Idle stepper motor

[Ludis Langens]

Jose Carlos Rublescki <rublesck at portoweb.com.br> wrote:
> I have a project of a fuel injection system based on a 68hc11 that just
> starting to work fine. Could anyone help me with some info on the stepper
> motor used to regulate the idle speed of the engine. It's an G.M. IAC motor
> (I think). What I'd like to know is what voltage it works with (5V or 12V),
> what's the pin assignments, and if it is an unipolar or bipolar stepper
> motor.

You should consider scavanging an IAC driver chip from a GM ECM.  It is
a nine pine SIP and usually comes with it's own heat sink hat.  I've
seen it with two different part numbers - 23266 in older ECMs, and 34993
in the slightly newer ones.  It has four outputs (both ends of the two
IAC windings), a power (12V) input, a GND input, and three TTL control
inputs.  The control inputs are driven from a simple output port.  One
of them is an active high enable, while the other two specify the
winding polarities.  Stepping is software controlled from a 160 Hz
interrupt.

In a few days, I'll probably post the pinout of this chip on my web site
at http://www.cruzers.com/~ludis/ .

               unsigned long BinToBCD(unsigned long i) {unsigned long t;
Ludis Langens     return i ? (t = BinToBCD(i >> 1), (t << 1) + (i & 1) + 
ludis at cruzers.com            (t + 858993459 >> 2 & 572662306) * 3) : 0;}