Sound card scope probe

Ask questions about DIY board assembly issues, fault finding and testing. (Covers all Megasquirt versions and board.)

Moderators: jsmcortina, muythaibxr

Sound card scope probe

Postby jsmcortina » Sat Dec 04, 2010 11:47 am

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.

scope-probe.png
Schem of scope probe
scope-probe.png (4.92 KiB) Viewed 6722 times


100_1184.jpg
Assembled
100_1184.jpg (82.71 KiB) Viewed 6722 times


James
I can supply, repair or upgrade Megasquirts in UK.

My Success story: viewtopic.php?f=104&t=34277
MSEXTRA documentation at: http://www.msextra.com/doc/index.html
jsmcortina
Site Admin
 
Posts: 27928
Joined: Mon May 03, 2004 1:34 am
Location: Birmingham, UK

Re: Sound card scope probe

Postby a73camaro » Sat Dec 04, 2010 12:03 pm

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.
MSII v3.0, Extra 3.0.3s
User avatar
a73camaro
Experienced MS/Extra'er
 
Posts: 231
Joined: Fri Oct 08, 2004 6:44 am
Location: Dillon, CO

Re: Sound card scope probe

Postby jsmcortina » Sat Dec 04, 2010 12:08 pm

Did you notice the 1N4001 limiting diodes?

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

James
I can supply, repair or upgrade Megasquirts in UK.

My Success story: viewtopic.php?f=104&t=34277
MSEXTRA documentation at: http://www.msextra.com/doc/index.html
jsmcortina
Site Admin
 
Posts: 27928
Joined: Mon May 03, 2004 1:34 am
Location: Birmingham, UK

Re: Sound card scope probe

Postby adamsys » Sat Dec 04, 2010 12:28 pm

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?
adamsys
MS/Extra Newbie
 
Posts: 1
Joined: Sat Dec 04, 2010 12:12 pm

Re: Sound card scope probe

Postby a73camaro » Sat Dec 04, 2010 1:35 pm

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.
Last edited by a73camaro on Fri Dec 10, 2010 7:53 am, edited 1 time in total.
MSII v3.0, Extra 3.0.3s
User avatar
a73camaro
Experienced MS/Extra'er
 
Posts: 231
Joined: Fri Oct 08, 2004 6:44 am
Location: Dillon, CO

Re: Sound card scope probe

Postby hassmaschine » Sat Dec 04, 2010 2:57 pm

neat, I'll definitely have to build one of these. I probably already have all the parts..
hassmaschine
Super MS/Extra'er
 
Posts: 1331
Joined: Mon May 21, 2007 8:36 am

Re: Sound card scope probe

Postby a73camaro » Wed Dec 15, 2010 7:58 pm

Here is a circuit that attenuates the input signal
Image

From here http://www.electronic-engineering.ch/radiocontrol/circuits/osziconn/connect.html
MSII v3.0, Extra 3.0.3s
User avatar
a73camaro
Experienced MS/Extra'er
 
Posts: 231
Joined: Fri Oct 08, 2004 6:44 am
Location: Dillon, CO

Re: Sound card scope probe

Postby jsmcortina » Thu Dec 16, 2010 4:46 am

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

James
I can supply, repair or upgrade Megasquirts in UK.

My Success story: viewtopic.php?f=104&t=34277
MSEXTRA documentation at: http://www.msextra.com/doc/index.html
jsmcortina
Site Admin
 
Posts: 27928
Joined: Mon May 03, 2004 1:34 am
Location: Birmingham, UK

Re: Sound card scope probe

Postby vlopsahl » Mon Feb 28, 2011 1:23 pm

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
Audi 80Q 2,0 20V Turbo 630cc AEB/ABA/ABF
MS-II V3 MT2.25 MS2 Extra 2.0.1 VAG/Bosch VR 60-2 Waste spark PWM-idle
vlopsahl
Helpful MS/Extra'er
 
Posts: 136
Joined: Tue Jul 05, 2005 3:04 pm

Re: Sound card scope probe

Postby S.Bretz » Mon Feb 28, 2011 2:24 pm

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?
S.Bretz
Master MS/Extra'er
 
Posts: 521
Joined: Fri Nov 18, 2005 9:18 pm
Location: Lutz. Fl

Re: Sound card scope probe

Postby jsmcortina » Mon Feb 28, 2011 4:26 pm

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

Low voltages only.

James
I can supply, repair or upgrade Megasquirts in UK.

My Success story: viewtopic.php?f=104&t=34277
MSEXTRA documentation at: http://www.msextra.com/doc/index.html
jsmcortina
Site Admin
 
Posts: 27928
Joined: Mon May 03, 2004 1:34 am
Location: Birmingham, UK

Re: Sound card scope probe

Postby ol boy » Mon Feb 28, 2011 9:15 pm

Could this be used as a new software based VR conditioning circuit? Just an idea seeing the posted screen shots.
Thanks Ryan
289 SBFord, Torquer II EFI intake, 36lbs injectors, 8 LS2 coils in waste spark and a TURBO!, 4R70W, MS2extra 3.4a6
ol boy
Master MS/Extra'er
 
Posts: 723
Joined: Mon Sep 10, 2007 3:06 am
Location: Tucson, Az

Re: Sound card scope probe

Postby ol boy » Sun Mar 06, 2011 10:26 pm

Okay here's what I got after building the above 2 channel scope.
201wheel.jpg


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
289 SBFord, Torquer II EFI intake, 36lbs injectors, 8 LS2 coils in waste spark and a TURBO!, 4R70W, MS2extra 3.4a6
ol boy
Master MS/Extra'er
 
Posts: 723
Joined: Mon Sep 10, 2007 3:06 am
Location: Tucson, Az

Re: Sound card scope probe

Postby ol boy » Mon Oct 03, 2011 6:57 pm

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.

20-1wheel2.jpg
289 SBFord, Torquer II EFI intake, 36lbs injectors, 8 LS2 coils in waste spark and a TURBO!, 4R70W, MS2extra 3.4a6
ol boy
Master MS/Extra'er
 
Posts: 723
Joined: Mon Sep 10, 2007 3:06 am
Location: Tucson, Az

Re: Sound card scope probe

Postby sfbmx88 » Fri Oct 21, 2011 4:37 pm

So based on the first diagram, what is the MAXIMUM voltage that you can safely test with this setup? No more than 5 volts?
sfbmx88
MS/Extra Newbie
 
Posts: 1
Joined: Fri Oct 21, 2011 3:24 pm

Re: Sound card scope probe

Postby jsmcortina » Sat Oct 22, 2011 3:35 am

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
I can supply, repair or upgrade Megasquirts in UK.

My Success story: viewtopic.php?f=104&t=34277
MSEXTRA documentation at: http://www.msextra.com/doc/index.html
jsmcortina
Site Admin
 
Posts: 27928
Joined: Mon May 03, 2004 1:34 am
Location: Birmingham, UK

Re: Sound card scope probe

Postby dontz125 » Sat Oct 22, 2011 2:26 pm

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! :lol:
dontz125
Super MS/Extra'er
 
Posts: 1948
Joined: Mon May 11, 2009 7:14 pm
Location: Scarborough, ON

Re: Sound card scope probe

Postby Rick Finsta » Mon Nov 21, 2011 9:52 am

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
Experienced MS/Extra'er
 
Posts: 278
Joined: Fri Dec 10, 2010 4:41 pm

Re: Sound card scope probe

Postby Rick Finsta » Sun Dec 11, 2011 12:06 pm

Anyone? Just looking to be able to test a ground signal on one channel and positive signal on the other channel for an overlay.
Rick Finsta
Experienced MS/Extra'er
 
Posts: 278
Joined: Fri Dec 10, 2010 4:41 pm

Re: Sound card scope probe

Postby jsmcortina » Sun Dec 11, 2011 12:24 pm

Rick Finsta wrote: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
I can supply, repair or upgrade Megasquirts in UK.

My Success story: viewtopic.php?f=104&t=34277
MSEXTRA documentation at: http://www.msextra.com/doc/index.html
jsmcortina
Site Admin
 
Posts: 27928
Joined: Mon May 03, 2004 1:34 am
Location: Birmingham, UK

Next

Return to Board assembly and testing

Who is online

Users browsing this forum: No registered users and 1 guest