I am attempting to build this circuit: https://www.instructables.com/id/H-Bridge-on-a-Breadboard/ But instead of switches, I want ldr s like this circuit: https://www.instructables.com/id/Simple-Easy-Diy-Light-Following-Robot-Without-Micr/ Both of these projects share many of the same parts so one would think this would be simple but it isn t (for me). I am using 9v from 6aaa batteries and the 2222 transistors and ldr s listed. I have a feeling my ignorance of ohms law is to blame here or my limited grasp on how to decypher a circuit diagram. I am willing to learn if you are willing to teach. "googling it" hasn t gotten me far.
From what I understand, you simply want to replace the switches in the H-Bridge circuit with a photo resistor to trigger a motor while allowing it to be reversible. I used the Falstad circuit simulator to mock up this kind of circuit and I believe it may be what you are looking for. Below is just a schematic of it.
As for the actual simulation, you can view it here. I could not find photo resistors, so I used potentiometers to mock the variable resistance of a photo resistor. To try out the circuit, use the
Resistance sliders on the right side of the simulator. You will notice that the two outputs at the bottom of the circuit, which represent the motor output, will change voltages independently as the resistance of the photo resistors change. Keep in mind simulations do not often reflect reality, in this case it did. I built the same H-bridge circuit with potentiometers and two LEDs to show motor polarity (Their terminals are swapped relative to each other). Alternating the potentiometers randomly caused the the LEDs to light one at a time with a non-zero voltage reading through both LEDs.
Interestingly, when the potentiometers were swapped out for photoresistors the whole circuit failed. The potentiometers have a max resistance of 10k while the photoresistors have a max resistance of 8k. I doubt the 2k resistance difference is what causes this, but the nature of the two resistors themselves, please correct me if I am wrong. From this, it seems like the earlier comments are correct and you will not be able to use photo resistors to control an H-Bridge.
Using a microcontroller to interpret the photo resistor values and output PWM based on these values could be a solution as well for LDR H-bridge behavior. If you would like to get a head start on figuring out how to read circuit diagrams for the future, I would recommend this thorough tutorial by SparkFun.