ECT and voltage divider help?

[Ludis Langens]

Daniel Houlton wrote:
> 
> After some math, I found the internal ECM resistor is
> around 1765 ohms, confirmed by both hot and cold readings.

What brand of ECM is this?  GM likes to switch between two different
pullup resistor values.  One for cold, one for hot.  Measuring the
voltage on the sensor won't work unless your trip point is far away from
the ECM's resistor switching temperature.

> Any ideas how I can do this?  I don't know a lot of the solid state
> devices.  Would I be using a transitor, op-amp, etc?

You need a voltage comparator.  A comparator is similar to an op-amp,
except the amplifier gain is non-linear.  The output is designed to
switch between on and off.  Generally speaking, a comparator will need
an external pullup resistor on the output because the output stage is
just an open collector transistor.

> Will tapping into the ECT wire to read voltage somehow screw up the
> reading to the ECM by acting as a sink or source?

Wire the ECT to the comparator through a high resistance - say 100K or
1M.  This will cause no problems.

> My question is, that he low-amp signal relay (needs to handle about 200
> mA max to trigger the fan relay coil) seems kinda big and bulky.  Is
> there a solid state device that can replace this?  Typically, a relay
> is used to drive a big load with a small signal, but I want to drive a
> small load with a small signal.  Just wondering if there was some kind
> of small IC that would do that instead of a big relay.

A transistor would work fine.  You can also get driver ICs that are
essentially a transistor and the circuitry to control it.

-- 
Ludis Langens                               ludis (at) cruzers (dot) com
Mac, Fiero, & engine controller goodies:  http://www.cruzers.com/~ludis/


----------------------------------------------------------------------------
To unsubscribe from diy_efi, send "unsubscribe diy_efi" (without the quotes)
in the body of a message (not the subject) to majordomo at lists.diy-efi.org