a little 555 4017 4066 resistor sequencer i drew up (unverified)

[Quackzed]

heres a pretty neat little add on circuit and isn't too bad as far as parts, other than the chips theres not much to it... switches between 3 resistors via a 555 oscillator...
it could be used to switch between diodes, or caps or even pedals with a few tweaks, its a bare bones thing but you can always add some transistors to drive leds for indication or add more steps by changing which pin you use to 'reset' the 4017...

a few caveats:
-----i did't figure the speed range, so r1 and vr1 will probably need to be changed 'my gut says r1 10k vr1 100k will be in the ballpark and have too fast and too slow available at the extremes, but why should i hog all the fun! 
-----also some kind of on/off switch would be nice, bypassing the sequencing as well as killing the osclillation maybee? more fun!
-----i'll guess it won't pop (i may be wrong) not sure about the internal switching of the 4066 as far as speed or transients but it might be fine w/out any pop resistor added... not sure.  are we having fun or what?!?
anyway feel free to use or refine or point out , it'd be great to get some feedback on it as far is shortcomings etc... to refine it into a neat little circuit add on for a broad range of uses.

[zurpman]

Quackzed,

Thank you for the schematic. I verified the circuit on breadboard just the other day, so its a good circuit here's some notes for anyone else that wants to use this.

with the values in the schematic the speed is so fast you cannot tell whats going on its crazy its like 50 pulses per second so I changed the 100k resistor to 470k and then I doubled the value of c 0.1u and now the var resistor i can get the pulse down to about 7  or so per second up to faster then i can count.

I did find that it introduced noise to the circuit in the form of a loud thump at the pulse rate. The noise is there even when idle and not playing. For now I'm testing a different solution to switching the resistors. I will turn this sequencer into a diode/Led sequencer at the clipping diode at a later time.

Thanks again man!

[Groovenut]

I did find that it introduced noise to the circuit in the form of a loud thump at the pulse rate. The noise is there even when idle and not playing.

You'll need to provide some serious supply rail decoupling between the 555 and the audio circuit. 555's tend to really crowbar the rail causing the thump.

[amptramp]

Unfortunately they discontinued this:

http://www.datasheets360.com/pdf/4019169642220112984

I used a dozen UA2240PC's to retrofit a Minshall Model E organ.  Since the output was mainly square wave, it sounded like a Thomas organ.  Nice flute and woodwind voicing, not that good for brass or string.   BTW the US ones worked well but the Korean ones didn't work - even if it is all on one IC, decoupling can be a pain.

[R.G.]

Change to a CMOS version of the 555 to get rid of the big thump, or at least to make it better, for the reason groovenut stated.

There are simpler ways to get the pulse oscillator, like a CMOS schmitt trigger gate, a resistor, and a cap.

[anotherjim]

I did find that it introduced noise to the circuit in the form of a loud thump at the pulse rate. The noise is there even when idle and not playing. For now I'm testing a different solution to switching the resistors. I will turn this sequencer into a diode/Led sequencer at the clipping diode at a later time.

Not just any resistor can be substituted in this way. You will get thumping if switching causes the DC level at either end to undergo step changes. Resistors that carry signal can be tricky.
The CMOS switches have a hidden gotcha. All in and out pins of the switches have reverse biased protection diodes between the pin and + (Vdd) and - (Vss) supply. To avoid those diodes conducting and clamping the signal by at least 0.5v, keep both ends of the controlled resistance at somewhere about Vdd/2 (half supply).

For clipping diodes, use the kind of circuit with an op-amp driving the clippers AND the clipper diodes return to Vref (half supply) rather than ground. That means there is no change in DC level when it switches, and the signal will not catch those protection diodes.

[Quackzed]

ok, here's a second attempt with version 2. this should (knock on wood) get rid of the thump.
As RG suggested, i used a schmidt trigger inverter oscillator instead of a 555, added some power filtering, and referenced the 4066's switches to 1/2 the supply voltage (v ref)<as anotherjim  recommended above> via some resistors and dc blocking caps...
the first version really was too bare bones, this one should work better and be thump free... i also added a resistor in series with the pot to keep the fastest setting available from being absurd, so making this resistor (*r1 )bigger is probably a good idea, it's 1k on the schem 10k might be a better value, youll have to try and see. this will slow down the max speed and as a side effect it'll give you a slightly slower slowest speed...

[anotherjim]

If board space is limited, an 8pin alternative for an easy oscillator is the LM567 . (also NE567, LMC567...)
Sadly, I can't find any suitable schematic to demonstrate it right now.
Other than that, I would go for the 40106 (or 4093) too.