I want to drive a 12v DC motor that will rotate an array of small solar cells to track the sun across the sky. I intend to use two smaller solar cells as my sun "position sensor" by having them at an angle to each other so as the sun moves West, the output voltage will change with the motor driving the sensor to null.
I think this to be a very sluggish type system where frequencies or other gremlins will be subdued. Expected cycle time would be about 15 seconds "on" every 10 +/- minutes.
I am trying to use a change in sensor voltage of about 0.015v (between pins 2 and 3) to operate the Op-Amp with a sensor voltage range of about 2.5 to 3.5 volts. The output of the Op Amp will turn on a Mosfet that triggers at about 3.8V to power a relay to the drive motor.
Pins 1 and 4 are grounded, pin 8 is 16.5 volt supply and pin 7 is the output. I have a voltage divider network on the inputs to reduce gain to 379 = (49300/130) * (.015). Pins 5 and 6 are not used.
My problem is that the op Amp is saturated to rail voltage no matter what the input differential voltage is. If I put a pot on the rail voltage to vary the output to the Mosfet, the relay picks up as intended when output voltage exceeds 3.8 volts. Also there is a desired hysteresis effect on the Mosfet varying the output voltage using the pot.
- Is it possible that the "sensor cells" I am using do not have the current output to drive the Schmidt trigger?
- Any other comments, ideas and help will be appreciated.