The APRS logger has a number of powered analogue inputs, to which you can add a variety of sensors including most tipping bucket rain gauges which work by having a magnet pass over a magnetic reed switch every time they "tip". Basically I think this reed switch just needs to be connected between the data logger's sensor ground and one of the anemometer channels. Then you just set up a "counter channel" to count the number of pulses on that channel. This would cause the counter to increment by 0.01 every time the rain gauge tips and sends a pulse. This is a daily counter and the data logger resets it to zero at midnight (or if the data logger is powered off).
The APRS is pre-calibrated for collectors supplied by Davis (eg. the Davis 7852) but should be able to work with any collector using a magnetic reed switch.
I happen to have an old Oregon Scientific rain gauge WMR series collector which uses the same sort of tipping bucket. Not very sophisticated, but it might do till I can afford a more robust Davis collector - the information produced will only really be for interest.
Does anyone know if I can modify it for use with the APRS logger? I would obviously need to calibrate it.
Grateful if anyone is able to share any experience in this area.