IFD:IAC WiSe22/sensors and interface schematics

From Medien Wiki

This page shows a few ways to sense touch or force and convert it to an analog voltages.

1V/Oct analog keyboard interface

This is a vintage style analog keyboard interface that is used e.g. on the stylophone to convert touches to pitches in 1V/Oct. More sophisticated version with note priority and touch/release detection can be found on music from outer space.

Velostat Pressure Sensor / Moisture-to-Voltage converter

This circuit can be used to detect finger pressure or any force on a surface with the help of a pressure sensitive sheet material called 'velotstat'. You can find a tutorial how to build the physical sensor here.

The same circuit can be used with a different type of physical interfaces as well. Instead of the velostat material as a variable resistor we can use a layout of wires known as a 'moisture sensor'. We can hookup our moisture sensor to the circuit above instead of the velostat sandwiched between two electrodes. Here is a video showing how to build a moisture sensor. Ciat Lonbarde's Tocante instrument might use this simple technique to sense touch.

By replacing the velostat or moisture sensor with a Light Dependent Resistor (LDR) you can use the same circuit to detect ambient light variations.

Frequency Detector

To convert the frequency of a musical signal to a voltage, we can use this relative simple frequency detector circuit. Note that the output is linear in frequency, so it won't match the 1V/oct input of an analog synthesizer. That means pitches will be out of tune. Their might be ways to remedy this by using a logarithmic amplifier instead of the linear amplifier in the schematic. This is shown by the next schematic.

1V/Oct frequency detector

Envelope Follower

You can use an envelope follower or envelope detector to track the loudness of a signal and use that to control e.g. the loudness of a synthesizer.