Is there a benefit to using a Trinket for counting the tips instead of using the Mayfly? I’ve built a bunch of tipping bucket recorders using only Mayfly boards by just connecting the bucket’s reed switch to the Mayfly pin D10 and using code to look for an interrupt to wake the Mayfly, increment the count, and go back to sleep. It records and transmits (via 900mhz Xbee) the count every 5 minutes, and resets the daily total at midnight. I’m guessing the Trinket is there so that you don’t miss counting a tip that comes in while the Mayfly is busy doing an uninterruptible time-consuming function, like transmitting the data via cell?
What kind of heater power are you using (AC or DC?), and what circuitry is controlling the heater on-off functionality? Are the ones recording the bad tips equipped with heaters or not? I’d remove the rain gauge reed switch wires from the Trinket so there’s no input at all to the Trinket, and then see if it continues recording phantom tips or not. If it is still recording bad tips, then your problem is with the Trinket. If the bad tips stop, then your problem is likely in the wires going to the gauge (a short somewhere, corrosion, or RFI or other signal interference) or with the reed switch failing (which I’ve seen before).