question about expression pedal

[tomcody]

    Hi everybody ;D I want to use an expression pedal in MB64 but there are a problem with these things, the pedal in fact don't turn over the whole range the pot inside them: for example if his pot's value is 10kOhm, the pedal's output resistance range is not between 0-10k, is between 3k <--> 7k.

My question is: How I do configure MB64 to send (for example) value 0 at 3k, and value 127 at 7k, instead of 0-10k?  ??? ???.

    Thanks you all for your time and any help!!

[stryd_one]

Sounds like your pedal doesnt have the right kind of pot in it....

Look for TK's value-scaling algorithm :)

[/tilted/]

The range you mention is a little less than half of the total for your pot. This should be ok anyway, since the AD converters in these PICs are 10 bit (I think) and you only need 7 bit for a MIDI CC...

I think you could get better range/jitter figures if you increased the supply to the top end of your pot, to say 6 or 7 volts. The best would be to adjust it so that your "at full" voltage is as close to 5v as you can get, without going over.

All that said, there's probably some analogue trickery you could do with opamp/comparators to achieve scaling in the analogue world (ie before you get to the PIC), so if you needed a 14 bit controller, you'd still get reasonable resolution from it.

Unfortunately I'm way too tired/busy to figure out analogue scaling functions...