Hey folks,

I'm very new to in-depth electronic theory, so I'm hoping someone could point me in the right direction... I'm working on a project car, and I need to take a PWM signal and use it to ground a relay. This signal outputs about 1v in the ON condition, 5v in the OFF condition. When ON, I need to somehow ground a relay. I don't know if there's an easy way to go about this.

Thanks.

 

What else do you know about this pwm signal, like what generates it?

 

What else do you know about this pwm signal, like what generates it?

It's the hvac control unit. It signals to the ECM to power the AC clutch on or off, at which point the ECM grounds the relay to turn on. I'm implementing a standalone ECM so need to find a way to mimic the old ECM

 

How did you measure that pwm signal?
A voltmeter or scope?

 

I don't have a scope yet. I was told by a fellow car owner.

 

Did the car owner mention how the voltage was measured? 1 volt RMS would have a higher peak-to-peak value.

Would it be correct to say that the signal will be either ground or pulses (same as PWM with a 0% duty cycle)?

Forgive me, but what is an ECM?
(Electronic Countermeasures in my book).

 

ECM=Electronic Control Module I would suspect same as an ECU, electronic control unit.
This circuit or a variation of might be all that is needed.
I would expect a signal similar as seen below.

 

Thank you for the waveform drawings as well as the other information as they clear up multiple questions. A picture is worth...

C1 is not critical. It just need to be large enough to make the ripple resulting from the PWM signal very small. With R1 being 47k and just guessing that the PWM is at least a few kHz, C1 can be pretty small, like 0.1 uf.

 

C1 is not critical.

Well I did some testing using that circuit and actually found a 10uf cap worked well from 500Hz to 150Khz pwm.

 

Wow, that's amazing... I couldn't make one of these myself. That visual depiction is awesome. Great community here; sorry I don't have more accurate information. I plan to purchase an oscilloscope and analyze the signal myself for clarity. I'll have to spend some time looking at this drawing. I'll find some reading material as well.

 

Do you feel confident in constructing the circuit?

 

Do you feel confident in constructing the circuit?

From the post sbove:

... I couldn't make one of these myself.

 

Not sure if the TS meant the circuit design or the actual construction is why I asked.

 

Interesting project. If the PWM signal is controlling an AC compressor clutch then it is a very slow signal, second not hertz. So the circuit in post #7 should work very well.