25 sensors

5 rows × 5 columns

pins (`see SparkFun`_)::

  14
  23

1. phototransistor collector, to pull-up for row
2. phototransistor emitter, to ground for column
3. led anode, to limiter for row
4. led cathode, to ground for column

so…

::

   aM aN aO aP aQ cM cN cO cP cQ
   14 14 14 14 14 14 14 14 14 14 …
   23 23 23 23 23 23 23 23 23 23 …
   Mb Nb Ob Pb Qb Md Nd Od Pd Qd


      /---------- input1
   a -+-10kΩ--+- output1
   b ---220Ω--/

      /---------- input2
   c -+-10kΩ--+- output2
   d ---220Ω--/

   …
   …

   M ------------ output6
   N ------------ output7
   O ------------ output8
   P ------------ output9
   Q ------------ output10


row outputs: 05 23 19 18 26

col outputs: 17 33 16 21 22

adc inputs: 02 04 tdi/12 27 tms/14 (adc2 2 0 5 7 6)

amp: 25 (dac1) 32 (enable)

.. `see SparkFun`:
   https://learn.sparkfun.com/tutorials/qrd1114-optical-detector-hookup-guide/all


amplifier
https://learn.adafruit.com/stereo-3-7w-class-d-audio-amplifier/assembly
https://forum.arduino.cc/index.php?topic=269972.0
https://www.hackster.io/julianfschroeter/stream-your-audio-on-the-esp32-2e4661