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January 5, 2010
Python, C, C++, Fortran, Brainf..k,
about 2 years ago
Right now I’m running mine off about 30 meters of cable. I’m using an Arduino. I’ve noticed that if I power the Arduino off my laptop’s USB port (rather than a wall transformer) I have trouble.
The first of these sensors lasted about a year and then started to drift. Saturated humidity remained, but lower humidities started to show higher and higher frequencies. I replaced it in mid-September 2012.
about 3 years ago
I’ve been running my BMP085 off the +5 volt rail inadvertently for over a month. I’m not proud of the fact that I can’t read a data sheet. But, I will say that it has been working. I did have a strange anomaly come up last night on my weather station, where the BMP085 lives. When the pressure was rising and the temperature was falling, all of a sudden the pressure jumped about 350 Pa and then as the temperature came back up and the pressure fell, the jump reversed itself. Odd. I’m going to implement Member #236519’s suggestion. Go see KWIAPPLE11 on Weather Underground. That’s me.
about 3 years ago
Having written the above a week ago, I wanted to follow-up. While the cal data in the device seemed wrong, I was able to figure out cal data on my own. With that, I’ve had really good luck. The frequency drift went away when I moved the sensor away from my laptop and hooked it up to another PC. I don’t have a root cause as to why. Go to weather underground, look for weather station KWIAPPLE11! My sensor is at 100% RH at about 7925 Hz. At 0% RH I’m at 6565 Hz. I got this by comparing my measured RH with data from a nearby weather station. Plot frequency versus RH. Write the equation!
I spent several hours trying to get mine to work to no avail. I saw someone mention that they got one that had bad cal constants in EEPROM (I’m reading 0s out of the four bytes where the cal constants should be). I ordered another one to see if it has the same problem. I’m also seeing that on about 10 feet of twisted pair (with the other line at +3.3V), the frequency isn’t stable – it drifts by a 1000 Hz in a stable atmosphere. The output impedance of the circuit looks like 1k, so that’s confusing – I’d expect that would be enough drive. When I get a chance to put it on a scope, I want to see what the signal looks like at the micro. As an aside, the BMP-085 I have is stellar.
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