Arduino-based tempo/expression pedal

[Baran Ismen]

Hi.

I've come here with this crazy yet doable idea.

I've found this Behringer DW400 pedal at a rather cheap price, which is a clone of Boss AW-3. In it, there's a humanizer effect, yet It can be used either by envelope attack, or with an external pedal connection, there's no automation like auto-wah, or auto-humanize (Boss GT- series has that)

I thought that, maybe I could simulate this by using a small Arduino board. There are 2 ways.

1- There'll be one step motor and one potentiometer that will be physically connected to each other firmly. The Arduino board will include a code that moves this step motor back and forth constantly, and its speed/rate can be changed with a separate potentiometer. As this movement will turn the potentiometer, it'll affect the pedal that it's connected to.

2- There won't be any step motor or pot, there'll be just a coding that will send a voltage change to exp. pedal input of the pedal. The rate can be adjusted as mentioned above again. I'm not sure about this way, tho.

I wonder if anyone's handy with Arduino's here and may assist me for this.

[FiveseveN]

Yes, the EXP input almost certainly expects a voltage range and option 2 should work just fine. You don't need an Arduino to make an LFO though.

[Baran Ismen]

Yes, the EXP input almost certainly expects a voltage range and option 2 should work just fine. You don't need an Arduino to make an LFO though.

I have just discovered that its not something new and already been done under a name expression ramper but there seems some diy projects for that. Ill check them.

Meanwhile, any help would be appreciated. I just want to play with the rate speed, thats all, so its gonna be 1 knob and 1 switch small pedal.

Seems like mcp41010 ic is the part im looking for, its a digital potentiometer.

[ElectricDruid]

Do you mean the DW400? I can't find an "AW400". This thing:

https://mediadl.musictribe.com/media/sys_master/h2b/hed/8849375035422.pdf

There's no useful info given in the "user manual" (three pages!) about what the expression pedal input expects, so we'd have to test it. That's not hard. Put a stereo jack plug in the socket, and then get a multimeter and test different combinations of pins to see what you can find. Generally, you'll find there's two pins that provide +V (some voltage we don't know yet, but often +5V or +3.3V) and Ground, and one pin that is the input for the wiper of the expression pedal. Once you know what the voltage range it's expecting to see is, you can build whatever you like and feed it in as long as you make sure to keep it within range. E.g. you can then use the "input" pin and the "ground" pin as a control voltage input.

If that's not clear, ask.

HTH

[PRR]

Do you mean the DW400? I can't find an "AW400".

See--

"Behringer AW400 ..... ..... is a clone of Boss AW-3"

Beeringer also changed the first letter but Baran's fingers did not notice.

https://www.boss.info/global/support/by_product/aw-3/owners_manuals/

{AW2} https://elektrotanya.com/boss_autowah_aw-2.pdf/download.html

[FiveseveN]

Seems like mcp41010 ic is the part im looking for, its a digital potentiometer.

1. An Arduino (or any uC) is capable of approximating an analog voltage all by itself, see Basics of PWM and analogWrite().
2. A circuit that sweeps a voltage up and down is called an oscillator, and since in this case you'd want frequencies below audio you need a Low Frequency Oscillator. It's an elementary circuit block that you'll find in any effect with a periodic parameter change (tremolo, phaser, chorus etc.) and, once again, you don't need anything digital to implement it. It's very easy to make one with an Arduino but not if you've never used one before. And a dual op amp is much cheaper and smaller.

[Baran Ismen]

Hi.

I've come here with this crazy yet doable idea.

I've found this Behringer AW400 pedal at a rather cheap price, which is a clone of Boss AW-3. In it, there's a humanizer effect, yet It can be used either by envelope attack, or with an external pedal connection, there's no automation like auto-wah, or auto-humanize (Boss GT- series has that)

I thought that, maybe I could simulate this by using a small Arduino board. There are 2 ways.

1- There'll be one step motor and one potentiometer that will be physically connected to each other firmly. The Arduino board will include a code that moves this step motor back and forth constantly, and its speed/rate can be changed with a separate potentiometer. As this movement will turn the potentiometer, it'll affect the pedal that it's connected to.

2- There won't be any step motor or pot, there'll be just a coding that will send a voltage change to exp. pedal input of the pedal. The rate can be adjusted as mentioned above again. I'm not sure about this way, tho.

I wonder if anyone's handy with Arduino's here and may assist me for this.

Do you mean the DW400? I can't find an "AW400". This thing:

https://mediadl.musictribe.com/media/sys_master/h2b/hed/8849375035422.pdf

There's no useful info given in the "user manual" (three pages!) about what the expression pedal input expects, so we'd have to test it. That's not hard. Put a stereo jack plug in the socket, and then get a multimeter and test different combinations of pins to see what you can find. Generally, you'll find there's two pins that provide +V (some voltage we don't know yet, but often +5V or +3.3V) and Ground, and one pin that is the input for the wiper of the expression pedal. Once you know what the voltage range it's expecting to see is, you can build whatever you like and feed it in as long as you make sure to keep it within range. E.g. you can then use the "input" pin and the "ground" pin as a control voltage input.

If that's not clear, ask.

HTH

Hi, yes it's DW400, sorry. I've found out that it accepts Behringer's FCV100 pedal and it seems to have 50k pots.

[Baran Ismen]

Seems like mcp41010 ic is the part im looking for, its a digital potentiometer.

1. An Arduino (or any uC) is capable of approximating an analog voltage all by itself, see Basics of PWM and analogWrite().
2. A circuit that sweeps a voltage up and down is called an oscillator, and since in this case you'd want frequencies below audio you need a Low Frequency Oscillator. It's an elementary circuit block that you'll find in any effect with a periodic parameter change (tremolo, phaser, chorus etc.) and, once again, you don't need anything digital to implement it. It's very easy to make one with an Arduino but not if you've never used one before. And a dual op amp is much cheaper and smaller.

Would this one or this one work then? Ring on outputs seem empty, tho. A simple switch in between sine & triangle can be implemented for hard & soft transition between voltages, right? And what's the deal with 12v? TL072 can be operated under 9v afaik ?

Another thing I've noticed that, all LFO schematics I've found so far are swinging between given + and - voltages, exp. inputs are between 0v to 3.3 or 5v as far as I know.

[FiveseveN]

You would have to adapt the circuit to your particular needs, of course. Take the time to learn how it works and trivialities like power supply, output scaling and which pin the output is connected to should become obvious.

sine & triangle

Square & triangle. Very different.

[Baran Ismen]

You would have to adapt the circuit to your particular needs, of course. Take the time to learn how it works and trivialities like power supply, output scaling and which pin the output is connected to should become obvious.

sine & triangle

Square & triangle. Very different.

I seem to find various LFO circuitries around the internet, but I'm unsure about their functionalities, especially the voltages. Input should be 9V, as I plan to feed it with 9V along with other pedals on the board, and the expression output should be between 0 to 5v I suppose, that's how most exp pedals are, but after getting the pedal I plan to measure it with a 50k pot connected to it.

[potul]

Plug a stereo TRS cable into the EXP input of your pedal and measure voltages.... normally you should have a ground (generally the sleeve), a V+ and the expression voltage return (some are tip, some are ring, it depends on the pedal). It will tell you the voltage range you need, and where to apply it.

[ElectricDruid]

My own PIC-based LFO designs are pedfect for generating 0-5V control voltages. Something like the StompLFO would do the job:

https://electricdruid.net/datasheets/STOMPLFODatasheet.pdf

More details, and a couple of other options:

https://electricdruid.net/electric-druid-chips-the-next-generation/

These use the PWM-output method that has already been proposed for use with Arduino. It's essentially just a specialised and streamlined version of an "Arduino LFO".

[Baran Ismen]

I think I need to find out first whether the exp. input of the pedal is triggered with voltage or current changes. I assume its voltage based, as the FCV100 is a powered pedal itself.

It's an exact clone of Boss AW-3, so I believe if we know how Boss pedals' exp inputs work, we'd solve this as well.

[Baran Ismen]

My own PIC-based LFO designs are pedfect for generating 0-5V control voltages. Something like the StompLFO would do the job:

https://electricdruid.net/datasheets/STOMPLFODatasheet.pdf

More details, and a couple of other options:

https://electricdruid.net/electric-druid-chips-the-next-generation/

These use the PWM-output method that has already been proposed for use with Arduino. It's essentially just a specialised and streamlined version of an "Arduino LFO".

OMG, you've made your own IC's?       

[ElectricDruid]

OMG, you've made your own IC's?       

It's only a firmware program, not an IC design!
The chips are standard off-the-shelf PICs, programmed up with my own code.

[ElectricDruid]

I think I need to find out first whether the exp. input of the pedal is triggered with voltage or current changes. I assume its voltage based, as the FCV100 is a powered pedal itself.

It's an exact clone of Boss AW-3, so I believe if we know how Boss pedals' exp inputs work, we'd solve this as well.

If it is an exact clone of the Boss AW-3, then the service manual is here:

https://www.manualslib.com/download/2011487/Boss-Aw-3.html

This shows that the Expression pedal input is +3.3V, and goes to ADC inputs on the control processor. You could feed a 0-5V CV into it, as long as you scaled it down to 0-3.3V.

What's not so clear is which pin is which. Both the tip and ring are connected to the uP, so it could control them in various ways, or it could use the inputs in various ways. The sleeve connection is ground, so at least that is straightforward.

[Baran Ismen]

I think I need to find out first whether the exp. input of the pedal is triggered with voltage or current changes. I assume its voltage based, as the FCV100 is a powered pedal itself.

It's an exact clone of Boss AW-3, so I believe if we know how Boss pedals' exp inputs work, we'd solve this as well.

If it is an exact clone of the Boss AW-3, then the service manual is here:

https://www.manualslib.com/download/2011487/Boss-Aw-3.html

This shows that the Expression pedal input is +3.3V, and goes to ADC inputs on the control processor. You could feed a 0-5V CV into it, as long as you scaled it down to 0-3.3V.

What's not so clear is which pin is which. Both the tip and ring are connected to the uP, so it could control them in various ways, or it could use the inputs in various ways. The sleeve connection is ground, so at least that is straightforward.

I've just seen on YouTube that people use expression pedals with AW-3 that are not powered!

https://www.youtube.com/watch?v=-sNvbvN38Oc&t=49s
https://www.youtube.com/watch?v=Yqre-W9whj4&t=92s

[FiveseveN]

THE POWER COMES FROM THE EXPRESSION JACK
ElectricDruid explained it twice already and so has potul.

The ADC doesn't care if the voltage comes from a resistive divider (exp pedal), op amp, another microcontroller, a piezo element, photovoltaic cell, hand cranked generator etc.

[Baran Ismen]

THE POWER COMES FROM THE EXPRESSION JACK
ElectricDruid explained it twice already and so has potul.

The ADC doesn't care if the voltage comes from a resistive divider (exp pedal), op amp, another microcontroller, a piezo element, photovoltaic cell, hand cranked generator etc.

All right man, calm down :/ I just thought the vice versa (power goes from the exp pedal itself).

Assuming that I've made a basic LFO circuit and managed to work, how about disconnecting the physical connection? I mean, when I place a 3DPT or DPDT or whatever switch, can I wire it so that, when it's off, expression function of the pedal will be disabled?

[FiveseveN]

Yes. Now that you mention it, that's probably why it uses two ADC inputs: Ring (with the lower value pullup R) to detect whether a load (exp pot) is connected and Tip to measure the value (position). Unless Behringer decided to do it differently, e.g. with a switching jack. Can be easily confirmed with a resistor once you have the pedal.