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micropython-MCP3001

MicroPython library for the MCP3001 10-bit 1-channel SPI Analogue-Digital converter

This library enables an MCP3001 ADC to be used with any MicroPython implementation that supports SPI. Almost all MicroPython-capable boards have adequate ADCs onboard, so you might only want to use this library if:

• your board has no ADC (like the Wemos W600-PICO) or a very limited one (as on the ESP8266); or

• you wish to use an external reference voltage source such as an LM4040.

Installation

Copy the mcp3001.py file to your MicroPython board's filesystem, typically to the root or /lib folder.

Usage

import mcp3001
# …
adc = mcp3001.MCP3001(spi, cs)

Initialization

MCP3001(spi, cs [, ref_voltage])

• spi is an instance of a Serial Peripheral Interface bus object, for example spi = machine.SPI(0)

• cs is an instance of an I/O pin object, configured for output and ideally initially set high. An example might be cs = machine.Pin(17, machine.Pin.OUT, value=1)

• ref_voltage is an optional argument to manually set the reference voltage. If it is not specified as a float, the value of 3.3 is assumed.

Methods

• read() — returns an integer ADC reading from 0–1023.

• read_u16() — returns an integer ADC reading from 0—65535. This is provided for compatibility with MicroPython's method of the same name.

• read_v() — returns a floating-point ADC reading from 0.0 – reference voltage volts.

• reference_voltage() — returns the ADC reference voltage as a floating-point value. Returns 3.3 if none was given during initialization.

Example

An MCP3001 is used to read the value of a potentiometer into a Raspberry Pi Pico. The brown wires in the diagram indicate analogue ground, and have been kept separate from the black system ground wires. If your board doesn't have a separate AGND connection, a regular GND connection will do.

The default SPI(0) pins have been used on the Raspberry Pi Pico: GP16 for RX, GP17 for CSn and GP18 for SCK. In the absence of an external reference voltage, 3V3(OUT) has been connected to V_REF on the MCP3001.

<img src="img/Pico-MCP3001_bb.jpg" width="704" height="416" alt="image of an electronics breadboard, with a green Raspberry Pi Pico board connected to an 8-pin MCP3001 ADC chip, with the output of a small blue potentiometer being fed into the ADC input" />

Code: test_mcp3001.py

Device information

Datasheet: MicroChip MCP3001 2.7V 10-Bit A/D Converter with SPI™ Serial Interface

Pinout

1. V_REF — analogue reference voltage. Should not exceed V_DD.

2. IN+ — Positive analogue input. While IN+ and IN- form a pseudo-differential pair, they can't float completely unrelated to system voltages. Please refer to the datasheet.

3. IN- — Negative analogue input. Typically connected to V_SS, or analogue ground (AGND) if your micro-controller has it.

4. V_SS — Ground.

5. <span style="text-decoration: overline;">CS</span>/SHDN — SPI Chip Select (active low) and combined ADC shutdown line.

6. D_OUT — SPI serial data out.

7. CLK — SPI serial data clock.

8. V_DD — power supply, 2.7–5.5 V DC.

Note that the MCP3001, unlike other chips in the MCP300x range, has no SPI D_IN pin. Its entire operation is controlled by the <span style="text-decoration: overline;">CS</span>/SHDN pin, and only the data out and clock lines are used.

Credits

© Stewart Russell — scruss.com, 2024.

Based on Romilly Cocking's mcp3008.py library.