Sound card scope probe

[jsmcortina]

I find this such a useful and simple device that I felt the need to share it here. I'd urge all Megasquirt users to build one !
I use it with freely downloadable software "Audacity" from Sourceforge to record crank signals as a simple and highly portable alternative to a two channel scope.

Schem of scope probe

scope-probe.png (4.92 KiB) Viewed 4809 times

Assembled

100_1184.jpg (82.71 KiB) Viewed 4809 times

James

[a73camaro]

Since there can be up to 15 volts being measured on an automotive system, there should be a resistor divider attenuating the measured signal. I believe that sound card inputs are 200 millivolts peak. There are sound cards that have a capacitor on the input so DC or very low frequencies will not get measured.

I'm not trying to rain on your parade, just point out some limitations with the design.

[jsmcortina]

Did you notice the 1N4001 limiting diodes?

It is "cheap and nasty" but it works and I have found it extremely useful.

James

[adamsys]

Great timing! I just bought an external USB sound device to experiment with. Cheap ($25USD) and protects my laptop motherboard.

Did you notice the 1N4001 limiting diodes?

It is "cheap and nasty" but it works and I have found it extremely useful.

I did notice the diodes. They seem to be going in both direction, what is the theory behind that.

Here is a link to WinScope, software that uses the soundcard as a scope too. http://www.zen22142.zen.co.uk/Prac/winscope.htm"

They have info regarding the microphone and line-in voltages:

"The maximum input amplitude should never be higher than 10mV for a Mic input and 2Volt for the line input."

I assume the diode are a way to deal with this, no?

[a73camaro]

The diodes are voltage limiting. Once voltage gets above ~0.7 volts, the diode conducts and limits voltage. The diode in the opposite direction is for negative voltages. So yeah, I guess I noticed them.

[hassmaschine]

neat, I'll definitely have to build one of these. I probably already have all the parts..

[a73camaro]

Here is a circuit that attenuates the input signal


From here http://www.electronic-engineering.ch/radiocontrol/circuits/osziconn/connect.html

[jsmcortina]

As I said before, I've found the basic circuit I posted works for me. Try it.

James

[vlopsahl]

I made one after the first circuit posted. Tested it on my Audi A4 1,8T with a scope software I found on the net, Sound card scope 1.32 from Zeitnitz. First I tested the 60-2 trigger. I got this shot of the missing teeth. With this type of scope, is it so that I do not get any useful information about voltage? The scope software also makes an excel-sheet, and I calculated the idle to be around 900 rpm to check that it worked. I also tested the hall-signal on the cam.

Then I tested the idle control, integrated with the throttle body. It seams to be running at 500 Hz. This is a challenging thing to drive and I believe nobody has successfully made it work with standalone. I also think it is some kind of stepper drive, or dc-motor drive with a fine scaled TPS that sends feedback to the OEM ECU. Any thoughts on this?

Thanks
Vegard

[S.Bretz]

So this thing is hooked up to power and ground and turns slight voltage variances into an audio signal that can be looked at with some free software?

If so this would come in handy with the car and with the cars I work on at work.


Do both the left and right channels go to the same test point? and just ground the ground wire?

[jsmcortina]

Connect ground to ground
Left = signal 1 to be measured
Right = signal 2 to be measured (if required)

Low voltages only.

James

[ol boy]

Could this be used as a new software based VR conditioning circuit? Just an idea seeing the posted screen shots.
Thanks Ryan

[ol boy]

Okay here's what I got after building the above 2 channel scope.

20-1 wheel.

201wheel.jpg (165.18 KiB) Viewed 4465 times

One question.. or two.., okay three.. Where is my missing tooth in this picture? I have 41 tooth events on the picture shown but I don't see the missing tooth. Wheel is a 20-1. Should I have reversed the two leads on the VR sensor and see if that gave a slightly different log? Can I also log the 5 volt TTL for the LS2 coils, or is that voltage too high?

Thanks Ryan

[ol boy]

I downloaded one of the sound card scope software's listed above. Here is what I got. You can see the missing tooth good now. Did the math and got 750ish rpm. Pretty neat.

20-1 wheel.

20-1wheel2.jpg (130.77 KiB) Viewed 3651 times

[sfbmx88]

So based on the first diagram, what is the MAXIMUM voltage that you can safely test with this setup? No more than 5 volts?

[jsmcortina]

I've thrown more than 12V at mine, but the nature of the circuit means the input will be clipped. What voltage did you have in mind?

James

[dontz125]

The 1N4001s are rated for 50v. The load resistors are 1k, so 50V would give 50mA or 2.5W. If you're using little 1/4W resistors, they're the limiting factor - 15V through a 1k resistor is just under 1/4 W. While a VR circuit can push nearly 100V (IIRC), 1) it's AC, not DC, and 2) you aren't running this all day.

If you pop your 1/4W resistors, put in 1/2W!

[Rick Finsta]

James, I'm looking to use this to make composite logs with my MSI. I am running generic wheel with a dizzy, using a VR sensor and PIN36 with single coil control. Since PIN36 is a grounding signal, how can I hook this up so I can overlay both the VR and the IGN to see the relationship?

[Rick Finsta]

Anyone? Just looking to be able to test a ground signal on one channel and positive signal on the other channel for an overlay.

[jsmcortina]

Anyone? Just looking to be able to test a ground signal on one channel and positive signal on the other channel for an overlay.

Don't hook up to pin36 as the coil -ve connects there and puts hundreds of volts of back-EMF when the coil turns off. Instead scope at the low voltage signal
that feeds the BIP373. e.g. "top of R26" or wherever you have it connected.

James