Swell pedal problem.

I originally acquired my console about 15 years ago. I had a lot of help from Ron Coates when I set it up - he converted the pedalboard to MIDI and also supplied me with a pair of swell pedals. However, I think he has now retired.

The swell pedals started playing up recently. First of all the left-hand pedal would go from closed to fully open after only about 20% of its travel, and I couldn't correct this in the HW settings. I decided in the end that the potentiometer was faulty, and managed to find an identical one online; it was quite cheap relative to the postage so I bought three to give me some spares. Replacing the potentiometer cured the problem and the left-hand pedal is now fine.

Then the right-hand pedal developed a different problem, which was that it seemed to be generating MIDI messages even when I wasn't using it. This was a problem when trying to use Autodetect to configure pistons etc. as quite often HW would detect the pedal instead of other controls. Curiously enough, it still functioned as a swell pedal, so I didn't immediately deal with it. However, I thought the problem was possibly also related to the potentiometer, so a couple of days ago I replaced that, too. The random MIDI messages seem to have stopped, but I couldn't get HW to detect the pedal at all.

I had heard that MIDI Ox can be useful in this situation, so I downloaded and installed it, and figured out how to get it to show what MIDI messages were being generated. With the left-hand pedal I see a series of hexadecimal numbers as I move it, counting up as I "open the box", and counting down as I "close" it. However, although the right-hand pedal generates MIDI messages when I move it, the numbers are all the same (they are all 7C).

My instinct tells me that the problem is probably not with the potentiometer but with the circuitry that uses its position to generate MIDI messages. The potentiometers in both pedals are connected to the same circuit board, which looks home-made - essentially it is a chip on a breadboard. The chip has PIC18F1220 printed on it, and as far as I can determine it is some kind of programmable micro-controller, so I suppose it has been programmed to scan the potentiometers for changes in resistance, and to use this to generate MIDI code.

I am not sure whether the circuitry has developed a fault; the fact that I have one working swell pedal suggest that it hasn't. Possibly it is reading the new potentiometer differently from the old one, but again I'm not sure why (I have checked all the connections, which I photographed before I started). Nevertheless, the most plausible explanation is that I have made an elementary mistake, the alternate one being that there is a limited fault in the hardware.

I'm not really sure where to go from here. Although I am quite technically-minded this is beyond my expertise. I also find it quite difficult these days rummaging around in the bowels of my console as I am generally very stiff from cancer in my bones and at 59 my eyesight isn't what it used to be. I suppose possibly I could get new MIDI circuitry and wire this up again to the potentiometers in the pedals, but I'm not sure what I would need for this.

Can you switch left and right (pedal potentiometer) connections to the encoder and see if the problem follows? Not impossible that the encoder has a problem.

Generally carbon pots have a life of approx 15K cycles (actuations). They aren't exactly the best performance wise for this application. They also get "noisy" as the deposited carbon wears off.

Rgds,
Ed

Check the new potentiometer that you soldered to make sure you didn’t bridge the solder, and that the wires aren’t touching any other terminals, and that the correct pins are soldered to the wires. Any of these can cause your problem. Also, many of the boards like yours have inputs for switches as well as for potentiometers. Make sure you didn’t wire it to a post for switches accidentally, and that it is properly wired to the board. Sometimes potentiometers are faulty. Check it with a multimeter to ensure it works, and that the pins do what you expect them to do.

Ed and Larason,

Those all seem like good suggestions, and they are straightforward, too.

I haven't touched the wiring on the board - there are long coloured wires coming from it which I have unsoldered from the old pot and soldered onto the new one. There don't seem to be any connections touching, but it is possible that I have missed something (varifocal glasses are useless for this sort of thing unless you are working at a desk) and indeed that I have soldered a dry joint. Going over everything with a multimeter sounds like the obvious next step, though it will involve a few contortions to get access.

If that doesn't identify the problem then I can swap the connections of the two pots to the board; this is a simple matter of swapping two soldered wires as they share the others.

If the new potentiometer is faulty, I do have another spare.

I will leave it until tomorrow as I have had a very frustrating day with a computer suddenly dying on me (not the HW one), and it took about six hours to get everything up and running again properly.

I followed your suggestions and went through the wiring carefully. Curiously, the problem turned out to be mechanical. The first time around I wasn't sure that how much travel it had compared to the mechanics of the pedal, so I started them both at one end to minimise the risk of accidentally pushing the pot further than it could go. However, I examined them both more carefully today and realised that the potentiometer describes a greater arc than the gearing on the pedal, and this time I centred them both, thereby avoiding the extremes on the pot. This seems to have solved the problem.

MIDI-Ox has revealed more strange behaviour, namely that my lowest manual is sending note-on and note-off messages in triplicate. I don't know why this is (possibly something to do with the way the three manuals are daisy-chained). However, on the principle of "it it works don't fix it" (which applies in medicine just as much as in engineering) I thought I should leave it well alone.

Thank-you both for your help.