Electric Dollar Store

POT is a high-quality twist potentiometer coupled with an I²C controller which reports the instantaneous rotary position.

The I²C protocol is straightforward. The device has 255 locations. Reading from location N gives the rotary position scaled to the range (0..N). So for example reading from 100 gives a position value between 0 (fully counter-clockwise) to 100 (fully clockwise). In addition, reading from location 0 gives the knob rotation as a 16-bit unsigned value. 

import sys
import struct
import time

from i2cdriver import I2CDriver, EDS

if __name__ == '__main__':
    i2 = I2CDriver(sys.argv[1])

    d = EDS.Pot(i2)

    while 1:
        percentage = d.rd(100)
        r = d.raw()

        print("%3d/100   raw=%3d" % (percentage, r))
        time.sleep(.05)

#include <Wire.h>

byte pot_read(byte scale)
{
  Wire.beginTransmission(0x28);
  Wire.write(scale);
  Wire.endTransmission(false);
  Wire.requestFrom(0x28, 1);
  return Wire.read();
}

void setup() {
  Serial.begin(115200);
  Wire.begin();
}

void loop() {
  Serial.println(pot_read(100));
  delay(20);
}

from machine import I2C
import struct
import time

class Pot:
    """ POT is an analog knob potentiometer """
    def __init__(self, i2, a = 0x28):
        self.i2 = i2
        self.a = a

    def raw(self):
        """
        Return the current knob rotation as a 16-bit integer.
        """
        return struct.unpack("<H", self.i2.readfrom_mem(self.a, 0, 2))[0]

    def rd(self, r):
        """
        Return the current knob rotation, scaled to the range 0 .. r
        inclusive. For example rd(100) returns a value in the range 0 to 100.
        """
        return self.i2.readfrom_mem(self.a, r, 1)[0]

def main():
    i2 = I2C(1, freq = 100000)

    d = Pot(i2)

    while True:
        percentage = d.rd(100)
        print("%3d/100   raw=%3d" % (percentage, d.raw()))
        time.sleep(.05)
Default I²C address 0x28 (0b0101000)
Current consumption (typ.) 5 mA
Vcc 2.2 - 3.6 V