I2C and GPS
ben_deering at swissmail.org
Thu Jan 12 00:00:40 CET 2012
I promised myself that I wouldn't take my FR apart again until it was
time to install the GTA04 board so I won't have pics of what I did this
weekend, but I can share some other info.
BMP085 barometer install pics:
MLX90614 thermometer install pics:
Adding i2c devices to a Freerunner is fairly easy. There are only 4
wires and as long as there aren't address conflicts, you can just keep
adding more devices. Here is where you can find a picture of where to
attach the wires:
The change I made this weekend was to stand an SMD resistor up
vertically on the SCL test pad (If you look at the pictures I link
above, that is where the orange wire attaches to the board) in the FR
and solder it. I then attached the SCL wires for my 2 sensors to the
top of the resistor. I used 4.7k ohm which is probably more than I
should have used, but it works. I think 1K might make more sense, there
was some mention of adding series resistors for long i2c circuits,
though each of my SCL wires is 8 cm at the most.
Sorry for the lack of pictures of the current state, but the way I
crammed the BMP085 in is fragile and I don't want to break it. I hope
my description along with the other pics makes it clear enough.
As for schematics, i2c is just 4 wires
VDD -> voltage source on the AUX button
GND -> ground side of the clock battery (supercap in my case)
SDA -> SDA test pad near the debug connector
SCL -> 4.7k resistor ->SCL test pad near the debug connector
The reference implementation for the 2 sensors I installed was a little
more complicated with pullup resistors and decoupling capacitors, but
everything seems to work without them.
On 01/11/2012 07:46 AM, David Matthews wrote:
>> can we have a picture of the final tweak� please ?
> +1 yes please! I'm struggling to understand what you've done, but ity
> sounds like something
> I'd be very please to have.
> and by the way that stuff I wrote earlier about sdcards was garbage -
> it was
> a faulty card, not a problem with qtmoko or shr
> For me now first thoughts when I see an sdcard problem are that either
> card is faulty or inherantly incompatible with the freerunner (and
> that seems
> very common)
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