need help on a solar tracker circuit

the circuit works but I am not that well versed in op-amp configurations. I am using two GaP led sensors (4 LEDs in paralell on each input) which feeds a voltage comparator which in turn drives a push/pull transistor pair (think thats the correct term) which gives directional control to a dc motor. The circuit works well but I have a problem in that the voltage output of the op-amp swings positive to slowly causing the circuit to use more power than I think it should. The circuit is designed to be very simplistic and I would like to keep it that way (as few components as possible)

**broken link removed**

sry I guess I should post some component values... 4558DX General Purpose Op-Amp, D2058/NTE377 NPN Transistor, B601/NTE262 PNP Transistor, Zener Diode - 5.6v, R1 - 10meg, R2 - 5meg, R3 - 20k-ohm, R4 - 10k-ohm, LEDs - clear lens GaP green 5mm 40deg, power supply 24volts (+12/-12)

You can't have that diode on the motor, it'll forward-bias when the motor's reversed. You'll need to move that protection over to the transistors themselves.

The circuit's theory has problems. Motors should generally not be controlled by an analog voltage like this. It's inefficient, heats up the transistors, and tends to stall the motor.

What you need is a comparator with 3 states- forward, reverse, or nothing. And there needs to be some form of hysteresis to keep from oscillating between forward and reverse, hunting for something "perfect". The Stop state needs to exist for MINOR imbalances in East/West signal, because when you stop when equal, with high gain, minor fluctuations in East/West signal will cause it to be in constant, pointless motion. More like "ok, if East is SIGNIFICANTLY greater than West, move Forward, then Stop once East isn't SIGNIFICANTLY greater than West. Even if West becomes slightly greater than East, don't start moving Reverse for that".

Thanks Oznog ... the circuit has to be as simple as possible ... it may not be ideal but it works... the diode on the motor was a mistake I will update the schem... I am looking for some suggestions on how to modify it to overcome the shortfalls you have pointed out.

The circuit also has another fundamental flaw. Read Rule of thumb #3 in this**broken link removed**

I got interested in the using LEDs as photo-detectors. I tried some moderately bright red LEDs that I have laying around, similar to these. They are in a water-clear T1 3/4 lens. I do not know their viewing angle; i'm guessing they are the 30 degree variety, because they were bought for indicators.

Shunting an unbiased LED with a 1megΩ resistor, under outdoor illumination on a very cloudy day, I get about +350mV anode to cathode, using a Fluke 73 DMM (>10meg input impedance). The LED is directive, consistent with the "viewing angle" shown on the referenced data sheet.

I then connected two LEDs in parallel, which approximately doubled the output voltage, indicating that the current produced by the LED (into the 1megΩ resistor) also doubled. I then reversed one of the LEDs so that the pair is connected in inverse parallel with the 1megΩ resistor, and bent their leads so that their optical axes diverged by about 45 degrees.

The 2 LED array produces +- 200mV as the array is panned across the sun, with zero volts out when the optical axes of the two LEDs roughly bisects the angle formed by the two axes. Seems like this could be used to drive a solar seeker, because the 2 lLED array puts out a signal which goes from +200mV to zero to -200mV as the sun angle changes.

PS: The sky just cleared, and I took the array outside again. Here at 42degrees North Latitude, I was able to get the output to go from -1.4V to +1.4V by pointing first one LED and then the other at the sun.

I cant see how the circuit broke rule#3 as the LEDs are operating in solar cell mode as voltage generating devices?... interesting idea placing the LEDs in a inverse parallel configuration I think I will def give that setup a try... maybe feed it into a flip/flop op-amp arrangement... you also have to remember that the sensor also must reset the tracker to east in the morning and be able to regain alignment after cloudy periods...

It's too bad the Moderator didn't lock out one of the two crossposts early on, now I don't know which one to reply too.

Here is a minimalistic solar tracker.

It controls azimuth and elevation and contains a homing circuit with a timer to select duration of twilight up 60 degrees latitude.

Boncuk

yea minimalistic... if anyone can contact a moderator I would prefer that this thread be removed as I have (by mistake) cross posted in the renewable energy forum