LIDAR lite and Beaglebone Black I2C signals

In my previous post about the LIDAR lite I said its I2C signals were 5V. Well, if you go to their new support page you can check in this FAQ that I was wrong. They are 3.3V.

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:

20150322_173758As 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.

Author: pedro_nf

Independent contractor on IT solutions and automation

3 thoughts on “LIDAR lite and Beaglebone Black I2C signals”

  1. Hi Pedro,

    Thank you very much for the post, I’m running your script and I get a constant output of 0x2626 doesn’t matter how much I move the sensor. I have no idea why it is responding. I did not use a level shifter like in your example. My connection are:

    BBB LIDAR Lite
    5V ——– Red
    GND ——– Black
    SCL2 (Pin 19) ——– Green
    SDA2 (Pin 20) ——– Blue

    1. Hi Tri, its been a while… check my first post on this but don’t pay attention to the use of the level converter. In my second post I explain that we really don’t need it. If I remember well, on the Lidar side I only used the power pins (power and ground) and the two I2C pins. Please check the pictures of my first post to see the used connections on the Beaglebone. Also check that on the Beaglebone side the you don’t have any cape connected to I2C and that the I2C drivers are correctly installed and configured.
      If you still have problems after checking then try with another I2C device to make sure the Beaglebone I2C bus is working.

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