I2C and GPS
ben_deering at swissmail.org
Wed Nov 23 03:20:16 CET 2011
For months now I have had poor performance with my Freerunner's GPS.
The GPS problems did not seem to coincide with the two times I have
opened my Freerunner to add I2C sensors. I have an infrared thermometer
and a barometer.
Lately I have missed the GPS enough to look into the issue more. After
trying various things in software and messing with the GPS antenna, I
started to look at my sensors. The reference schematics for both
sensors call for a 100nf decoupling capacitor between ground and VDD. I
looked around in my junk bin for some. All I could find were some huge
(for the inside of a FR case) ceramic ones. They didn't seem to help.
Using frameworkd.log with the log level turned up, I was able to watch
the UBX packets as they came down and disconnecting SDA and SCL for both
sensors gave an immediate improvement in GPS reception.
I didn't notice a problem with reception when I first added the
sensors. Was anything done in software that would make I2C cause more
interference? Should I pursue the decoupling capacitors? Does it
matter what kind if they are 100nf?
Thanks for any ideas,
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