- Thu Nov 27, 2008 9:20 pm
I had the EXACT same problem.
I'm beginning to suspect that the breakout board itself is designed incorrectly. I would have expected A1 and A2 on the breakout board to be wired to the "A" and "B" pins respectively. It appears they are both wired to "A" (or both to "B", but not both)
So, since I had followed the diagram on the whitepaper and put 5v on "A1", and tried to get a reading on A2... I got 5v always because there is continuity between those pads.
Perhaps someone from SparkFun can check this (HINT HINT... ANYONE THERE READING THIS?). I would not have expected continuity between A1 and A2, but I have that after soldering the sensor to the board. Meanwhile two of the pins appear to be electrically unattached to the breakout pins.
Either that or I've done something quite wrong.
In my case, to workaround, I determined which set of A/B pins were NOT wired to the breakout, and jumpered one of them to H1. This sort of works, however, the range I'm getting right at the moment is limited. I'm letting the heater run for a while, and as I do the non-alcohol reading is getting lower and lower (right now 850 out of 1024, or ~4.1 volts). If I take a swig of beer and blow across the sensor, it jumps up to 1000 (~4.8 volts) , then slowly comes back down.
These readings are with with a 100k pulldown on the output.
Why is the range still so limited for me? Not sure. I may in fact still be doing something wrong. The white paper is hard to follow, its not even clear to me how to read the resistance charts on page 2.
Also, I'm wondering if the heater is supposed to be on all the time, or is it just used to "reset" the sensor. Hmmm.. I'll have to unjumper that now to see... drat. Then again, the whitepaper has a line that says "Preheat time" is 24 hour.
Hope this helps. At the very least, investigate the A1-A2 pins on your breakout, if have continuity there and you're not expecting it.... thats probably your problem.