How to Make an Impact Sensor with MPR121 for an Electronic Santur?

[hsoft_project]

Hello everyone,

I am working on an electronic Santur (a Persian hammered dulcimer) and need help designing an impact-sensitive sensor using the MPR121 capacitive touch controller. My goal is to detect both the intensity (force) and occurrence of hammer strikes on the sensor.

The problem:
The MPR121 works perfectly when I touch the sensor with my hand, but it does not detect hammer strikes (mallet hits) properly. I have tried different configurations, but the sensor does not respond well to non-conductive objects like my mallet. I need a way to make the sensor detect hits from external objects (mallets, sticks, or any non-human conductor) without requiring direct hand contact.

Current setup:

• MPR121 with custom capacitive touch sensor: Two aluminum foils with a thin plastic sheet between them.
• ESP32 microcontroller handling the I2C communication.
• Threshold values adjusted, but still ineffective for hammer strikes.

What I have tried so far:

1. Lowering the Touch and Release Thresholds (Touch: 6, Release: 3).
2. Adjusting Charge Time to improve sensitivity.
3. Adding a floating ground to improve capacitive response.
4. Changing the sensor material (thin copper tape, aluminum foil).
5. Modifying the debounce settings for better impact detection.

What I need help with:

• How can I modify my capacitive sensor design so that it reacts to hammer strikes and not just hand touch?
• Are there any circuit modifications or material changes that could improve sensitivity to external impacts?
• Would an alternative approach (such as combining capacitive sensing with piezoelectric sensors) be more effective?

Any advice, suggestions, or alternative sensor recommendations would be greatly appreciated!
Thank you in advance!

[JP-Stereo]

Hi, it seem that this sensor is driven mainly by capacitance changes.
It's interaction with hands must be induced by the water content or the density of the human tissus.

It is also stated that the response threshold can be adjusted according to the application.

So you must incorporate a compatible material in the mallet and adjust the device accordingly.
The sensor manufacturer should happily provide you with direct information, no FAFO...

Good luck.

[glebert]

My intial reaction was the same as the response you got at electronics stackexchange in that a piezo would be a better input sensor. You seem only interested in capacitive sensors but don't say why. Maybe you can explain a little bit why you want to use capacitive sensors even though they don't do well with inputs like mallets. I'm assuming that this won't have strings, just sensors. For playing santur is string muting critical so detecting finger touch is as much a necessity as the striking input?