Concept 2 Analog in instead of flywheel input?

[PumaFPV]

Hey, first of all amazing work and documentation for this project!

I have an old Concept2 PM2 that I would like to convert with this project. I'm not sure if I want to open the flywheel to add magnets and a hall effect sensor, I'd rather use the existing output, but I guess it would require reading from the ADC, and maybe require an amplifier...
Have you considered adding support for such a thing? (I havent checked the code yet to see if I would be able to add support myself)

Cheers

[PumaFPV]

By looking at previous issues, I discovered the discussions tab in github... I've never seen it being used before. So maybe I should have posted there...

[Abasz]

Thanks. I moved it to discussions.

Indeed for the PM2 pickup to work you will need an amplifier. But even in that case the on board ADC will not work. Detecting the signal requires a digital input because it uses interrupts. ADC-s are polling which means that need to check for status of the pin every time which requires a hell of a lot of resources. So this is not the right way.

What you can do is that after amplification, you can feed the analogue signal into a binary digital converter circuit with e.g. a voltage comparator where the trigger voltage is set by resistance (IC e.g. the LM393). But this is not the most simplest circuit but probably you can get a ready made board (module) with adjustable resistance module, just select one that supports voltage range you amplify to. This will yield consistent switching which is important.

Other option is a mosfet with a low gate source voltage (e.g. BS170) could work, the important part is that it is a consistent switch, but this would need to be tested. Here when the analogue voltage exceeds the VGS the transistor switches on and gives a signal. But this is tricky as Vgs is always minimum typical and maximum so needs testing.

My personal view is that hall sensor is the way to go. It is very simple you just replace the current pickup with a hall sensor and wires. I think magnets are already inside (3 to be precise) so you just swap out the pickup.

Here is a discussion on this topic (though its more about settings then actual hardware but you can as the user how he fitted the hall sensor): JaapvanEkris/openrowingmonitor#49

[PumaFPV]

ohhh ok thanks for the explanation!
I wonder how they do it then. Maybe I'll do a bit of reverse engineering on the PM2. There is an IC call C2PM2V63. Which sounds a lot like Concept 2 PM2 (so some sort of custom IC...) (But that's on the lower part of it, which I guess is the digital part). At the top lies the analog part, containing op-amp and comparator. I'll get my scope and probe around :)
I didnt check how the "complex name" algorithm works, but I though the peaks heights could have helped the estimation. But if only the delay between each peaks matters than indeed a digital signal is the way to go.
But I guess in the mean time I'll order some hall effect sensors!
Thanks again for the work and the time you took to explain :)
Nicolas

[Abasz]

PM2 doest the following (source: https://www.c2forum.com/viewtopic.php?t=94893)

• There is a coil of wire that has a fixed resistance.
• When magnet passes the resistance changes (sinoid-ish curve) hence the voltage changes (in milli volts range)
• They feed it into the amplifier so they have some decent voltage
• Then use the voltage comparator to trigger high and low

Actually trying to piggy back the current PM5 circuit (amplifier and comparator) is a good idea. You just try to find the signal from the comparator.

We need digital signal because the algorithm measures the time between impulses and than that is used to calculate the speed of the flywheel (velocity to be precise) and from that all the other metrics in line with the "Physics of Ergometers"

Changing to hall is extremly easy (though I dont have concept 2 to be fair :)

you can get a borad like this:
https://www.joy-it.net/en/products/SEN-KY003HMS

You take the the current pickup out (there are schismatics on concept 2 web site, but it is near the shaft of the flywheel, but I think there is no need to take the flywheel off but rather the black cover)

Then you fix the board and bend the hall so it is close to the passing magnets. That is it.

[JaapvanEkris]

Just for completeness: there is a standard PCB design for a Raspberry Pi that might be easily modified for a ESP32: laberning/openrowingmonitor#157