Circuit design help.

[ThePastRecedes]

I've got an idea of have in 8 pot's to control one parameter and with an stomp switch to cycle through the presets.
It would make more sense to do this digitally but I'd like to keep it simple.

The only way I can think of to do it is via a vactrol.

I found this schematic and I thought I could put a pot in place of the resistors to adjust the brightness of the led's thus the resistance in the other circuit. 


Do you have any other Ideas on how to do this?

thanks

[slacker]

Have a look at CD4051 chips, these let you route one input to one of 8 outputs, or the other way round. Depending on your circuit one or two of these would let you switch between 8 different pots.

Welcome aboard

[greaser_au]

this is an excellent idea, low part count - but the trimpots will take up a lot of room!

suggest you might:
step 1: figure out the useful limits of the adjustment of the vactrol LED current with a pot (careful with the minimum so you don't blow up the LED) and a diode (to account for the diode in the circuit) & find close resistors.
step 2: figure out if you need log or linear response and work out a spread of 9 intervals between them with 8 more resistor values.
step 3: Replace the LEDs in the circuit with 1N914/1N4148s. and replace the resistors with your 10 selected values.
step 4:  insert the vactrol  LED between the junction of the 10 resistors & ground...

I'd also start with a 0.47 uf capacitor across the switch to 'debounce' it

david

[merlinb]

An further option might be to use a 4-bit counter connected to a DAC (made from an opamp, say). Every time you press the switch it increments the counter, so you get a different voltage level from the DAC, and therefore a different current (brightness) through a single LED. Not sure if that would also work for you.

[ThePastRecedes]

Have a look at CD4051 chips, these let you route one input to one of 8 outputs, or the other way round. Depending on your circuit one or two of these would let you switch between 8 different pots.

Welcome aboard

Thanks for the welcome! I've been a member here for a while but just not posted since I could mainly find what I was looking for via the search funtions  But searching for this brought up to many irrelevant threads.

Just a side question, how to know about these different chips? Do you just gradually learn them through building various pedals? or other means?
I just been building Fuzz/overdrive/distortion pedals so this will be a new project for me, I don't know if it'll be feaseable yet.

this is an excellent idea, low part count - but the trimpots will take up a lot of room!

suggest you might:
step 1: figure out the useful limits of the adjustment of the vactrol LED current with a pot (careful with the minimum so you don't blow up the LED) and a diode (to account for the diode in the circuit) & find close resistors.
step 2: figure out if you need log or linear response and work out a spread of 9 intervals between them with 8 more resistor values.
step 3: Replace the LEDs in the circuit with 1N914/1N4148s. and replace the resistors with your 10 selected values.
step 4:  insert the vactrol  LED between the junction of the 10 resistors & ground...

I'd also start with a 0.47 uf capacitor across the switch to 'debounce' it

I was planning the pots to be 9mm alpha and the LED would be a lit when that pot is in function.

Thanks of the Idea of the denounce switch though, I'll try that out! I'm yet to have prototype my Idea yet I'm just gathering information on how to cycle between pre-set pot values

[ThePastRecedes]

Have a look at CD4051 chips

I'm about to do some googling around for theses.

Do you have any schematics about how to go about this bookmarked or saved any where. Don't worry if you don't google's my freiend 

[artifus]

http://www.beavisaudio.com/Projects/CMOS_Synthesizers/

more links at bottom of page

[ThePastRecedes]

What I'm basically looking for is to have the same function as a 8pdt rotary switch but controlled with a foot switch.

[artifus]

http://www.milkcrate.com.au/_other/sea-moss/#4051

4017 maybe easier than 4051 (not sure about the a, b,c inputs and a single switch - slacker?) here. a momentary switch from + to input would count through the outputs as in the schematic you posted. connect output 9 to reset for 8 button pushes.

this is far from perfect but may give you some ideas: http://www.diystompboxes.com/smfforum/index.php?topic=94909.0

*also* http://www.midiwall.com/gear/babyseq/ and http://www.nxp.com/documents/data_sheet/HEF4017B.pdf

[PRR]

> how to know about these different chips?

CMOS Cookbook, Don Lancaster, several re-prints and editions, take any readable copy. ABE lists six copies under $10 delivered. Worth much more.

The 4017 is a neat way to do it.

Your "next" switch won't work; or rather, it will work "too well". When a mechanical switch hits, it bounces several/many times. For a simple ON, you don't notice the stutter. But the swift CMOS counter will count every bounce. "One push" may give 7, 13, even 49 impulses, never the same twice. Lancaster has debounce circuits.

[ThePastRecedes]

http://www.beavisaudio.com/Projects/CMOS_Synthesizers/

more links at bottom of page

Beavis audio seems to be down 

[artifus]

it would seem so. dano will sort it out soon enough i expect. the milkcrate link above has some cmos info and check out the lunetta forum - http://electro-music.com/forum/forum-160.html for cmos stuff. also, google 'switch debounce' - that's what the last gate on the 4017 clock trigger schematic i linked to is intended to do.

*edit* http://www.nicolascollins.com/texts/originalhackingmanual.pdf