From b2294b6dc7695102bd02d36b05183478d8aa00d2 Mon Sep 17 00:00:00 2001 From: Andrew Kesterson Date: Thu, 4 Jun 2026 13:22:25 -0400 Subject: [PATCH] WIP --- 05-photoresistors/README.md | 26 ++++++++++++++++++++++++++ 05-photoresistors/wot.jpeg | Bin 0 -> 6314 bytes 2 files changed, 26 insertions(+) create mode 100644 05-photoresistors/README.md create mode 100644 05-photoresistors/wot.jpeg diff --git a/05-photoresistors/README.md b/05-photoresistors/README.md new file mode 100644 index 0000000..e1bf596 --- /dev/null +++ b/05-photoresistors/README.md @@ -0,0 +1,26 @@ +# 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. + +
wot
+
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](../04-adc/README.md#measuring-potentiometers), 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. diff --git a/05-photoresistors/wot.jpeg b/05-photoresistors/wot.jpeg new file mode 100644 index 0000000000000000000000000000000000000000..0ece7c4d9cbec7851c63f77c87f8c1a907400900 GIT binary patch literal 6314 zcmY*-2QVDa^Z%WCL^;PHIQ0-j@28($g5XHBL`08zTJ&C{goxfb<&fa?8ieS*M2j9h zK?I5L^Zov3e*gLHo86ta``NcUZ{E(E+1rKNH2_#kO;Zg31OfoSy9Kyi0z?2vh=?K7 z5a@px3Z=bIPY6%18MMSk_IaJV*RH_SP@*zy6)sIoE`|k|363H#pB@<+y*Hbwy5;-k!Xd!pS zWkK^f4;6^vev-kPfeK9$eVX8g`0#5vTD=DS)LVe@EgqV&~UH&nL@-C!FJD2yDP*bz52wt$(*HJJ550!b7>PE-FJ22J9$QFzb-x!_#bkMfO zoEzF};^MK=l|^}m+NhI_iOxTo**rLqA&oe4MfeEMOIM&=tpG|(_=CJlm~CJq2i2L{ zI_4}DR@#OpvZE$&s@+@B{c1foo9GIyUPOcMX)gF|)eke0+tCR!L<CPY8{)!lUf~9Ds`5sp5_ZhReV`iE$6%3OL&z>*3h;Hak@M00? 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