My first attempt at this type of control resulted in this pair. They are played by bridging the connection between the two plates. The more contact made the higher the pitch. You can experiment with friends by making a human chain of resistance.
With a very minimal design these synthesizers are carved into a single piece of salvaged wood. Aside from the two contact plates you have a power switch and indicator light. There is 1/4\” output.
They are powered by an internal 9v battery under the left plate.