Hey everyone, I recently got a used Thermohygrograph which was sold as not functional for just 15€. It turned out to be the batery operated kind with an electric motor driving the drum, instead of the classic mechanical drive. Which is nice, since that thing can actually be switched between 1/7/14/31 days for one drum revolution.
The circuit is incredibly simple. Just the battery, the drum motor and for each time variant one crystal, 1 or 2 15pF caps and a mystery chip WHERE THOSE DICKHEADS SCRAPED OFF THE MARKING!
I measured the signal pattern reaching the scope and it turned out to be just a simple square pulse with changing polarity (amplitude: +/- 1V (1.2, dropping to 0.8 over the pulse time) and changing delays (~4.2 secs for 24 hour mode) between pulses. The Pulse length is always identical, 48.8ms.
Since the basic circuit is always the same for each time setting the IC must be different. Does somebody know of an IC that does the described thing? I would need the 31 days version (non functional - to bad, that is THE one I would like to use) and ideally a 14 days version (which is not populated).
I attached some pictures for your reference.