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there is no limitation of pulses / rev

did you scale R4 / C3 according to the wiki article?
https://code.google.com/p/multidisplay/wiki/RPM
No, I didn't. I missed that part... I used R4=130kOhm and C3=47nF according to https://code.google.com/p/multidisplay/wiki/PartListV2.

According to the datasheet the output voltage of the frequency converter reaches maximum when the pulse frequency reaches f = 1/(R4*C3), which is 164 Hz. I have 2 pulses/rev ==> 164Hz = 4920 rpm.

In real life I don't reach 4920 rpm either, my rpm numbers won't go beyond 3450 rpm, which should correspond to about 3.5 V output from the frequency converter.

Maybe I should test changing the R4 to something with a lower resistance, e.g. the 60 kOhm resistor I just found among the leftovers. With R4=60kOhm 5V output from the frequency converter should correspond to 10600 rpm for my 2 pulses/rev. And if I'm still limited to 3.5 V output it would still cover rpms up to 7460 rpm.
Now R4 is changed from 130kOhm to 60.4kOhm on MD03 and now the RPM signal works over the full range. However, the rpm signal seems non-linear. I'm reading correct values up to 3000rpm, then the rpm values on the MD goes a little bit high, at 4300 it shows 4500 rpm and at 5300 it shows 5800 rpm. At 5300 rpm the deviation is 9% then.

But I'll look into that later. Maybe I'll just add a line in the code to make the rpm a 2nd degree polynomial instead of a 1st degree. This seems to me to be the easiest way around it...
By the way, I think it would be good if you point out in the partlist that you need to adjust C3 & R4 to your RPM setup. I know that it is mentioned in the general MD03 buildup page but I missed so I guess there are more people missing it.

On the https://code.google.com/p/multidisplay/wiki/PartListV2 it says in the MD03 RPM section:
| 1x | R4 130k | ...
...
| 1x | C3 47nF | ...


Instead you could have:
| 1x | R4 130k (value depending on your RPM setup) | ...
...
| 1x | C3 47nF (value depending on your RPM setup) | ...
, where "RPM setup" is a link to the RPM measurement wiki page.
done; its in the partlist now!
15 posts Page 2 of 2

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