Thanks for the information. This raises two more questionsHow long is a "long" wire? The RTC will be right next to the microcontroller (< 5 cm), the temperature and moisture sensors will each be about 1 m away. Is that getting long enough to matter?How can I look at the datasheets and tell if there is already a pullup resistor? If so, how do I disable it? Adding a jumper or severing a connection? Not sure if I'm brave enough for either of those
There is a schematic of that RTC module. It has 4k7 for SDA and SCL....
When you have 1 meter to a sensor and 1 meter to another sensor, you I2C bus is 2 meters long.The rule of thumb is maximum of 0.5 meters. But that depends on the used cable. A very bad cable might not even get to 0.5 meters and a very good cable (little capacitance to ground, no crosstalk between SDA and SCL) can go up to 6 meters. But don't try 6 meters, that is silly.
Nevertheless it's not meant for it, there are better protocols out there for long wires :-)
I'm interested to know what you might consider using, just for interest sake. The temperature sensors I used have I2C built in, which is why I wanted to use I2C. I could have used a serial port but that would have meant a processor co-located with each sensor to convert to serial. Have you any other suggestions?
Hardly worth fussing over.
Are you sure ? Because I could be fussing about 68 cents paying too much. This one is cheaper.