A touch plate for the AE Modular. You can buy the DIY kit from either of these websites:
https://smallrocks.bandcamp.com/album/biot-touch-plate-demonstration-record
https://wonkystuff.net/product/biot-kit/
This is an excellent first kit if you are new to electronic construction/soldering. Very simple and a useful addition to your AE Modular, especially if you are performing live.
Wonkystuff has done a video about the building of the kit - https://www.youtube.com/watch?v=r4GuhFDfGpg
Each input/output pairing refers to the touch plate with the same symbol; usually you will do one connection to 2 (or more) different touch plates so your finger(s) make the electrical connection. Experiment!
Patch Suggestions
It is great to add a bit of variation to any modulation as you move/press your finger (or whatever else you fancy running over the touch plates!); can be nice on filter cut off too.
Also try with the audio signal directly through it, rather than as a CV control.
See also this video from Max Richardson as a demonstration...