RainCheck GSM

My friend owns a garden which is located away by about 30 min. of car drive. The location is without electricity but there's a drilled well so plants can be irrigated with using an electric water pump and an Generator.

We need to know if there was a rain in last 24 hours, and how long it last, so that in case of enough rain, it will not be necessary to travel to irrigate the plants. By that, result is less driven kilometers, less consumption (and less social contacts).

High level: Solution is to use an Arduino based rain sensor and an GSM module with small pre-paid subscription to inform daily about previous day's amount of rain. Presence of rain is measured in 30 minute interval and summary of measured data is being sent on adjustable requested time (noon).

Lower level: At start, Arduino will get the time from GSM. As rain measure is planned on each half and whole hour, Arduino it will calculate the initial delay until next measuring time. There is a designed (adjustable) time when Arduino will send out the measured data report - at noon of the day. Report will be sent as GSM SMS message. As GSM module is energy consumptive, it will be powered on only on demand - once at the start to get the initial time, another time when it will send the data. Rest of time it will sleep.

To measure rain presence, we will use an simple rain sensor attached to Arduino's analoguw pin. The sensor must be placed at least 45 degree (better more) to allow rain drops flow off the sensor to prevent false alarms. Preferrably sensor should face the south-west direction to allow sun to dry up the surface as fast as possible. Each half hour the we will check the sensor state, whether it does report rain or not. The value will be attached to SMS and stored in memory. At the end of measuring cycle (usually 24 hours) we will send the collected data as an SMS message to recipients mobile.

After sending the SMS, the program will power off the GSM and restart the Arduino. A daily reboot would prevent freezing issues and will clear the memory thus watchdog will not be necessary.

It must be tested what kind of battery will be sufficient to provide enough power for whole solution. Assuming to use an motocycle battery on 6 Volt or car battery on 12 Volt, both could be charged from Generator during water pumping.