[Diy_efi] EEPROM based efi compter, DIY style.

[Bevan Weiss]

Hi Ben,

This certainly is most easily done using a microcontroller.
If you obtain a micro with ADC inputs then you can easily convert from 
an analog voltage into the digital domain, the micro can then operate on 
this to provide a pulse width modulated (PWM) output signal (either via 
dedicated PWM hardware, or through a software PWM implementation).

The main difficulty becomes conditioning the analog signal for input to 
the ADCs.  Things like O2 sensors don't have a very straight forward 
signal path and so additional control is required for them.
Most other sensors are relatively simple, being ratiometric to supply 
voltage, and hence only require an appropriate supply voltage to give a 
sufficient output signal.

An EEPROM chip itself is capable of very little, it certainly can't 
produce a PWM output unless additional circuitry is used around it.  I 
would strongly favour a microcontroller for this task.

With micros like the ARM7TDMI readily available for very cheap this is 
not a difficult task.

You would however want to pick up another programming language (C 
preferably, though some ARM assembler would likely be beneficial too).  
You would also want additional hardware development skills, but it would 
be an interesting project to learn on.

If you're just after something plug and play, then you should look more 
towards the megasquirt range that Bruce et al designed.  If you're just 
after the end product it's the way to go.  If you're after the learning 
then doing it yourself would certainly be enlightening, however I would 
caution that it will never be as 'easy' as you first imagine.


Regards,
Bevan


> Hi people.
>
> Just another of my less crazy ideas, I was wondering what it would 
> take to build a computer that can make a pulsewidth output based 
> primarily on a voltage (ie air flow meter).
>
> The idea would be to have four or five tables:
> 1: Air-flow/Pulsewidth (with pulsewidth the output)
> 2: TPS/RPM (pulsewidth output, overrides table one while rpm AND 
> throttle position are in range)
> 3: TPS change/Time (pulsewidth output, added to table one/two)
> 4: Temperature/Pulsewidth multiplier (simple warmup strategy, or a 
> master rich/lean knob)
> 5: O2/Pulsewidth multiplier (simple closed loop under certain TPS and 
> temp conditions)
>
> I can see this being a simple computer for converting naturally 
> aspirated engines to single point efi, with a minimum of wiring 
> required, primarily for economy.
>
> so how would you go about building something that can do this? My 
> electronics ability is limited to assembling kits and understanding 
> how simple components (transistors, capacitors, diodes etc) work, 
> along with limited BASIC programming. My main interest is in how to 
> program the EEPROM chip, and how to get the inputs to the correct 
> format (ie frequency is easy enough to do, but converting a voltage 
> into a digital signal is something I know nothing about). I am 
> presuming that an EEPROM chip can make a pulsewidth output directly 
> (with the aid of a transistor of course), is this correct?
>
> thanks
> Ben