Good question.  PWM (Pulse Width Modulation) is a way of controlling
electrical power digitally.  Let's say you want the idle air valve
partially open.  It's actually kinda hard (re: expensive) to limit the
current flow to the valve.  So instead, we just switch it on-off-on-off...
very quickly.  Since it's only switched on part of the time, the amount of
current reaching the valve is limited, and if we do it quickly enough, the
valve acts like it's getting a controlled amount of constant current fed to
it.  Typically in PWM applications the frequency of the pulses remains
constant and the width, or length of time the voltage is on is varied.  So,
for example, suppose one on-off cycle is 10 milliseconds.  If we want to
limit our output to 50%, the voltage is switched on for 5 msec and off for
5 msec, and repeated over and over.  if we want 80% power, we switch
voltage on for 8 msec and off for 2 msec.  This allows us to digitally
control an analog output very easily.

On Sat, Nov 16, 2013 at 8:13 AM, JRodgers <jrodgers113@gmail.com> wrote:

> Uh, I seemed to have missed something in this discussion What is a/the
> PWM? It just doesn't come to me.
>
> Thanks,
>
> John
>
>
> On 11/15/2013 10:03 PM, Brett Ne wrote:
>
>> GoWesty emailed back and declined to share their information, citing "that
>> data is proprietary".  It really isn't, just as knowing the expected
>> output
>> voltage range of a healthy voltage regulator isn't proprietary.  Oh, well,
>> it was worth a try...it just means a little more work on our part.
>>
>>
>> So, here's what we need to know:
>> * The PWM duty cycle being feed to the idle air valve when:
>>       --the engine is cold, the starter is engaged, and the coil is
>> shorted
>>       --the engine is cold & running
>>       --the engine is fully warm & running
>>       --the engine is fully warm & running with PS operating
>>       --the engine is fully warm & running with AC on
>>       --the engine is fully warm & running with PS operating and AC on
>> *  The current draw from the idle air valve at a known duty cycle.(or feed
>> it straight 12v and measure the current draw.)
>> * The base voltage and the peak voltage coming from the Hall sensor
>> The above items will need to be done by someone with a scope and a healthy
>> ICU & idle air valve(and PS & AC).
>>
>> *  Which connector, 4/ST2 or 11/ST1, supplies the PWM power to the idle
>> air
>> valve. (and confirm that whichever supplies the PWM power, that the other
>> is a ground connection.)
>> *  What is the voltage at the coolant temperature sensor when cold and
>> when
>> 160 F.
>>
>> I think that this would provide all the information needed to design the
>> circuitry and program the microcontroller to drive the idle air valve.
>>
>>
>>
>> And once a prototype is built, we will need a vict-- I mean volunteer-- to
>> connect it to their rig for testing & fine tuning.  Preferably in the
>> Portland, OR area.
>>
>>
>> --
>> Brett in Portland, OR
>> "Albert" '82 VanFox I4 Riviera
>> .
>>
>>

--
Brett in Portland, OR
"Albert" '82 VanaFox I4 Riviera