Use Raspberry Pi Python to TMP36 analog temperature sensor and MCP3008 AD converter

I wanted to get sensing data from Raspberry Pi from Node.js as well as Arduino Firmata, but it seems difficult, so I decided to go back to Python. Since GPIO of Raspberry Pi can only input digitally, TMP36 and LM35DZ AD converters such as MCP3008 and PCF8591 when using analog sensors will become necessary. Let's write a Python program that measures temperature using TMP36.

Enable SPI

[SPI (Serial Peripheral Interface)](http://ja.wikipedia.org/wiki/%E3%82%B7%E3%83%AA%E3%82%A2%E3%83%AB%E3%83% BB% E3% 83% 9A% E3% 83% AA% E3% 83% 95% E3% 82% A7% E3% 83% A9% E3% 83% AB% E3% 83% BB% E3% 82% A4% E3% 83% B3% E3% 82% BF% E3% 83% 95% E3% 82% A7% E3% 83% BC% E3% 82% B9) is one of the serial communication standards. It seems that the method of enabling SPI on Raspberry Pi has changed from 3.18 of the kernel. Raspi-config in Enabling The SPI Interface On The Raspberry Pi It describes how to use and how to enable it manually. This time we will do it manually.

Update firmware

If the kernel is not 3.18.x, update the firmware. The package has also been updated.

$ sudo apt-get update
$ sudo apt-get upgrade
$ sudo rpi-update

Check the kernel version.

$ cat /proc/version
Linux version 3.18.11+ (dc4@dc4-XPS13-9333) (gcc version 4.8.3 20140303 (prerelease) (crosstool-NG linaro-1.13.1+bzr2650 - Linaro GCC 2014.03) ) #777 PREEMPT Sat Apr 11 17:24:23 BST 2015

Edit /boot/config.txt.

$ sudo vi /boot/config.txt
dtparam=spi=on

reboot.

$ sudo reboot

SPI is now enabled.

$ lsmod | grep spi
spi_bcm2708             6018  0

Breadboard wiring

Wire the MCP3008, Raspberry Pi and FT232RL on a breadboard.

Wire with MCP3008 and Raspberry Pi.

MCP3008 VDD -> Raspberry Pi 3.3V
MCP3008 VREF -> Raspberry Pi 3.3V
MCP3008 AGND -> Raspberry Pi GND
MCP3008 CLK -> Raspberry Pi GPIO 11 (SCLK)
MCP3008 DOUT -> Raspberry Pi GPIO 9 (MISO)
MCP3008 DIN -> Raspberry Pi GPIO 10 (MOSI)
MCP3008 CS/SHDN -> Raspberry Pi GPIP 8 (CE0)
MCP3008 DGND -> Raspberry Pi GND

Wire the TMP36.

TMP36 VCC -> Raspberry Pi 3.3V
TMP36 VOUT -> MCP3008 CH0
TMP36 GND -> Raspberry Pi GND

Python installation

Install the Python development environment for Raspberry Pi.

$ sudo apt-get update
$ sudo apt-get install python-dev
$ python -V
Python 2.7.3

Install ez_setup and pip.

$ curl https://bootstrap.pypa.io/ez_setup.py -o - | sudo python
$ curl https://bootstrap.pypa.io/get-pip.py -o - | sudo python
$ pip -V
pip 6.1.1 from /usr/local/lib/python2.7/dist-packages (python 2.7)

py-spidev

Install py-spidev to operate SPI devices from Python.

$ cd
$ git clone git://github.com/doceme/py-spidev 
$ cd py-spidev
$ sudo python setup.py install
...
Writing /usr/local/lib/python2.7/dist-packages/spidev-3.0.egg-info

Sample project

Create a project.

$ mkdir -p ~/python_apps/spidev-spike
$ cd !$

Write a Python sample program by referring to the following site.

`~/python_apps/spidev-spike/spi_tmp36.py`


#!/usr/bin/env python

import time
import sys
import spidev

spi = spidev.SpiDev()
spi.open(0,0)

def readAdc(channel):
    adc = spi.xfer2([1,(8+channel)<<4,0])
    data = ((adc[1]&3) << 8) + adc[2]
    return data

def convertVolts(data):
    volts = (data * 3.3) / float(1023)
    volts = round(volts,4)
    return volts

def convertTemp(volts):
    temp = (100 * volts) - 50.0
    temp = round(temp,4)
    return temp

if __name__ == '__main__':
    try:
        while True:
            data = readAdc(0)
            print("adc  : {:8} ".format(data))
            volts = convertVolts(data)
            temp = convertTemp(volts)
            print("volts: {:8.2f}".format(volts))
            print("temp : {:8.2f}".format(temp))

            time.sleep(5)
    except KeyboardInterrupt:
        spi.close()
        sys.exit(0)

Program execution

Run a Python program. Displays the temperature in degrees Celsius at 5-second intervals.

$ python spi_tmp36.py
adc  :      232
volts:     0.75
temp :    24.84
adc  :      233
volts:     0.75
temp :    25.16
adc  :      233
volts:     0.75
temp :    25.16