Greenwatts

LM339 Solar Tracker Circuit

The LED arrangement in the LM339 circuit below uses two rows of three LEDs with each LED connected in parallel, the two rows are connected in parallel but reversed polarity. The sensor array is made with three west LEDs and three east LEDs. A 1meg resistor and a 10n ceramic capacitor (103z) are also in parallel with the sensor. The sensor LEDs provide input voltage for two comparators on the LM339 chip with the variable resistor R2 providing a "dead zone" or sensitivity adjustment. Each comparator output is fed into a transistor Darlington pair which in turn drives the DC motor. The rail voltages are provided by two batteries connected in series with the center tap providing the ground reference. We have tested this circuit with 2 single cell lithium-ion batteries providing +/- 4.2 volts and two 12 volt lead batteries, the LM339 is rated for input voltages from +/- 2 volts to +/- 18 volts.

This circuit is the result of the design efforts of Mike Mladejovsky, PhD EE. who helped us solve issues with the solar tracker #3 circuit via the Electronics Tech Online Forum which we highly recommend to anyone needing help understanding electronic circuits.