Probably bad form to Necro this six year old post, but it's on the money with its description, and while hobby boards are long gone their gear lives on. Besides does it really matter when you get to our age?
I've had a similar, ongoing issue with my hobby-boards rain gauge - using Eric's counter module. Every now and then it would emit crazy rainfall levels, anywhere from 10mm to 3 metres. I know they are crazy because I'm sitting here with dry feet, plus I'm well south of the tropics.
The last one happened a couple of hours ago, under beautiful sunshine. Admittedly, a night of rain, with one 80mm odd event to make me curse again - removing that and it will tally with the analog gauge though (if I squint just right!)
Okay, some background:
Using weewx software and the owfs.py driver. 20 metre cable run, outdoor grade (silicon gel) cat 5, no hub (Bugger, fried it, still miss it.)
Bizarre readings will, would happen during actual rainfall events.
During the muggy - high humidity times immediately afterwards.
During high humidity days.
Often a series of counter rolls in one LOOP event (one read at a 20 second interval)
Or a series of consecutive LOOP reads, and then all will go quiet - crickets....
It use to be a lot worse than this but I fixed most (98%) of it by pulling the high end of the reed switch, high, by connecting it to the 5volt line. (That switching circuit consists of a 100 ohm resistor in series with the reed switch, resistor to ground and reed to counterA terminal) . Prior to that the voltage tended to float and drop to as low as 2-3 volts during some of these weird counts.
The counter module shematic on archive org...https://web.archive.org/web/20081113060625/http://www.hobby-boards.com/catalog/links/dc2.5-r1/Dual%20Counter%20v2.6%20Schematic.pdf
Long story short I still get them, even after smothering the reed switch, 100 ohm resistor, daughter board in protective lacquer - thinking it might have been a moisture issue given the high humidity clue and the fact that they were never water/moisture proofed.
I'm lucky I guess, in that I've still got hair left to pull out, but I am getting tired of chasing shadows.
The explanation I believe lies in the datasheet for the BAT54S and the 1N5819 that I used.
The 1N5819 is 400mV @100mA.
The BAT54S is 800mV @100mA.
Hence, the BAT54S, while being a Schottky diode, isn't as effective as a clamp as the 1N5819. The BAT54S could allow enough negative voltage below -0.3V that the substrate issue could occur, whereas the 1N5819 has a better chance of clamping it. It all depends on the current that the diode is absorbing during the negative transient.
That's interesting, very interesting. Could it be as simple as that I wonder. I probably need to get some and try it out I guess. I'm curious though as this isn't at the end of the line - and they are on one long line - 7 sensors with 2 counter modules scattered along its length. Should I move the counters all to the furtherest end?
Anyone got a hobby-boards 4 port hub to spare (promise I won't fry this one) - Sigh....
So, I'll get some 1N5819 diodes; but while I'm here. Any-one out there got any other suggestions?
A better switching circuit perhaps? Rather than the simple 100ohm , reed switch, in series combo. Would bounce be a problem with a reed switch? But then the counter rolls can happen when no rain is around, meaning the bucket shouldn't have tipped, ergo - no switch to bounce?
How does the value of 100 ohm sit - electronic design speaking ? Considering I'm hooked into the 5volt line now, should that be changed? The 5 volt is not the data (DQ) line, it's seperate power reseved for just this situation. (I believe it is anyway.)