Multi Channel Relay Modules

Contents:

The obective is to have a Rpi communicate with an arduino via a i2c bus. The arduino then directly controls a eight channel replay module. The interfcae should allow te RPi to turn on and off each relay and query its status. A heart beat signal will allow to maintain the health of the communications.

Raspberry Pi and 8 Channel 5V Relay Module:

GPIO Pinouts: gpio numbers for pi2

https://www.raspberrypi.org/documentation/usage/gpio/

https://pinout.xyz/pinout/pin5_gpio3

8 Channel Relay

http://wiki.sunfounder.cc/index.php?title=8_Channel_5V_Relay_Module

Python Test propgram:

#!/usr/bin/python
import RPi.GPIO as GPIO
import time

GPIO.setmode(GPIO.BCM)

# init list with pin numbers

pinList = [2, 3, 4, 17, 27, 22, 10, 9, 11, 5, 6, 13, 19, 26, 21, 20]

# loop through pins and set mode and state to 'low'

for i in pinList:
    GPIO.setup(i, GPIO.OUT)
    GPIO.output(i, GPIO.HIGH)

# time to sleep between operations in the main loop

SleepTimeL = 2

# main loop

try:
  GPIO.output(2, GPIO.LOW)
  print "ONE"
  time.sleep(SleepTimeL);
  GPIO.output(3, GPIO.LOW)
  print "TWO"
  time.sleep(SleepTimeL);
  GPIO.output(4, GPIO.LOW)
  print "THREE"
  time.sleep(SleepTimeL);
  GPIO.output(17, GPIO.LOW)
  print "FOUR"
  time.sleep(SleepTimeL);
  GPIO.output(27, GPIO.LOW)
  print "FIVE"
  time.sleep(SleepTimeL);
  GPIO.output(22, GPIO.LOW)
  print "SIX"
  time.sleep(SleepTimeL);
  GPIO.output(10, GPIO.LOW)
  print "SEVEN"
  time.sleep(SleepTimeL);
  GPIO.output(9, GPIO.LOW)
  print "EIGHT"
  time.sleep(SleepTimeL);
  GPIO.output(11, GPIO.LOW)
  print "NINE"
  time.sleep(SleepTimeL);
  GPIO.output(5, GPIO.LOW)
  print "TEN"
  time.sleep(SleepTimeL);
  GPIO.output(6, GPIO.LOW)
  print "ELEVEN"
  time.sleep(SleepTimeL);
  GPIO.output(13, GPIO.LOW)
  print "TWELVE"
  time.sleep(SleepTimeL);
  GPIO.output(19, GPIO.LOW)
  print "THIRTEEN"
  time.sleep(SleepTimeL);
  GPIO.output(26, GPIO.LOW)
  print "FOURTEEN"
  time.sleep(SleepTimeL);
  GPIO.output(21, GPIO.LOW)
  print "FIFTEEN"
  time.sleep(SleepTimeL);
  GPIO.output(20, GPIO.LOW)
  print "SIXTEEN"
  time.sleep(SleepTimeL);
  GPIO.cleanup()
  print "Good bye!"

# End program cleanly with keyboard
except KeyboardInterrupt:
  print "  Quit"

# Reset GPIO settings
  GPIO.cleanup()

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I2C Bi-directional Level Shifter

I2C bi-directional level shifter:
https://playground.arduino.cc/Main/I2CBi-directionalLevelShifter/

Sparkfun's Bi-Directional Logic Level Converter Hookup Guide:
https://learn.sparkfun.com/tutorials/bi-directional-logic-level-converter-hookup-guide

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I2C RPi to Arduino UNO Communication

How Does It Work? Is It Safe?
The Raspberry Pi is running at 3.3 Volts while the Arduino is running at 5 Volts. There are tutorials that suggest using a level converter for the I2C communication. This is NOT needed if the Raspberry Pi is running as “master” and the Arduino is running as “slave”.

The reason it works is because the Arduino does not have any pull-ups resistors installed, but the P1 header on the Raspberry Pi has 1k8 ohms resistors to the 3.3 volts power rail. Data is transmitted by pulling the lines to 0v, for a “high” logic signal. For “low” logic signal, it’s pulled up to the supply rail voltage level. Because there is no pull-up resistors in the Arduino and because 3.3 volts is within the “low” logic level range for the Arduino everything works as it should.
Source:
https://oscarliang.com/raspberry-pi-arduino-connected-i2c/

https://www.bluetin.io/interfacing/i2c-connect-raspberry-pi-arduino/

https://www.hackster.io/aardweeno/controlling-an-arduino-from-a-pi3-using-i2c-59817b

THIS METHOD DID NOT WORK!
cat /etc/modprobe.d/raspi-blacklist.conf # Remove i2c from blacklist vi /etc/modules # Load i2c.dev in module file apt install i2c-tools # Install i2c tools adduser pi i2c # Allow Pi user to access i2c devices reboot # Reboot to load i2c devices ls -l /dev/i2c* # Confirm i2c devices loaded
Source:https://oscarliang.com/raspberry-pi-arduino-connected-i2c/

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Use This method to enable i2c bus on the RPi:

Run sudo raspi-config.
Use the down arrow to select 5 Interfacing Options
Arrow down to P5 I2C.
Select yes when it asks you to enable I2C
Also select yes if it asks about automatically loading the kernel module.
Use the right arrow to select the button.
Select yes when it asks to reboot.

Source:https://learn.sparkfun.com/tutorials/raspberry-pi-spi-and-i2c-tutorial/#i2c-on-pi

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Patch Wiring Rpi to Arduino UNO

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Confirming the i2c Device is Found

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Wire Library

This library allows you to communicate with I2C / TWI devices. On the Arduino boards with the R3 layout (1.0 pinout), the SDA (data line) and SCL (clock line) are on the pin headers close to the AREF pin. The Arduino Due has two I2C / TWI interfaces SDA1 and SCL1 are near to the AREF pin and the additional one is on pins 20 and 21.

As a reference the table below shows where TWI pins are located on various Arduino boards.