Sound card scope probe

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

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Sam280Z
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Re: Sound card scope probe

Post by Sam280Z »

I've made the scope probe as described in this post. I've been playing with it using this software which includes a signal generator: http://www.zeitnitz.de/Christian/scope_en. I fed the generated signals back to the mic through the headphone jack. All in all, it works pretty darn good.

I did come across one major stumbling block:vBy default, widows (particularly laptop installs) has some signal processing on the mic input. The result (for me) is both channels showing the same or similar signal. This is easily turned off, but it took me three laptops and a bit of frustration to figure it out.

Thanks,
Sam
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meeki007
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Re: Sound card scope probe

Post by meeki007 »

You can build a USB scope for 10 bucks that works too and does not risk your sound card.

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Sam280Z
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Re: Sound card scope probe

Post by Sam280Z »

Just to be clear, I didn't damage the laptops or their soundcards. I was just trying different laptops because of the weird behavior.
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JAM
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Re: Sound card scope probe

Post by JAM »

I have constructed my sound card scope probe and it works good on the left channel, in fact in stereo mode it outputs the left signal onto both the left & right channel output graphs on the screen but nothing on the right. I would like to overlay the signals, does anybody know if this is a setting in audacity that is causing the same signal to output on both graphs in the software? I could not figure it out :?:
Rick Finsta
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Re: Sound card scope probe

Post by Rick Finsta »

Bump for a question on this. It worked great for plotting my VR sensor inputs and figuring out R52/R56 and phasing on that, so first and foremost thanks for an invaluable tool! Now, I want to use this to set my PWM parameters for my low-Z injectors and also to check dwell as I bring ignition control online. As such, I removed my TIP120 setup on FIdle and reinstalled the "stock" components for that ouput, and reinstalled R37, R38, and R43 after reading these are needed for scoping these outputs (and that the current-limiters are recommended for low-Z injectors - missed that during assembly it seems).

Running on the JimStim I can't seem to get any signal from the injectors in test mode and I'm not sure if I'm connecting the leads properly. I read this thread and connected my leads as described by "robs" in that thread, and got no signal, so I tried grounding on the JimStim and on the v3.0 Main Board with the same results; nothing but 60-90Hz noise. Do these need to be connected to injectors to get signal here? Is there another point in these circuits I can attach my leads to check and see if the circuit is outputting proper values?

I'm electrically illiterate so I tried looking through the schematics but just ended up going cross-eyed after a while.
Michael
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Re: Sound card scope probe

Post by Michael »

What a brilliant idea! I have 'scopes, but with this for basic checks, especially on the road, I can have everything on the laptop and leave the 'scope at home. Great!
Manu
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Re: Sound card scope probe

Post by Manu »

Hi,

there is another solution, less cost effective :-(
I have one Hantek 1008C wich is a 8 channels oscilloscope :
http://www.hantek.com/en/ProductDetail_136.html

You can find it around 90$ shipping included on ebay. Cheap, reliable and easy to move.

Best regards,
Manu
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Rick Finsta
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Re: Sound card scope probe

Post by Rick Finsta »

Anyone? Where can I get a positive voltage signal from the injector driver circuits for an MS2 on a v3.0 mainboard?

ETA: Okay I *think* I can test Pin 1 of Q1 (INJ-1) or Q5 (INJ-2) with the scope grounded or I can test across R15 (INJ-1) or R20 (INJ-2) or Pins 7 and 5 to ground on U4?
Matt Cramer
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Re: Sound card scope probe

Post by Matt Cramer »

Rick Finsta wrote:Anyone? Where can I get a positive voltage signal from the injector driver circuits for an MS2 on a v3.0 mainboard?

ETA: Okay I *think* I can test Pin 1 of Q1 (INJ-1) or Q5 (INJ-2) with the scope grounded or I can test across R15 (INJ-1) or R20 (INJ-2) or Pins 7 and 5 to ground on U4?
Is this what you're looking for?

http://www.diyautotune.com/tech_article ... ooting.htm
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Rick Finsta
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Re: Sound card scope probe

Post by Rick Finsta »

That's the article I read that gave me the pin ideas I posted above. I didn't hear an emphatic "no" so I'll assume I am good to go connecting the scope to the place I mentioned to get the PWM waveform and later on to test injector dead time in the car? Thanks!
Matt Cramer
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Re: Sound card scope probe

Post by Matt Cramer »

I'm not sure a scope would be particularly useful for measuring dead time.
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Rick Finsta
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Re: Sound card scope probe

Post by Rick Finsta »

Perhaps I mean opening time? In the thread I linked above it was being used to tune injector characteristics...

Is dead time the measure of when the injector is actually spraying fuel whereas opening time is the time where full voltage is needed to snap the valve open before PWM kicks in to hold it there?
Rick Finsta
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Re: Sound card scope probe

Post by Rick Finsta »

Putting the scope across R15 and R20 gives me great signal; I can see the initial voltage and then the PWM kicking in, and it lines up with the exact PW I am setting in the test mode! I am using THIS software for checking voltage, pulse width, and frequency, and then I am using Audacity to record.
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Re: Sound card scope probe

Post by jsmcortina »

Rick Finsta wrote:Is dead time the measure of when the injector is actually spraying fuel whereas opening time is the time where full voltage is needed to snap the valve open before PWM kicks in to hold it there?
This was discussed a number of years ago - but I believe it to be invalid. Another false "method" was to find the PW at which the injector just dribbles fuel - no good.

Flow test the injector to know what is going on mechanically. Plot the graph to find the real dead time.

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Matt Cramer
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Re: Sound card scope probe

Post by Matt Cramer »

The number you describe would be the PWM time threshold. Useful for setting up PWM current limiting, but it's not the same as dead time.
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Rick Finsta
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Re: Sound card scope probe

Post by Rick Finsta »

Sounds like injector flow methods are similar to .050" versus seat-to-seat cam timing numbers...

So long as I can see the voltages and PWs line up as they should I at least have the warm fuzzies.
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