Inhaos mega core, Pullup resistor on I2C bus

Other Hardware 3rd Party Boards
1

Hi,

First,
I'd like to know if there is onboard pullup resistor on inhaos mega core for I2C bus,

I've heard many version and i need to know,
So Maybe internal pullup resistor actived by wire.h library ?

Secundo,
How calculate pullup resistor for I2C bus I've 3-4 slaves on the bus, my megacore work on 3.3V level
(Megacore 3.3V, OLED SSD1306, 2x EEPROM 24LC256, GY-91)

Best regards
Bertrand

2

You have the board; measure it. Or look at the schematic (if you can find it). Further the two-wire interface does indeed activate the internal pull-ups; you have the source code :wink:
2)
TI I2CBus Pullup Resistor Calculation (pdf). There are probably more references on the web; this was the first one that showed in google.

3

Hi Sterretje,

Thanks for your answer,

Mesure Resistor on a board seems to be simple,
But is there a way to do it for internal resistor?

I added 2 pullup 1kResistors on SDA/SCL,
Is it compatible if internal pullup are actived?
Does 1k resistor is a good value?
I read .pdf, but many tutorial advice 4.7k to 10k...?

Best regards
Bertrand

4

1 kOhm should be OK from a processor perspective. It will be in parallel with the internal pull-up. Note that I'm no longer an electronics engineer and rather follow the instructions and use the indicated values.

You can't measure the internal pull-up and there is no need. If you are curious, you can try the following.

With nothing connected to the pin, add a 10 kOhm pull-down resistor; it will form a voltage divider with the internal pull-up. Power the board up with a sketch that enables the internal pull-up. Measure the voltage,; I think that that will be somewhere in the region of 1 Volt.

5

Thanks Sterretje,

All seems to go right

Best regards