Here is a pre lim design for a Maximite or Arduino
shield that off loads the EFI injector control stuff
to leave more time for EFIS. Four injectors each
can be set up differently. Once set up the engine
will run for hours with no processor intervention.
It use the CMOS 555 in PWM modulation mode.

Paul Lamar

Nice work Paul, a DAC running the PWM with it only receiving updates from the ecu.I do not think it will unload duty from the ecu, the ecu is still generating the signal to the DAC, plus monitoring all the inputs i.e. rpm, temp, afr and such. If you wrote in a condition to the loop that it only sends updated signals from steady state it would just load up the processor with more code to act on.

The external board is what I am also doing but the board can also run the ignition and injectors without the ecu. I have changed the design a bit to include opto couplers to protect the ecu and the driver boards, with logic controlled SSR's that default to the crank signal to the driver boards in case of failure of the ecu for any reason.

I have ran it on the bread boards being driven by the aurdino and it works good in simulation. The new boards are ready to prototype but it is going to have to wait a few weeks.

Oh here is a nifty little project I did this las week one evening after dinner. A very small compact Oscilloscope, I have been using to check injector scheduling and duration during the simulations. They are a kit from Sainsmart, $22.00

Davd Jr.


The DAC has four 8 bit latches. When you send them a byte the related
 DC output  voltage stays constant until you change that byte. This gives
pulse witdh resolution to one part in 255.

The PWM 555's get a trigger pulses from the CAS so as long as the engine is turning
over fuel will be injected. I will add ignition circuits that will put out the required
4 ms dwell pulse for modern coil on plug ignition  systems. Plenty of room
still on the PCB shield for that.  Basically four more 555's in  one shot configuration.
That will require attention form the processor every rev but the code is simple
and short.

Paul Lamar


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