The LGE086 Touch Responsive Controller is sold as a PCB Set (LGE086 & LGE086A) and Touch Plate PCB (LGE086T). You can theoretically make is as large as you want with more PCB/Plate sets.
It’s a great way of adding “TKB” like touch control to a programmer sequencer. The circuit was originally published in Synapse Magazine in the January/February 1977 issue.
The circuit provides 8 channels of variable output voltage based on pressure, as well as 8 channels of gates relative to the 8 voltage output channels. There is also common voltage and common gate outputs
to allow the user to use it more like a traditional “keyboard” if independent outputs aren’t your thing. Or utilize both!

To quote Ken Stone’s original wright up about the design:
”Note that by itself, this project can only provide Gate signals and voltages responding to pressure being applied to the pads. There are no musically pitched voltages generated. That must be handled by external circuitry such as the programmer sequencer

This keyboard may be made with as many keys as you like, though the value of RPD (15k) may have to be made smaller as more keys are added. Each key provides for touch proportional voltage and pulse outputs. The pulse output stays high for however long the key is touched. In the schematic, each stage's touch voltages are combined through a diode network resulting in an output dominated by whichever key is touched hardest. This function is optional, but is useful if you wish to use the keyboard (in conjunction with Programmers) to play melodies with touch control of their dynamics.

How to use this module:

The keyboard may be built and installed to fit any flat surface, for example, the body of an electric guitar. Make sure that all components are mounted in close quarters with the touch keys. Wiring should be kept tight. Note that the pattern surrounding each key should be grounded. Connecting your touch responsive keyboard with a Programmer will result in an exceptionally powerful unit, able to access as many presets as you want at a touch. This means too, that your keyboard will be able to perform non-tempered scales since each of the keys can be preset to a different tuning.

A little on how it works:

On the CGS86D (LGE086A) Driver PCB: The transistors make up an emitter coupled astable oscillator with a somewhat distorted square wave output of about 100kHz. On the CGS86 (LGE086) Detector PCB: The first amplifier for each of the two stages shown a full wave rectifier and filter whose output goes positive as more of the 100 kHz is shunted to ground by touching a key. The second amplifier provides the pulse output.
The circuit may be operated with +/-12 or +/-15 volt supplies, although the output voltages will be higher on the higher supply voltage.”