Electronics

Some very interesting Raspberry Pi projects require some electronics work to get them to work properly.

My simplified electronics cheat sheet.

  • Top boards must face away from the Raspberry Pi. I don't like RPi hats because they block air flow to the CPU.

  • Solder on only one side of board; use the other side for the components

  • Wiring colors:

    • White = ground

    • Black = power

    • Yellow, Red and Blue = GPIO pins

  • Raspberry Pi GPIO pins have built in resistors - all GPIO pins REQUIRE diode or resistor

    • GPIO input should not exceed 3.3v. Use 1A, 3.3V zener diode to protect a GPIO pin from overload

    • RPi's GPIO pin -+- cathode of zener diode -- ground. The + is the input to the GPIO pin

    • Place a diode between GPIO output pin and circuit

Calculations:

  • Ohm's Law: V = I x R (voltage = current * resistance)

    • Use Ohm's Law to calculate everything

    • Resistors

      • in series

        • (2) R = (r1 x r2) / (r1 + r2)

        • (3 or more): R = r1 + r2 + r3

      • in parallel: R = 1 / ( 1/r1 + 1/r2 +1/r3)

    • Capacitors

      • in series

        • (2) C = (c1 x c2) / (c1 + c2)

        • (3 or more) C = 1 / ( 1/c1 + 1/c2 +1/c3)

      • in parallel

        • C = c1 + c2 + c3

  • Power = V x I = I**2 x R

Components:

Wire: 20 or 22 gauge

Basic Circuits:

  • Voltage divider: GND -- r1 -- Vout -- r2 -- Vin

    • r1 / (r1+r2) x Vin = Vout