? But when that is available, I will probably do another board design to make that happen.

But correct if I'm wrong, but there is 15 PWM outputs from mega?

1-12 would be for fuel and spark
That would leave:
13 - boost
14 - idle 1 for 3wire PWM
15 - idle 2 for 3wire PWM

VVT is slow on/off type in these engine so non-PWM output is fine. Does tacho output need to be PWM? If so, there could be extra circuitry to drive 3wire PWM with one output, which is not problem.