Oct 01, 2019· LM317, 3A adjustable voltage regulator circuit diagram Output: 1.2V to 20V, and 3V,6V,9V,12V. High quality, 3A adjustable voltage regulator. Using LM317 and 2N3055 so easy and cheap. ... Simple solar plant watering alarm. This is a simple Solar plant watering alarm circuit. It will sound alarms when the soil is dry. The trees have died.