A thought...

[tom cloud]

>I'm thinking of putting fuel injection on my pontiac 455 in a '78 trans am.
>
>I'd like to buy the 900cfm throttle body from holley that already includes:
>1. 4 injectors, 85lb/hr (kinda like a tbi 4 barrel)
>2. tps

This is essentially my direction for my old Bronco -- except I bought
the whole kit & kaboodle from Holley (the 2 bbl 670 cfm).  It works,
but I thought I could do better.

>All I'd need is an interface to these four injectors, a computer, couple of
>sensors (map, temp, ego, etc).
>
>I'm thinking, instead of going the 68hc11 route, using a pc.  Instead of
>building a a/d and d/a board, use two parallel ports.  That would give me
>8 ins and 8 outs.  Timing would be resolved by the computer, hell, 386/486
>motherboards are cheap.

Sure would be big.

>Question 1: Am I crazy? Anyone see an inherent flaw in all of this?

I used to use PC (understand the word PC was around long before IBM
got into it -- back when MITS, IMSAI, etc were making 8080, 8085, &
Z-80 boards) motherboards for dedicated apps.  They were very
reasonably priced and had lots more power than I needed -- but,
they were lots bigger than a specially designed board and usually needed
bigger power supplies.

>Question 2: I need a good power supply to give me +12,+5,-5,-12. Should I 
>pull the car's power, use a 12/24 volt transformer, then get a couple of
>voltage regulators to give the voltages I need? Car voltage lines are 
>extremely noisy, any ideas on how to clean the signal?

>From that question I deduce you need a little help.  You can't get
the other voltages from the 12 volt supply without going through
an inverter of some sorts -- a transformer only works with AC and
then only with a limited, specific frequency range.  The transformers
you are used to work at 60 cycles / Hertz.  Aircraft transformers
work at 400 cycles (they can be smaller at higher frequencies).  If
one knew how, he would build a high frequency inverter (like 50 to
70 kilohertz) and go from there (it's what's in all the current PC's,
it's called a switching power supply).

[In fact, while I think about it, one could take a standard PC
switching power supply that sells for about $30 and modify the
transformer and switching portion to operate off 12 volts.  See,
the supply in your PC rectifies the 120 VAC from your house to get
about 170 volts DC and then switches it (turns it back into
high frequency AC) and puts it through one or more transformers to
get the different voltages desired.  The car already has DC -- it's
just 12 volts, not 170.  All that should be required would be to
rewind the transformer(s) and beef up the switching transistors
to handle the higher currents.]

Note that the PC motherboard may not need anything but +5 volts.
The +/- 12 is for the RS-232 ()serial) and +12 is used for the
disk drives.  I'm not sure if the -5 is required anymore??
If one of the voltages other than +5 is required but needs small
currents, there are chips that use only capacitors (not transformers)
designed specifically to generate low current bias voltages.

>Question 3: Any suggestions, ideas, or people interested?
>
>Arnaldo
>aec at ao.net

Tom Cloud <cloud at peaches.ph.utexas>

None of the opinions expressed here are mine or anyone elses