Analogue-sequencer

Hi Robert,

> As far as I remember, I had this problem before I did the OS 
> upgrade: when I enter pattern edit mode I get a constantly 
> repeating message on the screen saying "Step 13 Velo 20", 
> as if the Velo pot of step 13 is constantly touched. The 
> update frequency is about 4Hz.
> 
> If I change the step 13 Velo pot to some other value, the 
> repeating message reflects the updated Velo message. 
> 
> Sometimes it gets triggered by some editing some other step, 
> but the last time I could leave pattern edit mode, enter it 
> and there it was again. 
> 
> It happens in stopped or play mode.
> 
> Looks like a hardware problem? Bad cable?

Not likely to be a bad cable - either a bad pot, or a bad multiplexer,
or possibly just a bad contact in the IC socket.
It hasn't been doing this since you got it, has it ?
Does the pot cover it's normal range of 1 to 127 if you move it from one
end to the other ?
By how much does the value change when it's constantly repeating ?

The pots are all fed with 5 volts, and each outputs a voltage between 0
and 5 volts depending on their position.
These voltages are selected in turn by the multplexers (4051 ICs), and
each voltage is fed to an 8 bit analogue to digital convertor.
The convertor has a range of 0 to 255, but this range is reduced to 0 to
127 by dropping the last bit before it's passed to the main code.
Also, the code that checks to see if the value has changed only acts if
the value has changed by 2 or more - this is so that if the pot is
positioned just on the boundary between one (8 bit) value and the next,
it won't flicker between them.
So for the pot to be seen as being constantly 'touched' takes quite a
bit of variation in the voltage.

The quick way to check whether it is the pot or the multiplexer causing
the problem would be to swap over the two multiplexer ICs on the upper
pot board. If that moves the problem to pot 5, it's the multiplexer. If
not, it's the pot.

Cheers,
Colin f