If you connect 5V to any of the 3.3V pins of the Beaglebone you will probably kill it so just to make sure I power up my Rigol scope (I got it after listening to this eevblog review, thanks Dave;-) and check the voltage on one of the I2C pins of the LIDAR lite. Humm… in the unconnected pin I have 3.6V. A little higher then 3.3V. Lets check the Beaglebone absolute maximum ratings. I’m using the I2C2 pins (connector P9, pins 19 and 20). From the Beaglebone electronic diagram they go into the TI AM3358 processor. In the AM3358 datasheet I see that the maximum voltage is 3.8V… we are pretty close to the maximum but it should be ok. This is the processor chip so we need to be careful! If I measure the voltage on the I2C2 Beaglebone side (unconnected pins) I get 3.2V.
So now I connect the LIDAR lite directly to my Beaglebone and… it still works! And no smoke from the Beaglebone or LIDAR lite :-) This is a picture of the I2C data pin:
As the LIDAR lite has a 4.7K ohm pullup resistor, according to their documentation, I didn’t use any external pull up resistor. We are pretty close to the 3.8V maximum thought… I’ll check with the Pulsedlight support team why is this signal so high.