analogue or digital? a PM3 hardware question

Maintenance, accessories, operation. Anything to do with making your erg work.
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sduane
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analogue or digital? a PM3 hardware question

Post by sduane » January 14th, 2007, 8:30 am

With apologies for this arcane post, and to anyone who's already seen it on the uk forum...

I've been using a scope to look at the signal from the flywheel pickup on my model D going into the PM3, and how it changes when connecting to the PC to run ErgMonitor.

I had been assuming the pulse waveform from the sensor is an analogue signal but, in trying to learn a bit of electronics I just read that smoothly varying signals can be turned into a "square wave", using a 555 timer chip. This might account for the sort-of-square pulses that I've seen, and how their amplitude varies with pace.

[or possibly a comparator chip rather than a timer?]

Does anyone know whether this sort of approach is used? I've no idea whether opening up the fan case might shed any light on this...

I'm not an electronics person, but hoped there might be an erg user out there who is, and who reads this forum, and who knows the answer :!:

If you've read this far and regretted it ... :oops:

Otherwise, I'm hoping the answer to this question will help me get ErgMonitor and the PM3 to work together reliably.

Thanks in anticipation...
Simon
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tomhz
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Post by tomhz » January 14th, 2007, 4:00 pm

Simon,

what exactly is your problem using Ergmonitor with the PM3+?

As far as I know the sensor sends a analoge signal but it is interpreted as a digital signal by Ergmonitor, i.e. Ergmonitor just measures the time for every 1/3 revolution with an accuracy of about 10 microsec

Tom
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haboustak
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Post by haboustak » January 14th, 2007, 4:08 pm

Simon,

The PM3 signal is definitely analog. I'm pretty sure it's a standard tachometer signal, if that helps you narrow down your reading/searching.

The PM3 measures the time between the square wave pulses and it calculates the fan's RPM. Each pulse occurs at a certain angle, so angular velocity is: (angle traveled) / (pulse time). From there the problem moves away from an electrical one to a mechanics/physics one.

PaulS will probably chime in soon with ErgMonitor-specific clarifications.

Mike
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johnlvs2run
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Re: analogue or digital? a PM3 hardware question

Post by johnlvs2run » January 14th, 2007, 5:37 pm

sduane wrote:I'm hoping the answer to this question will help me get ErgMonitor and the PM3 to work together reliably.
I think EM and the pm3 don't work at the same time with one sensor.

However if you hook up another cable pick up to the cage then both could be run at the same time in this fashion.
bikeerg 75 5'8" 155# - 18.5 - 51.9 - 568 - 1:52.7 - 8:03.8 - 20:13.1 - 14620 - 40:58.7 - 28855 - 1:23:48.0
rowerg 56-58 5'8.5" 143# - 1:39.6 - 3:35.6 - 7:24.0 - 18:57.4 - 22:49.9 - 7793 - 38:44.7 - 1:22:48.9 - 2:58:46.2
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Alissa
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Re: analogue or digital? a PM3 hardware question

Post by Alissa » January 14th, 2007, 6:02 pm

sduane wrote:Otherwise, I'm hoping the answer to this question will help me get ErgMonitor and the PM3 to work together reliably.
Hi Simon.

Why not just ask PaulS (who sells ErgMonitor) for help with whatever trouble you're having?

Alissa
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sduane
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Post by sduane » January 14th, 2007, 7:08 pm

Thanks for all the suggestions.

I've been in email contact with PaulS, who reports that splitting the signal to mic in (desktop pc) and PM3 works ok for at least some users, but is unsupported by him. Keen (I think) that the uncertainty might be resolved, Paul has already offered what information/help he can.

I have written up some recent thoughts and screenshots here http://www.duane-web.pwp.blueyonder.co.uk/scope.html
should anyone care to look.

The short story is that connecting to my pc and running EM modifies the shape of the pulse such that the PM3 can no longer reliably decide when a new stroke has been taken. The leading edge of the pulse gets rounded off quite a bit. (But not the trailiing edge.)

I suspect that it's a "feature" of my pc's on-board sound mic input.

Anyway, I'm reasonably sure I'll find a work around somehow, and promise to report the outcome here when I have sorted it out.

Cheers
Simon
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tomhz
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Post by tomhz » January 15th, 2007, 6:34 am

Simon,

there is an alternative. I added a 2nd sensor to my model C. I use the original sensor for the PM2 and the 2nd for Ergmonitor.

Tom
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sduane
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Post by sduane » January 15th, 2007, 7:49 pm

Tom

You're right, of course. When I sort out what's required for one sensor to drive both, I'll ask myself whether two sensors is the better solution, and may just do that.

Cheers
Simon
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c2scott
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Post by c2scott » January 18th, 2007, 6:33 pm

I suppose you could have a conversation with the electronics guy at Concept2, I don't think he has anything better to do... :?

You might be suffering from a ground loop issue: ground of the sound card vs ground of the USB cable vs ground of the tach vs ground of the PM3... you might try a 100uF electrolytic cap in line with the tach and ground signals before they go into the sound card; and make sure the wiring is right...
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