Simple solar tracker with stepper motor

Thread Starter


Joined Sep 19, 2010
There is a attached circuit to make run stepper motor continuously. 2 LDRs can be replaced with Forwd and Back-Wrd switches by separating then with a paper card. But where to fix another LDR to disable the circuit when sun hides?

Thanks in advance.



Joined Aug 7, 2008
That is one wierd circuit- or maybe I've lost a few more marbles. If you have two LDR's, then you can tell if it is dark.


Joined Sep 8, 2011
Fun fact: It seems the te555-1 is a rebranded pic 12f629. That explains the 7805 regulator.

Unfortunately you can't just replace the switches with ldr's because they're not switches, they're light dependent variable resistors. I'm not saying it can't be done, it's just more complex than that.

case in point:


Joined Sep 26, 2009
it also looks like they are multiplexing 2 of the stepper outputs as the switch inputs in the stepper motor controller circuit, so, just replacing them with an LDR could really cause some issues with the step logic of the motor... what you would need is an entirely different circuit that can "emulate" the switch press, you can use a comparator circuit with the LDR's and just have the comparator close some small SPST relays.... that way you can also build in some hysteresis or have a "window" into the circuit to where if either LDR has any light, then the comparator just doesn't do anything....


Joined Aug 7, 2008
A speculative outline: Sample LDR " JEM Cell " , 1k to +5 V & cell, other cell lead to gnd. No cover- .64V; one semi transparent cover-1.27V;2 covers-2.0V; dark-3. V, [ cell Vs]. U1, C, comparator gives direction; U2, I, invertor. U3 & U4, with U5, gives a drive signal if cells are suficently unbalanced, if low = stop. U8 detects darkness. Looks like we need another IC to make sure that both cells are high. The idea is that if the cells are ballanced and are illuminated, motor is off. If cells are un ballanced & illuminated, then either A or B will be high, motor will run. If cells are both dark- motor off. Pos input to U5 is about 1/2V.


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