Raspberry Pi: Analogue Input with Gertboard (python)

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© Carelse, Pauger, Pilz 1

RASPBERRY PI

Workpackage: Analogue Input with Gertboard (python)

Description: This workpackage is about how to work with analogue input with the help of the Gertboard. We read the data of a light sensor.

Difficulty (1-10): 5

Overview: Instructions

Prepare Gertboard

Python Code

Test your Code

Circuit Schematic

Useful Resources

Requirements: Hardware: Raspberry Pi & standard equipment Gertboard Straps Jumpers Hook up Wires Resistor (47 kΩ) Light Sensor

Software: Raspbian OS python library spidev

Instructions handson.dmt.fh-joanneum.at

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ANALOGUE INPUT WITH GERTBOARD

(PYTHON) Due to the fact, that the Raspberry Pi does not have analogue inputs we have to use an extension board to get information about a light sensor or other analogue inputs.

In this worksheet we use the Gertboard. There is some python and C test code already provided which can be used.

Instructions Prepare Gertboard

- connect the Gertboard to the Raspberry Pi, be careful that the Pin 1 on the raspberry (left upper corner) is connected to the Pin 1 on the Gertboard (marked with a square)

- enable SPI o sudo nano /etc/modprobe.d/raspi-blacklist.conf o insert a # before blacklist spi-bcm2708 o sudo reboot

- install python SPI wrapper sudo apt-get install python-dev mkdir py-spidev cd py-spidev wget https://raw.github.com/doceme/py-spidev/master/setup.py wget https://raw.github.com/doceme/py-spidev/master/spidev_module.c sudo python setup.py install

- connect following with jumpers as shown in picture 1: o GP11 to SCLK o GP10 to MOSI o GP9 to MISO o GP8 to CSnA

- create circuit as seen in picture 2 o connect the blue wire to the analogue pin on Gertboard (Picture 1, upper left

corner, number 2) o connect the black wire to GND o connect the red wire to 3V

python code from time import sleep import subprocess # to prevent from spi failures reload spi drivers at the beginning unload_spi = subprocess.Popen('sudo rmmod spi_bcm2708', shell=True, stdout=subprocess.PIPE) start_spi = subprocess.Popen('sudo modprobe spi_bcm2708', shell=True, stdout=subprocess.PIPE) sleep(3) #import spidev and open SPI to work with ADC on Gertboard import spidev loops = 600 spi = spidev.SpiDev() #the ADC of the Gertboard is on SPI channel 0 spi.open(0,0)

Circuit Schematic handson.dmt.fh-joanneum.at

© Carelse, Pauger, Pilz 3

#dependend on the Pin you use on Gertboard select 0 (for AD0) or 1 (for AD1) channel = 1 #if varable loops is 600, there are 600 values printed out before the program ends while loops > 0: #send start bit, sgl/diff, odd/sign, MSBF to SPI r = spi.xfer2([1,(2+channel)<<6,0]) #spi.xfer2 returens same number of 8-bit bytes as sent #we parse out the part of bits which includes the changing value of the sensor adc_value = ((r[1]&31) << 6) + (r[2] >> 2) #print analgue value print(adc_value) # delay after each print sleep(0.05) # decrease variable loops loops -= 1

Test your Code Run your code by navigating to directory where you saved your file and typing in following command: python filename.py

Circuit Schematic

PICTURE 1: GERTBOARD

Useful Resources handson.dmt.fh-joanneum.at

© Carelse, Pauger, Pilz 4

PICTURE 2:LIGHT SENSOR

Useful Resources Gertboard User Manual:

http://dlnmh9ip6v2uc.cloudfront.net/datasheets/Dev/RPi/Gertboard_UM_with_python.pdf

Analogue Input with node.js: https://github.com/eugeneware/wiring-pi