RPI-I2C-HUB

I2C Hub for the Raspberry Pi

Features

• I2C Hub / Repeater / Replicator / Multiplexer / De-multiplexer
  • PCA9544A IC
  • Controlled via I2C
  • Multiple part vendors
  • Devices with the same address can be attached to different ports
• Host I2 port goes to Raspberry Pi I2C lines
  • 3.3V host operation
• Four I2C slave ports
  • I2C ports can use the Raspberry Pi or have their own power (power source select jumper)
  • A Raspberry PI which runs 3.3V can control an I2C device which runs at 5V
• Voltage translation between the ports
  • I2C ports can be 3.3V or 5V
• Fits in any Raspberry Pi model
  • Cutout for Model B RCA video jack
• Interrupt controller on each channel and host 100KHz/400KHz operation
• On-board termination resistors

Testing

• PCA9544 Programming
• Run with DigIO16-I2C card on Hub Port #0
• Verify that the Hub is seen from the Raspberry Pi
• Note should be -y 0 for the older revision Raspberry Pis

pi@raspi3 ~ $ sudo i2cdetect -y 1
     0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f
00:          -- -- -- -- -- -- -- -- -- -- -- -- --
10: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
20: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
30: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
40: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
50: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
60: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
70: -- 71 -- -- -- -- -- --

• Shows that there is an I2C part at 0x71
• Next, set the mux to channel #0

pi@raspi3 ~ $ sudo i2cset -y 1 0x71 0x04 0x04

• Verify that the hub is set to the port

pi@raspi3 ~ $ sudo i2cdetect -y 1
     0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f
00:          -- -- -- -- -- -- -- -- -- -- -- -- --
10: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
20: 20 -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
30: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
40: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
50: 50 -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
60: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
70: -- 71 -- -- -- -- -- --

• This shows the two addresses of the DigIO16-I2C

• Raspberry Pi Code - Bounce a light across 8 LEDs on a MCP23017

Interrupts

• (4) Active Low Inputs
  • 3.3K pullups
• Active Low Output
  • 3.3K pullup
• On Raspberry Pi GPIO_17
  • Per Raspberry Pi > GPIO
• Each GPIO pin, when configured as a general-purpose input, can be configured as an interrupt source to the ARM.
• Test code is here

Power

• Card power is 3.3V

Connectors

J1-J4 - I2C Slave ports 0-3

1. GROUND
2. Power (see H1-H4 for explanation)
3. SDA
4. SCK
5. Interrupt*

H1-H4 - I2C power source selection

• Installed - Raspberry Pi provides 3.3V power on the I2C connector power pin
• Not installed - External device provides power on the I2C connector power pin

Factory Test

Test Setup

Test Steps

• Hook up Raspberry Pi to Ethernet
• Ethernet is using static IP
• Connect (4) I2CIO-8 cards (Rev X2 or later add Interrupt line)
• Set I2CIO-8 cards addresses to 000
• Terminator jumpers not present
• Use 5-pin 1:1 cables
• Power up the Pi (using puTTY)
• Verify all 4 I2CIO-8 cards have INT LEDs illuminated
• Log onto Pi
• Test code is here
• Enter

cd ~/RasPi/RPI-I2C-Hub/R-Hub-Intr-4x8
sudo python R-Hub-Intr-4x8.py

• Will cycle through the LEDs on all four cards
• Insert/remove slowly (every 2 secs or so) shunts on input lines of I2CIO-8 cards
• Int light will go out momentarily until message is displayed
• Messages will be like

Input changed on channel 0 value = 0
Input changed on channel 0 value = 1
Input changed on channel 1 value = 0
Input changed on channel 1 value = 2
Input changed on channel 2 value = 0
Input changed on channel 2 value = 8
Input changed on channel 3 value = 0
Input changed on channel 3 value = 4

• Verify all channels show input change (values do not matter)

Schematic

• RPI-I2C-HUB Schematic

Example Code/Driver

• Git Hub Repo

Checkout - Rev X1

• Changed base address to 0x71
• Added some extra pins marking

Assembly Sheet

• RPI-I2C-HUB Assembly Sheet