Hx stomp exp pedal input sample rate

[andreyOm]

Hi

 

couldn’t find an answer anywhere. 
What is the sampling rate for the expression pedal input on the stomp?

Working on some kind of LFO to control some model parameters in the hx stomp. Thought of maybe sending an analog signal into this input.

 

Thanks!

[silverhead]

I don’t think the EXP pedal is an analog audio input.

[Schmalle]

I don't know the sampling rate but it feels immediate and smooth. 

 

The expression input isn't measuring a direct voltage signal (like an audio signal) but the connected resistance between 0 and 10 kOhm (0 ... 100%). To achieve your goal you'd need some kind of controlable resistor. Something like this example of a digital 10 kOhm potentiometer. That specific electronic component can be controlled with an Arduino, Raspberry Pi or any other microcontroller that supports SPI. 

[andreyOm]

On 3/4/2025 at 8:22 PM, Schmalle said:

I don't know the sampling rate but it feels immediate and smooth. 

 

The expression input isn't measuring a direct voltage signal (like an audio signal) but the connected resistance between 0 and 10 kOhm (0 ... 100%). To achieve your goal you'd need some kind of controlable resistor. Something like this example of a digital 10 kOhm potentiometer. That specific electronic component can be controlled with an Arduino, Raspberry Pi or any other microcontroller that supports SPI. 

An expression pedal is simply a voltage divider. The hx stomp can’t actually measure resistance. It measures the voltage at the exp pedal input. So you can simply apply a voltage there that corresponds with your theoretical exp pedal position. That’s also how cv synths work.

[andreyOm]

On 3/4/2025 at 7:41 PM, silverhead said:

I don’t think the EXP pedal is an analog audio input.

I didn’t say that. But you can apply there a voltage and use it as an exp pedal

[Schmalle]

On 3/4/2025 at 7:34 PM, andreyOm said:

An expression pedal is simply a voltage divider. The hx stomp can’t actually measure resistance. It measures the voltage at the exp pedal input. So you can simply apply a voltage there that corresponds with your theoretical exp pedal position. That’s also how cv synths work.

Test your mental model of the circuit by applying a control voltage and see if you get reliable and accurate results. 

[andreyOm]

On 3/4/2025 at 10:56 PM, Schmalle said:

Test your mental model of the circuit by applying a control voltage and see if you get reliable and accurate results. 

Just tested it and it works… just don’t pass 3v or the parameter you are trying to control resets to minimum.

[Schmalle]

On 3/8/2025 at 4:48 AM, andreyOm said:

Just tested it and it works… just don’t pass 3v or the parameter you are trying to control resets to minimum.

I know that you can control it with voltage in the range of 0..3 V.

 

But I couldn't get it to work reliably and accurately with my lab power supply. I couldn't just plug in, apply 2.7 V and assume that the read value is 90%. This brought me to the conclusion that there is more stuff going on other than plain voltage reading.

 

If you can get it to go, good for you. Let me know what you did, I'm interested.

[andreyOm]

On 3/8/2025 at 7:51 AM, Schmalle said:

I know that you can control it with voltage in the range of 0..3 V.

 

But I couldn't get it to work reliably and accurately with my lab power supply. I couldn't just plug in, apply 2.7 V and assume that the read value is 90%. This brought me to the conclusion that there is more stuff going on other than plain voltage reading.

 

If you can get it to go, good for you. Let me know what you did, I'm interested.

Currently I have a limited access to an electronics lab, but from this point my options are:

1) assume that there is the other half of the voltages divider inside the helix, and calculated its value

2) go the lazy way, but make your expression pedal generic and work with any modeler:

sample the read value to some applied analog voltage at, say 100 points, and whenever you need some value in between these points do a simple linear extrapolation. You assume this should give a resolution good enough for most applications. 
 

Still didn’t have the time to test the sampling rate tho..

[Schmalle]

Ok. I figured out what threw me off so much. There is an autocalibration algorithm for the Expression Ins that has three steps:

• open circuit ( 3.25 V )
• short circuit ( 0 V )
• max. voltage / resistance (e.g. 1.62 V / 10k Ohm)

If there is no expression pedal connected (open circuit / more than 3 V are read) the recalibration is triggered. A voltage source can trigger this by providing more than 3 V, too.

The next step is to provide the min resistance / voltage (0 Ohm -> 0 V are read).

The last step is to provide the max resistance / voltage ( the standard max resistance is 10k Ohm -> 1.62 V are read). If the last step is omitted a max resistance of ~2.3k Ohm / ~0.62 V is the default.

 

It is indeed a voltage divider with an inbuild 10k Ohm resistance in series with the expression pedal.

 

You can calibrate the Expression In to any control voltage in the range of ~0.62...3 V. 

 

My multimeter isn't calibrated so values can be a bit off.

 

Correct me if there is anything wrong about this.