[sdiy] TB303 debounce?

Richie Burnett rburnett at richieburnett.co.uk
Fri Feb 10 12:56:34 CET 2012

The tact switches in the 303 are read periodically by the microcontroller. 
(1.8ms interrupt)  So there is probably already some switch debouncing going on
in the software.  However, this can only do so much.  (The exception to this is
the Run/Stop switch which is debounced using conventional hardware, which you
could tinker about with!)

I've replaced tact switches on several TB-303 machines and investigated a few of
the worst components after removal.  They really were in a terrible state
electrically.  You had to push down quite hard to get a good low resistance
electrical contact, and even then any side-to-side movement of the finger would
cause rapid-fire breaking and making of the contact.  No software is going to be
able to filter out bounces that happen hundreds or even thousands of
milliseconds after the initial key down.

If in doubt whip the switches out.  Replacement is an easy enough job to do,
just handle those old phenolic PCBs carefully as they are prone to hairline


> Hi all,
> Has anyone ever looked at the TB303 circuit to see if some quick
> switch debounce could be added so we don't have to replace all these
> marginal switches?
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