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Testbench for Microcontrollers, consisting of some LEDs for digital/analog out, and a resistor ladder for analog in
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KiCad design of simple testbench for microcontrollers.

The resistor networks should be pairwise identical; I've used 680Ω for the LED resistors, with blue & green LEDs (note that the LEDs are connected to the closest pin, so top and bottom row are each connected to both resistor networks), and 1kΩ for the ladder resistors.


So what is the "ladder" part good for? It's the world's most primitive analog computer, a.k.a a voltage divider that can be used to generate a wide range of fractions of VCC, according to the formula printed on the board:

3D View

To generate a particular voltage, connect your analog input pin to one or several of the pins in the top row (next to the +) and one or several in the bottom row (next to -).

If VCC (applied to the + pin) is 5V, then

  • +1 / -1 will generate 5V * (1 / (1+1)) = 2.5V (as will +2 / -2 or +4 / -4).
  • +1 / -2 will generate 5V * (1 / (1+2)) = 1.6V.
  • +2 / -1 will generate 5V * (2 / (2+1)) = 3.2V.
  • +1 / -1,-2 will generate 5V * (1 / 1+1+2) = 1.25V.

PCB available at OSH Park

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