Voltage comparator in a photo sensing circuit

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SUMMARY

The discussion centers on the operation of a voltage comparator in a photo sensing circuit. The user initially misunderstands how voltage can differ across inputs in a parallel circuit configuration. It is clarified that the varying resistance of the photodiode, influenced by ambient light and additional signals, leads to different voltage levels at the comparator inputs. This understanding resolves the user's confusion regarding the functionality of the comparator.

PREREQUISITES
  • Understanding of voltage comparators and their function in circuits
  • Basic knowledge of parallel circuit configurations
  • Familiarity with photodiodes and their behavior under varying light conditions
  • Concept of resistance variation with light intensity
NEXT STEPS
  • Study the operation of operational amplifiers in comparator circuits
  • Learn about photodiode characteristics and their applications in light sensing
  • Explore circuit design techniques for integrating voltage comparators with sensors
  • Investigate the effects of ambient light on electronic components
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Electronics enthusiasts, circuit designers, and engineers working with sensor applications and voltage comparators in photo sensing circuits.

tachyon_man
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Hello, I attached a picture below but I am confused as to how the voltage comparator is comparing the two inputs (I know how a comparator works). The test points are running down to the two inputs but wouldn't the voltage always be identical across them since voltage doesn't drop in a parallel circuit but instead if it's 12V source, there would be 12V across each 'section' in a parallel circuit. Would someone please be able to explain to me how the voltages across those can be different from each other which would then explain how the comparator is working. Thank you so much.
 

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I would presume that one branch gets ambient lighting, while the other side gets ambient plus some wanted signal? Photodiode's resistance varies with the intensity of incident light.
 
At 2:30 am this morning I realized how silly I was sounding and figured out how the voltages vary. I know exactly how this works; I don't know where I went wrong before. :D
 

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