MCP3208 with RaspberryPi and Python

New version (06/2021)

I renewed this article with more information and a test program for finding adequate parameters. If you miss some information here you can find the original page in the archive [1].

Quick start

To read data from the MCP3208 with Raspberry Pi and Python:

Enable SPI through the raspi-config command in a terminal or the menu
Install spidev library for Python, if not already there [2], [3]:
```
      pip3 install spidev
```
Do the wiring [4]
Run SimpleMCP3208.py
```
       python3 SimpleMCP3208.py
```

The program reads values from 0 to 4095, referring to voltages between 0-5V at pin 0. The spi.max_speed_hz = 100kHz works well for source resistance in the range from 1kΩ to 100kΩ. If necessary, you may add a resistor to reduce input current or use an OpAmp to increase current for adequate readings.

Resistor R4 reduces voltage of DOUT to ~3.2V for RaspberryPI GPIO input on Pin 21, when working with 5V. The capacitor near VDD stabilizes MCP3208 operation. SimpleMCP3208.py:
import spidev spi = spidev.SpiDev() # Open SPI bus spi.open(0, 0) spi.max_speed_hz = 100000 def ReadChannel(channel): # read channel (0-7) from MCP3208 adc = spi.xfer([6 | (channel & 4) >> 2, (channel & 3) << 6, 0]) data = ((adc[1] & 15) << 8) + adc[2] return data for i in range(0, 10): print(ReadChannel(0))

This should get you going for simple applications. If you want to learn more about which parameters to use or what other libraries are around, hang on.

MCP3208 SPI parameters

In the code of SimpleMCP3208.py you can see the after opening the device a maximum speed of 100kHz is set. During the development of the polarimeter application [5] a suitable parameter set (max_speed, delay) was found by trial and error.

After these modifications I read reproducible values, yielding smooth curves.
I used this in my Polarimeter project on instructables[10]. The complete wiring diagram for this is available as a public project in easyeda [11].
If you are looking for higher resolution or the I2C protocol, checkout the ADS1115 page [12].
A reader from Mexico (Thanks, Pablo!) pointed out correctly, that in this setting D-out (Pin 12) connected to SPI-0 MISO (Pin 21, BCM 9) is driven with 5V, while GPIOs are specified for 3.3V only. The other connections are not affected as they are driven by the Pi. I never had an issue with my 2B, but to be safe, you can switch to 3.3V, use a level shifter [13] or add a small resistor (330 Ohms) from D-out to Ground which reduces voltage to ~3.2V. Photoresistor characteristics

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