# Multi I2C Hat for Raspberry Pi and Acme Sensor boards 

<abstract>
This article explains how to use the Multi I2C multiplex HAT for Raspberry Pi designed to connect up to 8 Acme Sensors
</abstract>

<img src="./multi-i2c_top.jpg" style="max-width:820px; width:100%;">

Create a Raspbian OS microSD with the latest lite version:

* Check this article for example: @article='cmpanel-poe_microsd'

Insert this line inside the <code>/boot/config.txt</code> file.

	# Uncomment some or all of these to enable the optional hardware interfaces
	#dtparam=i2c_arm=on
	#dtparam=i2s=on
	#dtparam=spi=on
	dtoverlay=i2c-mux,pca9548=1

Is not requested to enable the I2C using <code>raspi-config</code>

Install the i2c-tools to check the I2C bus from user space.

	$ sudo apt update
	$ sudo apt -y install i2c-tools

Check the i2c devices available by typing:

	$ i2cdetect -l

	i2c-1	i2c       	bcm2835 (i2c@7e804000)          	I2C adapter
	i2c-20	i2c       	fef04500.i2c                    	I2C adapter
	i2c-21	i2c       	fef09500.i2c                    	I2C adapter
	i2c-22	i2c       	i2c-1-mux (chan_id 0)           	I2C adapter
	i2c-23	i2c       	i2c-1-mux (chan_id 1)           	I2C adapter
	i2c-24	i2c       	i2c-1-mux (chan_id 2)           	I2C adapter
	i2c-25	i2c       	i2c-1-mux (chan_id 3)           	I2C adapter
	i2c-26	i2c       	i2c-1-mux (chan_id 4)           	I2C adapter
	i2c-27	i2c       	i2c-1-mux (chan_id 5)           	I2C adapter
	i2c-28	i2c       	i2c-1-mux (chan_id 6)           	I2C adapter
	i2c-29	i2c       	i2c-1-mux (chan_id 7)           	I2C adapter

Insert an Acme Sensor on I2C-22 connector and type:

	$ i2cdetect -y 22

	     0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f
	00:                         -- -- -- -- -- -- -- -- 
	10: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 
	20: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 
	30: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 
	40: -- -- -- -- 44 -- -- -- -- -- -- -- -- -- -- -- 
	50: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 
	60: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 
	70: UU -- -- -- -- -- -- --   

* <code>UU</code> ad address 0x70 is the address of TCA9548A mux used by the i2c-mux driver so non available to be managed 
by user space
* <code>44</code> ad address 0x44 is the address of the Acme Sensor plugged on I2C-22 Acme Sensor connector

## Schematic

* [Schematic](.//multi-i2c-schematic.pdf)

## Links
 
* [TCA9548A Low-Voltage 8-Channel I 2C Switch with Reset - Datasheet](https://www.ti.com/lit/ds/symlink/tca9548a.pdf) 
* [Raspberry Pi overlays Doc](https://github.com/raspberrypi/firmware/blob/master/boot/overlays/README)