General => Open Discussion => Topic started by: AllenM on May 07, 2019, 02:06:46 PM

Title: Custom "Volume" Pedal
Post by: AllenM on May 07, 2019, 02:06:46 PM
Guys.. need some help.

Received a request from a local player to create a custom volume pedal. His idea is to have a pedal with two or three foot switches that would allow him to adijust the volume Up, Down and possibly bypass. He later added maybe having leds that showed the current output level. So after talking to him what it looks like he wants is a pedal that will allow him to step the volume down at set increments (with 10 to 16 steps) and then step the volume back up to unity.

What I think I would need is an IC that would allow we to step up/down thru several resistor values to emulate turning a pot up / down. Not looking to boost the signal. From there I would imagine a second IC of the same type to control LEDs representing the current "level". Then wire up a standard bypass.

Any help would appreciated if anyone knows of a sample circuit or IC that would help get me started. I just started searching thru google, but figured someone here may already have an idea of where to start.

Title: Re: Custom "Volume" Pedal
Post by: alanp on May 08, 2019, 12:24:42 AM
Easiest way I can think of is an opamp with a vactrol controlling the gain on the resistor side, with the LED side of the vactrol being controlled by some kind of microcontroller's DAC output (or PWM or something, for variable brightness.)
Title: Re: Custom "Volume" Pedal
Post by: mjg on May 08, 2019, 03:35:04 AM
There's this approach, which is a micro controller, DAC and ADC, and write the software to control the volume (or other DSP).  It's probably overkill for what you want:

I quite like Alan's suggestion! 

The fun part will be that he wants 'set increments'.  Matching up the brightness of an LED to 10 equal steps in terms of volume might be tricky?  You might need to have a log scale or something to make it sound right?
Title: Re: Custom "Volume" Pedal
Post by: mjg on May 08, 2019, 03:41:54 AM
Also, I think you'd probably only need the one micro controller to control the volume, and the LED display. 

Check out something like this as an example - it has LEDs, but also a driver so you can control them all using just 2 pins from your micro controller:

Title: Re: Custom "Volume" Pedal
Post by: mjg on May 08, 2019, 03:45:35 AM

What about just using a digital potentiometer, and wire it up like you would a volume pot?

e.g. this one is 100k, has 128 pre-set positions, and control from a micro controller:
Title: Re: Custom "Volume" Pedal
Post by: Aristatertotle on May 08, 2019, 07:26:58 AM
Maybe do something like what Alan said, but use the LM3916 as the led driver?

Basically opamp set up with vactrol to control gain and the LM3916 controlling the led in the vactrol. To control the LM3916, have the pot on the volume pedal set up as a voltage divider tied to a power source and the control pin of the LM3916. Then you could have a bypass switch for the pot to bring it to max gain?

Makes sense in my mind, don't know if it makes sense here. I'll draw up a basic diagram for what I mean later.

All that said, something like an Arduino is the route I'd go.
Title: Re: Custom "Volume" Pedal
Post by: HamSandwich on May 10, 2019, 02:05:01 PM
Check out the ZVex seek trem. Instead of pots, use set resistors. I think it even has LED's already? Rather than scrolling through with a rate, you'd have to click through. Where there's a will, there's a way!

I think a microcontroller, even something very simple like a PICAXE would do the job.