“This project is based on a 20X2 PICAXE Microcontroller. It uses a programmable timing circuit to allow the user to program repeated automatic plant watering cycles by controlling a small electric pump that feeds the plant water with 1/4 ” tubing. The water reservoir can be anything you like such as a plastic bottle or rain barrel. For this particular version you need 120VAC power, but you could conceivably convert this to battery or solar power. This is a prototype and could also be reduced in size considerably in future versions.
The ideal use for this, and the reason I designed and built it, is to water plants in a plant pot to keep them alive for a few days while you are away on vacation or otherwise occupied. This is actually the second version of this project. The first version was very simple, based on the 08M2 PICAXE, it had no display and was not programmable by the user unless they had the knowledge and tools to change the program code. This new version is much more friendly and allows the user to program in the desired volume of water and time between watering with a potentiometer and set button and then displays the settings and timing status on a 2X16 LCD.
The program puts arbitrary but sensible limits on the volume of water and time. I limited the time to 72 hrs or 3 days, figuring that most plants would need a drink after 3 days. Also water volume is limited to 2.5 liters. Partly this is also to make the math on the microcontroller easier. Large numbers are more difficult to manipulate on the PICAXE because word variable size is limited to 64,000. Regardless, there is nothing stopping you from editing the program to expand these limits if you want to.”