I am using I2C communication with the ESP32 as the master.
Do I need pull-up/pull-down resistors on the SDA and SCL lines?
I could not find anything on the datasheet that said whether there were internal pull-up/pull-down resistors.
Links to datasheets:
https://www.espressif.com/sites/default/files/documentation/esp32_datasheet_en.pdf
Do I need pull-up/pull-down resistors on the SDA and SCL lines?
Yes. 2k2-3k3 is fine.
If you're using one of the off-the-shelf I2C peripherals like the LCD display, IO expanders, etc then warning: most of them require 5V, and ESP32 runs on 3V3.
You must not connect the pullups on the ESP side to +5V, but to 3V3!
I've been using this simple voltage translation schematic with success:
"2.5V" on the left should be 3V3, of course, and the gpio numbers are wrong, but you get the idea. You can use any N MOSFET with low capacitance and threshold Vgs such that it turns on properly when about 3V Vgs. The easiest way is to search for MOSFETs with RdsON of a few ohms or tens of ohms, specified at Vgs of 2.5, and sort by price. Here's the one I'm using. Also very neat for driving loads from a 3V3 GPIO.
Since you now have two pullups on each line instead of one, it's a good idea to double the resistor value to get the same current, so 4k7 instead of 2k2 for example.
As they are GPIO pins unless specifically configured to use I2C, yes, you do need pull-up resistors.
Even if you can turn on internal pull-up resistors, it might be fine for lows speed communication, but in practice they are usually too high resistance for any real use in I2C.
As a rule of thumb I2C bus always requires 2 external pull-up resistors for the SDA & SCL lines.
Their values would depend on bus speed, voltage & capacitance (which includes both wires/trace & devices capacitance). Good starting point are usually ~2.2K for 400 kHz and 3.3V bus with a few slaves on the bus and when all are located on the same small board.
For more information on bus capacitance & resistor value calculation you can refer to this question: Is there a correct resistance value for I2C pull-up resistors?
TI has written a paper that precisely calculates the minimum and maximum values of both clock and data lines pullup resistors. These depend on the input and bus capacitances used and the supply voltage. There is no so-called rule of thumb for this!
Link to the paper: https://www.ti.com/lit/an/slva689/slva689.pdf
