RPI-I2C-HUB

I2C Hub for the Raspberry Pi

Four channel I2C Multiplexer

Features

• I2C Hub / Repeater / Replicator / Multiplexer / De-multiplexer
  • PCA9544A Datasheet
  • 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
• The Raspberry Pi has 50mA max current limits
  • PCA9544 draws 11 mA (max), terminators draw 2x1mA=2mA, 2x1.5mA=3mA, total of 16mA for the card
  • Leaving 50-17 = 34 mA

Connectors

J1-J4 - I2C Slave ports 0-3

• Right angle, 0.1" pitch pins
• Pinout

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

P1 - Raspberry Pi Connector

• Card has a standard Raspberry Pi 26 pin connector which works with all Raspberry Pi models
• Card has notch for original Pi audio jack clearance

• Pins used
  • 1,17 = 3.3V (50mA max)
  • 6,9,14,20,25 = GND
  • 3 = I2C SDA
  • 5 = I2C SCL
  • 11 = INT* = GPIO_17
  • Other pins are unused

Jumpers

H1-H4 - I2C power source selection

• Installed - Raspberry Pi provides 3.3V power on the I2C connector power pin 2
• Not installed - External device provides power on the I2C connector power pin 2

Power Options

• The card has flexible power options to power external I2C interfaces
• 3.3V power to the Host Interface comes from the Raspberry Pi
  • This power can be used to drive external devices on the 4 I2C slave ports

Simple Method

• The "simplest" option is to provide 3.3V power to the external I2C from the RPI-I2C-HUB card
  • Install jumper to power the particular I2C interface from the RPI-I2C-HUB card
• Warning - The Raspberry Pi has 50mA max current limits
  • PCA9544 draws 11 mA (max), terminators draw 2x1mA=2mA, 2x1.5mA=3mA, total of 16mA for the card
  • Leaving 50-17 = 34 mA

External Power

• External interface can also have independent power
  • External interfaces can be at different voltage level from the I2C-RPT-01 card
    • Example #1: Raspberry Pi voltage is 3.3V and interface to 5V I2C interfaces
  • Remove Jumper to power from external interface (3.3V or 5V)
  • In this case, the terminators get pulled up from the external interface

I2C Termination Resistors

• Card has 3.3K Termination resistors on SDA/SCL lines

Factory Test

• Using RPI_PSOC5 Card
• Four I2CIO-8 cards
• Four 5 conductor I2C cables
• Running PuTTY
  • 115,200 baud
  • Find serial port from Device Manager
• Menu

Land Boards, LLC - RPi Card Test Station
1 - Select RPP-UIO-16 Card
2 - Select RPPSOC Card
3 - Select RASPI-PLUS-GVS-CFG Card
4 - Select RASPI-GVS Card
5 - Select RASPI-PLUS-GVS Card
6 - Select RPI-I2C-HUB Card
R - Read EEPROM
W - Write EEPROM
D - Debug card
B - Bounce LED across Card GPIOs
? - Print this menu

• Select 6 to select RPI-I2C-HUB card
• Select D to test the card access of the four I2CIO-8 cards
• Select B to bounce across LEDs
• Select T to test the Interrupt lines
• Insert/remove slowly shunts on input lines of I2CIO-8 cards
• Int light will go out momentarily and messages will be 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

Alternate 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