Troubleshooting an Arp Sequencer

[Brian Towles]

Jim Johnson wrote:

> I'm trying to repair an Arp sequencer using minimal tools - no scope - and
> I've run into something I can't understand.
>
> This problem has to do with the Step circuit. When everything is assembled,
> pressing the Step button causes the sequencer to advance, pretty
> consistently, by 11 or 12 steps. However, when the jack panel board
> containing the Step input jack is removed, it works correctly.

Could the switch be bouncing?  I don't know anything about the particular
setup, but that's what it sounds like to me.

Feeding the switch output directly into a digital input usually gives
multiple rising and falling edges as the switch makes contact.  If the
circuit is edge-triggered this is a major problem.  One solution is a
so-called "debouncer" circuit.  The circuit basically synchronizes the
switch's output with a slow clock ( 10-500Hz ):


  +5 -----    input      D Flip-Flop
           \  switch     |--------|
            -------------|D      Q|----------- debounced signal
                         |        |
  GND ----               |  Clk   |
                         |--------|
                             |
                             |
                       "slow" clock

There are other solutions to this same problem, maybe a LP fliter for
example.  Hope this helps.

Brian