Comparator circuit and 555 timer help?

Question

I want to make a solar tracking panel that my motor to rotate runs for 10 seconds and stays off for 15 minutes (555 timer?) but I don't know how to make these circuits

I will be using two pv cells at 90degres from each other that will compare voltages gathered from the suns rays, (comparator circuit) thus enabling the motor to turn whichever way it needs to, to correct its position. but only for 10 seconds

You probably need more information but that is the just of it. Any help would be great.

Answer 1

a microcontroller will likely be easier



to get direction control of a DC motor you'll probably be wanting to use a full H-Bridge (even with a uC). There are chips which are suitable for powering DC motors of a few amp. Control inputs are direction, and run.



It's possible to implement the timing characteristics using a 556 IC (that's two 555's on a single chip) Wire the two "555s" up as monostables which trigger each other. then connect the output from the quicker monostable (set up to delay for 10s) to the H-bridge's run pin

http://en.wikipedia.org/wiki/555_timer_IC#Monostable



such a circuit might start oscillating on it's own but you might need to add a start button to get it going.



direction control...

connect the comparators output to the H-bridge's direction pin

connect the PV cells to each input of the comparator.

You may need to swap which pin connects to which PV cell or the wiring to the motor- as there the possibility you might wire the motor up so it runs in the wrong direction.



NB you do know when light is shone on their P-N junctions *all* semiconductor diodes will work as tiny PV cells? with a good CMOS comparator that doesn't draw much current you probably don't need to use "proper" solar cells for light detection. a pair of LEDs should be able to generate enough voltage difference to switch the comparator



Comparators chips are often wired as open collector. That means when output is low the short the output to ground. When output is high they aren't shorting the output to ground. As such you often need to add a pull resistor to get a voltage on the comparator's output pin



Hope that helps

Answer 2

You can look up "solar tracking circuit" and see many suggestions, such as this one:



http://solartracker.greenwatts.info/solar_tracker_LM339_schematic.htm



You can also replace the two batteries with your own power supply if you want maintenance-free operation.



I wouldn't worry about cycling the power, which I presume you wanted to do in order to conserve energy. Circuits like the one above have a dead zone where both comparators are off, and thus the motor isn't consuming energy. In theory, this would even work at night, when both cells are equally dark.

Answer 3

whether you use 555's or a uprocessor, you will need the comparator ckt.

using the uprocessor gives flexibility the 555's give simplicity.



use a 555 to make one pulse every 15 minutes(you may need digital counter to get a deley this long.



use the second 555 to generate a 10 sec pulse when triggered by the first 555.

Answer 4

look into using a microprocessor and program it instead.