So the Arduino measures the voltage between alternate lines on a Vero board using a voltage divider, when a rain drop falls on the Vero board the voltage on an analogue input pin changes. I used an
A DHT11 sensor measures temperature and humidity. The Arduino code calculates the dew point and when it rises to < 4 below ambient temperature a relay switches on a supply to a pair of heating power resistors to prevent dew forming on the rain sensor and giving a false alarm.
The whole thing works really well, on my desk! I've yet to put it in the observatory. There's just one minor flaw, there is no heater feedback loop, once the humidity rises and the heaters come on, they stay on. I think I need to put the heaters in a box under the rain sensor and use another DHT11 to provide additional control of the heaters.
This is it so far:
Can anyone think of a problem that hasn't occurred to me? Yeah, I know the rain sensor plate soldering is rough! It had been a while when I did that. The final version will be neater. And yeah I know the cable feeding the secondary side of the relay contacts is too small, the final installation cable sizes will be fit for purpose!
Graeme