Re: Fuel pump relay....RPM limits

[steveb@newkla.kla.com (Steven Buchholz)]

> For those of you that wanted a reversed engineered Audi fuel pump relay,
> RPM limit circuit, here some of it. Does anyone know what the MC14538 is?

It's a dual retriggerable/resettable monostable multivibrator.  

>>>> cool ASCII diagram deleted <<<<
> 
> The ignition pulse seem to come in on pin 10. Pin 4 goes to the relay coil.
> Pins 1, 8, 12, 15, and 16 are connected to a common ground.
> Pins 6 and 9 are not connected to anything.
> 
> It appears to be a timing circuit. Probably changing the 120K or the 37K
> resistors (or the caps) would affect the RPM limit.

I think you're right about the purpose.  I think that there may be a slight
error in your circuit diagram though.  The 120K/0.1uF common point is conn-
ected to pin 2, which is correct for the first stage, but the common point
for the other MVB is pin 14, which would imply that there should be a cap 
to ground connected to the 100K resistor you show.  Pins 1,8 & 15 should
be connected to ground, but pin 16 should be connected to +12.  Could you
have the input & output reversed?  Pin 10 is an output and pin 4 an input.
I can believe that pins 6 & 9 would have no connection.  Could the common
connection of the 100K & 120K resistors as well as pins 3 & 5 actually be
at +12v as well?  If the diagram is correct, the output of the first stage
(pin 7) is RC coupled to the Reset pin on the second stage through the 
37K and 1uF cap ... this also seems a bit strange.  
> 
> If anyone has any info on the IC, let me know.

I've got the spec sheet right in front of me ... let me know if you want 
a copy ... include fax number if you want me to send it by fax.

Steve Buchholz
s_buchho@kla.com
San Jose, CA (USA)