We have to do a single axis solar tracking system, we can only use resistors, capacitors, inductors, diodes, LEDs, LDRs, op-amps,transistors and servo motors do not having encoder.(It is an school project and we cant use timer because teachers dont test this device with sun, they test it with flash). We should do this in 3 parts; sensing unit,control unit, angle-adjustment unit. The angles that they want is 30,90 and 150 degrees. We will use 3 ldr and compare the intensity of light for each panel and we have to get pwm signal but we don't have any idea about how we get pmw? What can we do? If you have any idea please share with me.