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mcp4131

MicroPython module to control MicroChip's MC4131 SPI digital potentiometer

from machine import Pin, ADC, SPI
import mcp4131
import time
a = ADC(0)
cs = Pin(17, Pin.OUT)
s = SPI(0, sck=Pin(18), mosi=Pin(19), miso=Pin(16))
m = mcp4131.MCP4131(s, cs)

potval = m.set(0)
direction = 1
while True:
    time.sleep(.1)
    v = a.read_u16()
    print("[ %5.3f %5.3f %5.3f ]" % (0.0, 3.3*v/65536, 3.3))
    if direction == 1:
        potval = m.inc()
    else:
        potval = m.dec()
    if potval == 128:
        direction = -1
    if potval == 0:
        direction = 1

Hardware overview

The MCP4131 is a simple single-wiper 7-bit digital potentiometer controlled by an SPI interface. It has no memory settings, so will forget its current setting when it loses power.

Spec/Datasheet: mcp4131 | Microchip Technology

Methods

Creation

m = mcp4131.MCP4131(s, cs)

Takes two arguments:

s, an SPI object
cs, a Pin object for the SPI Chip Select line.

Note that on initialization, the potentiometer is set mid-way (64).

set

Set the potentiometer to a value between 0 .. 128, inclusive. Returns the value of the potentiometer:

potval = m.set(0)

get

Gets the potentiometer value, a number between 0 .. 128 inclusive.

potval = m.get()

inc

Increments the value of the wiper. Will not go past 128. Returns a value between 0 .. 128, inclusive.

potval = m.inc()

dec

Decrements the value of the wiper. Will not go past 0. Returns a value between 0 .. 128, inclusive.

potval = m.dec()

value

Synonym for get().

potval = m.value()

ratio

Simlar to get(), but returns a floating point value from 0.0 .. 1.0.

potratio = m.ratio()

Note / Caveat

The MCP4131 uses a multiplexed data in/data out pin. Reading the wiper value is quite cumbersone, so I maintain the current potentiometer wiper value in a parallel variable. get() and others merely return the value of this variable.