Assignment 5: Quirky Circuit


For my assignment, I wanted to make something unique but also practical. The initial idea I had outlined was a switch that did not exclusively need human manipulation to work and could be tweaked to work automatically. My first thought was a circuit involving a photo sensor.


In class, we talked about photoresistors on Tuesday and that gave me the idea to build a circuit with a photoresistor. The dynamic resistivity of these special devices allowed them to ‘open’ and ‘close’ the circuit depending upon the light conditions. So, I came up with the idea of connecting the photoresistor in a circuit so that other parts of the circuit (in my case an LED) would turn on when there was adequate light shining on the photoresistor (the resistance would be very low in this case) and then turn off once the light level reduced (causing the resistance of the photoresistor to shoot up to some absurdly high level). This type of circuit could be used to automate street lights (with a reversed mechanism obviously) to turn off lights during the day and turn them on in the evening.


The photoresistor that I used:

LED on in adequate light:

LED turned off in lower light conditions:



During my experiment, I realized the circuit was not going to be perfect in the real world. although theoretically, in zero light conditions, the resistivity in the photoresistor would approach a near-infinite level, however not only is that impossible in real life, there was ambient light all around the IM lab where I was doing the experiment. It led to the LED being faintly lit even when the circuit was supposed to be ‘open’.

In the future, I will have to link the photoresistor to perhaps a mechanical device like a servo that can physically open the circuit or close it depending on the current passing through the wire.

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