Lesson 03 - I2C II
The lecture
This is the second of two lectures about I2C and components on the I2C bus
I2C (or wire) is a very common local network or fieldbus within robotics and controlsystems.
Today is dedicated to
finalize exercises from last time
remember: timing and performance
Interfacing to real I2C slaves
Interfacing I2C interfaced temperatur sensor TC74
Interfacing I2C interfaced audio volume potentiometer DS1807
The lecture will be short because exercise will be of high priority today
Preparation for the lecture
Finalize exercises from first I2C lecture
Read litterature from last tiome with focus on slave functionallity
Use datasheets for the exercises
Exercise 2 - DS1807 - digital potentiometer
Which commands are avilable
including parameters
Do blackboard design
Do real design
Exercise 2 - TC87 - temperature measurement
Design Master code for handling
TC87
Which commands are available
You r(subset) of implementation
Code it
Exercise 3 - DS 1307 realtime clock - EXTRA
As exercises above
Exercise 4 - you slave framework
Based on exercises from previous lecture design a framework for a generic slave
ID
ID of operations read and or write
how to you carry out a read from a specific register in the slave device
same just for write
Code is on your Arduino
It is an idea to have one command (read I assume) that can return status and ID from slave device
independent
Litterature and slides
Slides
slides here from last time
Litt and data sheets
Repetition
Litterature from previous lecture
Movies
After today - you should (at least) be able to …
Understand I2C protocol
Be able to design a master slave protocol on top of I2C
Code it and get it running
Understand timing and performance on the I2C bus
Tips
3.3V versus 5V
Some devices like Arduino UNO, Mega,… is powered by 5V.
See more here (a practical viewpoint)
Other devices like esp32, m5stack etc is running on 3.3V
This might give problems when having a mix of 3.3V and 5V devices on the bus
You might damage 3.3V devices by having a 5V device on the canbus.
meaning you might be lucky or … not.
citing from element14.com
2C devices have open-drain drivers, which only pull the SCL and SDA lines low to 0V.
Each I2C line should have a single pull-up resistor: make sure they pull up to 3.3V and not 5V.
Also make sure that each 5V part has a reasonable Vih (Input voltage high) threshold.
Many 5V chips use TTL Vih which is 2.0V, which works.
Others may have Vih = 0.7 x 5.0 = 3.5V, which means you'll have to do something else.
A hack
disable internal pullup resistors in the 5V based device and use eternal pullup resistors connected to a 3.3V source. You might be lucky because
citing hackaday (link above)
3.3V TTL logic shares the 0.8V and 2V thresholds for logic 0 and logic 1 transitions with 5V TTL logic,
so a 3.3V TTL output can drive a 5V TTL input without any extra hardware required.
But I dont give any guarantee
Ground
When wiring up always start with ground so all devices has same reference
I2C recover
If your I2C locks up this code might help you lect03-i2c-recover