[sdiy] Varying gate lengths (using a 4017 counter) for a simple sequencer?

[harrybissell]

"Roy J. Tellason" wrote:

> Way back in 1974 I bought a "color bar generator" to assist me in servicing
> color TV,  and it used that setup,  basically three trimpots which were (good
> thing!) accessible from the back of the unit,  forming part of a "frequency
> divider" chain that was analog!
>
> The thing was a real bear to keep in tune,  and I was always having to fiddle
> with it...

well of course :^P  Thats why digital counting methods replaced the analog way.
It
is doable, but you need to spend a lot of time assuring that the timing capacitor
is good...
the charging circuit is stable (and that includes temperature...) and that the
sync pulses
are good and stable.

My first drum machine... Popular Electronics "Thumpa-Thumpa Box" used this method
for
generating the drum division ratios.  It worked if you did a divide by 2, 3, 4
and not if you wanted
a divide by 8, 9 etc. The farther you went, the worse it got !!!

Since I worked for a company that used the same unijunction technology, I
replaced the 2N2646
with one of our premium industrial devices... and ended up with a drum machine
that could go
to about 300bpm.

Everytime a motor started in the house, the drum would skip a beat. Excellent
practice for a band...
it simulates the action of a real live drummer.  We nick-named it "stupid"

H^) harry