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For discussion of Speeduino compatible boards designed / built by other members of the forum and for guidance around making such a board
By tooly
the purpose of this deisgn is not to go with paired injectors. the goal was to make it cheap and small as possible up to 4zyl. you can read the project outline on page 2.
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By chaoschris
PSIG wrote:
Fri Jan 15, 2021 2:59 pm
A shunt diode solved the overheating, which indicates that flyback energy through the body diode was a substantial source of the heat.
the 3 outputs with (potentially) larger inductive load (Fuelpump relay, Fan relay and Idle Valve) are already eqipped with a diode to cut the reverse induction and prevent overheating of the diode in the mosfet. So i'm pretty sure it will work , but I will try to find a valve to check this out.

But hey, we are talking about a super-cheap ECU with integrated wideband controller in the estimated range of 45-50 Dollars (with connectors and pins, quite full assembled pcb, not a complete DIY). For this well reasonable price it should be clear that there can be some disadvantages or things that won't work. In some places of the world you can easily spend more money on drinking beer or mineral water going out one evening comparing to the price of this little ECU... :mrgreen:
Best regards,
By TR6
"U$7 34P" is in the part list of the board.


6437288-1 (on board)


User avatar
By chaoschris
Hi Carsten,
this combination looks fine. You have to be careful to buy the correct mating parts as there exist different codifications (COD1 and COD2).
I bought some cheap chinese knock-offs on aliexpress for 8-10 Euros (mating connector and header, pins and shipping included) . They also look fine and if you have any doubts about quality you can also use genuine female pins in this housings.
You will also need a really small crimping tool for these pins and you cannot use wires thicker than 0,75 mm2. The larger cables wouldn't fit through the housings and using 0,75 mm2 is already a bit annoying, depending on the thickness of the insulation of your cables (FLRY is recommended). I would suggest to use 0,5 mm2 cables, they are absolutely sufficient for the intended use case with active ignition coils (and also for the power supply).
Crimping these pins is in my opinion also a bit fiddly/tricky if you are be used to crimp junior timer pins or something similar. First time crimping these pins really feels like a kick in your a**.... :lol:
Best regards,
User avatar
By Chris Wolfson
Convenience is one thing, where one might save a few steps on a low cost product. On the other side, where function or reliability is put in question, there should not be shaved a Cent or two.
You should put the price of a diode, which is incredible low in production or bulk buy, into perspective to a failed MosFet because of a diode missing. Even if it will only effect 15% of ECU buyers. A part missing on a critical position is no question of taste, but a failed construction instead of a good one. Ask potential buyers of a product what they prefer: To pay 2$ more or except 5 parts missing, even if these can (theoretically) be added externally at low cost.
In the real world, 98% of users will first burn an ECU before fitting external diodes. Make things you sell idiot proof or you are one yourself.
User avatar
By chaoschris
Hi namesake,
we are only talking about the four mosfets from the injectors. The other outputs with (possible) inductive load already have a flyback diode to protect/relieve the mosfet.
Have you ever seen a ECU with flyback diodes in parallel to the injectors?

I will test the design with two parallel injectors on one injector channel (for which it never was designed) and also in harsh conditions like extreme temperatures with 80 degrees Celsius.

By the way, the additional price for the four flyback diodes (already assembled) would be only 3,72 US-CENT. Price was never an argument for leaving any parts away, but space is rare on this design and one of the goals was making this as small as possible. And totally "idiot-proof" as you called it is quite impossible on such a small design. But this was never the aim for it.
But the price is cheap, which allows you to learn it the hard way without loosing all your money at once..... :mrgreen:
Best regards,
User avatar
By Chris Wolfson
If you do not have the room to fit diodes, you can not fit them. I was so naive to think all MosFet switches would need one. Many MosFet I know have them build in, anyhow. Could that be a solution?
If not and a diode in some (rare) cases can be useful, put a warning and detailed installation instructions for external ones in the manual. Possible parts, diagram, a picture etc. That is all you can do.

Sure, idiot proof is impossible with electronic DIYS parts, but any chance of blowing something in regular, intended use should be eliminated. That was my point.
Personally I do not like to small designs, but here I see the price point, off course.

The basic idea to offer such a low price ECU is still great. It is where MS once started. Today the price of of the finished MS product is 90% profit. Even as I understand the need for people around the MS to make money, it´s price does not reflect the value of the aged product. So please go on with your project. It should have a great future, as long as you stay sub 100 US$. Also, the lower the price, the safer you stay from copy cat´s.
Tuner Studio as a standard software is the other key factor to it working. Today I would not buy any ECU product with another software. Try to get W10 software for an older, programmable ECU and you know what I mean. I learned it the hard way...
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Chris - then very good. I look forward to buying and trying your finalized product. Suitable engines for this control show-up fairly often.
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By chaoschris
Chris Wolfson wrote:
Sun Jan 17, 2021 2:12 am
If you do not have the room to fit diodes, you can not fit them. I was so naive to think all MosFet switches would need one. Many MosFet I know have them build in, anyhow. Could that be a solution?
Hi Chris,
there it is, the classical misunderstanding..... :D
The used Mosfets already have a integrated body diode (max reverse current 2A).

AO3400A.png (48.24 KiB) Viewed 333 times

I was talking about the external flyback diode (parallel to the inductive load). In most cases it is always better to eliminate the inducted reverse energy direct on the source.

Using flyback diodes parallel to the injectors would also affect the timing as the switch off duration would be longer and could interfere your injection timing. The inductivity of the injectors isn't too large to cause severe problems with that mosfets. But further tests will be done for sure....

Chris Wolfson wrote:
Sun Jan 17, 2021 2:12 am
It should have a great future, as long as you stay sub 100 US$. Also, the lower the price, the safer you stay from copy cat´s.
We want to stay at less than 50 US$ for the complete ECU with connectors if this is possible. And the primary goal is not to produce them for the masses. We will release all sources that everybody could produce them easily direct by his own or some people order them together. Or somebody else will produce them. We aren't afraid of copy cats as it is intended that others will produce them. This is no design to generate money, it was made for the public!
The last batch of 5 quite full assembled prototype pcbs was only 135 Euros, shipped and taxes already paid by the producer. And the more you order, they will get cheaper. In the minimal batch of 5 pieces the revision 0.0.6 was something around 27 Euros per pcb direct to your home.
This was the primary goal of this ECU, a cheap thing that works and you can use in most use cases with a maximum of 4 cylinders and already integrated wideband controller. Not more and not less.

Best regards,
By JHolland
You do not want flyback diodes on the injector drivers, you will get horribly slow turn-off times, injector drivers should always avalanche.
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