More work on the board. The matrices were a lot of fun, and easy. The SCP barometer sensor (the green circuit board with the black circular chip) is a lot less easy in my personal experience (which isn't extensive, but grows daily.) I do intend to have this thing worked out tomorrow. Tonight was mostly making the layout look a little more eye-candy-ish for reasons that will become clear later. Level shifting for TTL is something I wish I had spent more time studying last week. I'm using a voltage divider setup to try and drag the 5v down to 3v or lower to avoid frying the chip. So each one of the 3v pins has a pair of resistors on it, which may or may not be sufficient to do the job. We're making a lot of assumptions about the impedance and whether it all works. The signaling rate of the clock line is fairly slow, 125kHz, so I think it shouldn't cause too many issues as far as the divider goes, but that's just a gut assumption and probably means squat. I haven't had formal training in this particular field, other than the School of Smoked Parts and "trial and curse." At the end of the night, I was still trying to figure out why the Arduino didn't appear to be doing any signaling, even though the main loop was toggling the chip select line just fine. In my haste I probably missed something important in the SPI setup, which I copied from the code that I used to drive the matrices, and which was based on Heather's serial EEPROM tutorial mentioned earlier in the blog here. I'd appreciate any advice, and yes, I am thinking I should wire the data ready line and forget about just timing the loop to read in the registers instead. The sensor takes about 140-500ms to return a reading and apparently only offers a narrow window to read it out of the result register. But then I'd have to muck about with either an interrupt or a condition to watch that pin, and I figured it would be best to just get it working at a reasonably basic level and refine it from there.
Off to find my earmuffs. The wind today was brutal, and my ears nearly froze off!
Curious, did you ever get this working? I am trying to interface mine with an Atmega128. Did the voltage divider work ok?
Thanks,
Serge
Posted by: Serge | June 01, 2007 at 03:04 AM