Analogue-sequencer

On Thursday 15 January 2004 20:02, Colin f wrote:
> 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 ? 

Not that I remember. I'm now sure I had this problem a 
couple of days ago, and maybe earlier.


> Does the pot cover it's normal range of 1 to 127 if
> you move it from one end to the other ?

I studied it some more and it looks like I can stop the 
messages van I move the velo value in the range > 105 or 
so. 

It also looks like *two* similar messages are intermixed. 
Like two pots are reporting changes. If I turn down the 
step #13 velo pot to value 1, I can clear see that a 
message with value 9x (ninetysomething) is mixed with the 
message reporting the 1 value. That other message also 
seems to have an other step number.

> By how much does the value change when it's constantly
> repeating ?

As said above, it is alternating with a message from another 
step with its own value. Don't know yet which step it is.


>
> 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.

I'll give that a try, tomorrow, if Boele is OK with it.

- Robert