Photoresistors
This is another analog to digital converter project using a photoresistor like I used a potentiometer in the last project.
Lessons Learned
- Resistors in a circuit don't work the way I thought they did
Resistors
I always thought resistors worked much like a hose reducer. Say you have a 2" hose with a 1 gallon per minute of water flowing through it. Now you reduce that hose to 1" with a 2" to 1" adapter. The orifice is physically 50% smaller so now you can only fit 50% as much matter through it in a given period of time. Electronics tutorials often use streams of water as an analogy for electrical current, and this makes easy sense.
So when I looked at the circuit diagram, I wondered, "why are we measuring the voltage on te circuit UPSTREAM from the photoresistor?" Wouldn't it stand to reason that you would witness the impact of the resistor downstream of the resistor? For example it doesn't make sense to measure the impact of a 2" -> 1" hose reducer on the 2" side, right?
The answer is because, as it turns out, if you take the measurement downstream of the photoresistor in this particular example, you will always read 0v. You will never see a change in the output voltage from the photoresistor. In order to see the impact of the photoresistor in the circuit, you need to measure upstream of the photoresistor.
*The face of a man who realizes he has failed*
to grasp something very fundamental
If you remember back to tutorial 4 with Analog Digital Conversion, I talked about potentiometers, and how they are a voltage divider.
Potentiometers are adjustable resistors (just like a rheostat), but with 3 pins, they're acting as two resistors in series like a voltage divider.
I used the term voltage divider there not because I actually understood what it was doing, but because that was part of the terminology used in the material I used to better understand potentiometers. And while I understand the moving the wiper changed the resistance on the output tap, and I understood that this could be described as a voltage divider, I didn't really understand what a voltage divider was, what it does, and why it does it.
A voltage divider does exactly what it says: it creates a point in the circuit at which the available voltage is equal to some portion of the input voltage, produced by dividing the input voltage across a couple of points of resistance.