Knob + ADC board

The knob + ADC board pairs a potentiometer with an MCP3008 ADC, the wiper on channel 0 and the reference tied to the 3.3 V supply, so the Pi can read a knob at all. It costs $9 and is for any analog control: menus, setpoints, dimmers, thresholds. Wire the four SPI pins plus power and ground, then read channel 0.

What's inside

• The potentiometer is a divider across the 3.3 V rail; its wiper delivers 0–3.3 V as you turn it.
• The MCP3008 digitises that voltage to 10 bits over SPI — the Pi itself has no analog inputs.

The board joins the ADC's two grounds and ties VREF to VDD, so vdd must be 3.3 V and the full scale is 3.3 V. The kit has no chain ends; the SPI pins are clk, dout, din and cs.

Wiring it in circuit.py

from wiring import *

pi = Pi()
knob = kits.KnobADC()

pi.V3_3 >> knob.vdd
knob.gnd >> pi.GND
pi.SCLK >> knob.clk
pi.MISO >> knob.dout
pi.MOSI >> knob.din
pi.CE0 >> knob.cs

Driving it in main.py

from gpiozero import MCP3008
from time import sleep

knob = MCP3008(channel=0)

while True:
    print(f"knob {knob.value * 100:.0f}%")
    sleep(0.5)

Why buy the kit

The loose pot and MCP3008 cost $1.50 + $4 = $5.50, against $9 — $3.50 for the five internal wires (wiper, reference, two grounds, power) done correctly. The MCP3008's breadboard wiring is where beginners go wrong: VREF left floating and a ground missed both give nonsense readings, and the kit cannot have either problem.

Simulator vs real hardware

• The knob's position is a datafeed field in percent; the wiper voltage follows it, the ADC quantises to 10 bits with the chip's noise and non-linearity, and value comes back 0.0–1.0.
• The stock MCP3008 is powered from 3.3 V here, as the kit intends; running a bare chip from 5 V would put 5 V on the Pi's MISO pin.
• The SPI bus is simulated at the transaction level, so gpiozero.MCP3008 runs unmodified; the same program works on a real Pi wired the same way.

Further reading

• gpiozero: MCP3008 — channel, value, voltage and the SPI wiring conventions.