5V signal for resistive short testing?

Watched the ATS video posted by Bernie Thompson on diag.net yesterday:

diag.net/msg/m7a7t76n7owc590sss1x9j17so

I can't link to the video directly. Sorry. But the relevant part was where he used a 5V signal generator to find a problem in PCM that was causing the O2 bias voltage to get partially pulled to ground. It was a really slick test.

And that got me thinking. Would a home made 5V signal generator accomplish the same thing? I don't think it'd have to be a square wave, just a low current that's sensitive enough to get pulled down by a resistive short. Less than 50mA, maybe.

Would the Power Probe 5V adapter work? I have no idea what kind of current those output. :silly:

I will have a good look at it tomorrow --- thinking most labscopes have a 5v square wave signal generator.

Tyler wrote: And that got me thinking. Would a home made 5V signal generator accomplish the same thing? I don't think it'd have to be a square wave, just a low current that's sensitive enough to get pulled down by a resistive short. Less than 50mA, maybe.

This is a signal generator that I built for bypassing VATS/Passkey. Pulling the signal down with a test-light to ground (27Ω). There was a considerable voltage drop, pulling 11.6 mA.



I added various amounts of resistance and the voltage drop and current flow changed accordingly. Adding 44K Ω resistance to the test-light, still, had a voltage drop of .45 volt, pulling only .05 mA.

Found this on amazon for $12 and change. Adjustable frequency and duty cycle so it might also be useful for driving PWM controlled outputs. Should be able to current limit it with a resistor like Chad mentioned in his post.

OK I guess right click doesn't work for anything on this site once you register?? Searching for B07KVYQ78K on amazon should bring it up.

You guys are awesome. This is exactly the kind of stuff I was looking for.

I was initially thinking about making this 9V to 5V regulator? Mostly because I have all of those components at work (except the optional LEDs):

somanytech.com/9v-to-5v-converter-circuit/



But these suggestions are way better. :lol: I wonder how hard it'd be to combine one of these regulators with a voltmeter across the output? That way, I wouldn't need to tie up my scope/meter measuring for a voltage drop. It'd all be in one piece of equipment.

Matt T wrote: OK I guess right click doesn't work for anything on this site once you register?? Searching for B07KVYQ78K on amazon should bring it up.

Yeah, that's a new security function we added a couple months ago. Sorry for the hassle. Here's the link for anyone following along:

www.amazon.com/Generator-DROK-Adjustable...ngular/dp/B07KVYQ78K

Another option I considered was the Ditex AutoSim Pro:

www.aeswave.com/AutoSim-Pro-Automotive-S...Simulator-p9749.html

It'll do a bunch of cool stuff! But it's also $400. More money than I wanted to spend...

That Ditex does look nice. For something more advanced than PWM, but cheaper than Ditex, amazon B0759GKKBJ or similar might work as a sensor simulator.

Ended up ordering the DROK signal generator from Amazon, because it's fast and I'm cheap. :blush:



I rigged it up with some spare wire and clips I had on hand for some quick tests. Two wires in for power/ground, one power switched output equal to input voltage, and one steady ground. Because the signal generator is connected to the vehicle battery for my tests, I generally found the steady ground wire to be useless.

You can play with the duty/frequency, but I generally found myself turning the duty all the way up to generate a flat 12V. With a dead short and a battery at 12.06V, the generator flows 12mA of current:



So what kind of a short does it take to pull that down? I started playing with a 10K ohm variable resistor to see how the voltage would behave:



Cursor #1 is an open circuit, 12V. Cursor #2 shows the resistor connected at 10K ohms. It's clear that even 10K ohms is enough to pull this generator down.

For giggles, I dialed the voltage in to 5.01V, then checked the resistance reading. 700 ohms on the nose.

For more giggles, I also tried to run one of my Nissan three-wire ignition coils off the signal generator. Didn't work. Signal was making it all the way to the coil, but apparently 12mA isn't enough? Voltage applied by the generator was 1.07V while connected to the coil. Oh well...