ADXL345 accelerometer problems

[Joe Ross]

Originally Posted by Alan Anderson

We've been using an official round cable on our programming testbed for months. It wasn't until a week ago that we tried the I2C connection to an ADXL345, and it took a couple of hours of failure before I remembered some people describing making it work with a ribbon cable instead. So I repaired the KOP cable (chipped of a little plastic by accident in the process), swapped it in, and had instant success.

Which round cable didn't work? In 2009 and 2010, it was a cablestogo pn 02688. Last year it was SF Cable pn D720-03.

[rpcoe]

We have been using the round cable for testing with an ADXL345 from last year and it worked fine. Several new sensor boards did not work and I suspected that the students had connected them wrong and smoked them. As crunch time comes, I was not comfortable that we had only the old board and no new ones working. We ordered three new boards and they didn;t work either. The old board worked in two robots with the round cable. After reading this thread, we tried the flat ribbon and as was predicted here, all 6 boards work.
Anybody know why the older board works with the old cable?

Rob Coe
Mentor to Team 28

[Alan Anderson]

Originally Posted by Joe Ross

Which round cable didn't work? In 2009 and 2010, it was a cablestogo pn 02688. Last year it was SF Cable pn D720-03.

The cable I was using has no identifying marks on it that I can see. Based on the box I pulled it from it is likely one from 2010, though I can't be sure. We didn't label the ones we got in the Kit of Parts with the year we received them.

[wireties]

Originally Posted by Alan Anderson

Has anyone managed to use I2C with the original white 37-pin cable?

We are getting "real" data from the accelerometer using the molded 37-pin cable. But it is very noisy - maybe we should try a ribbon cable. It does not make obvious sense why it should matter, they are of similar length. But we will try it.

[tsaksa]

It looks like most of the common causes for this problem have been described very well, but I thought I would add one more possibility for anyone searching this thread. Our team had no connectivity to the accelerometer at first with any cable combination. It turned out that the accelerometer was responding to the alternative address even though no jumper had been added to the board. I tested the jumper with an ohm meter and did not find a short, but the device clearly acted as if it had been programmed with a jumper. If anyone else has trouble with no communications at all over I2C, try both addresses before giving up, even if there is no solder jumper on the board.