I2C SCL line not producing any signal


Here is my question:

When I use the Wire.h library to connect to an I2C device, I should have a consistent 100kHz signal coming from my SCL pin, correct?


I have been unable to control my I2C device (an NS73M FM transmitter from SparkFun). I have been trying to isolate the issue, and I believe I may have found the problem.

When I use an oscilloscope on the SCL pin, I see nothing (i.e. 140 mV DC). When I do the same on the SDA pin, I see a consistent 62.5kHz signal which has a peak to peak voltage of 1V.

I should mention that I am using an Arduino Uno R2, so my SDA is pin A4, and my SCL is pin A5.

This isn't what I expected at all. I would think that when nothing is being transmitted The data pin would transmit nothing, and the clock would produce a constant frequency (at 100kHz). Do you think I have a defective board, or am I doing something else wrong.

I can provide more data if you ask for it.

There is no clock if there is no data transfer occurring.

Nick Gammon has a great write up on it here.

Thank you for the pointer. That is an incredibly helpful write up.