Funny enough, in one of the videos for Experiment 3 I complain about the neighbor's dog barking... and I only just realized as I was wrapping up shooting a few modified versions of the circuit on Page 18 that the dog was barking because of me!
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| Experiment 3 |
If you're wondering if Radio Shack carries a phototransistor, the answer is yes... but don't give up if they don't have it in the slide-out drawer that's got the word "phototransistor" in big bold letters. One of the employees looked in the drawer above that one and lo-and-behold... a single phototransistor for sale. Moral of the story: parts get moved or restocked incorrectly. Look around before giving up.
All the other components I had in my collection, minus a 33K resistor -- I just put two 15Ks in series and was able to get successful results. I did have the 10 microfarad and 0.01 microfarad capacitors but if you don't have these, you'll be happy to know that a VARIETY of values of capacitors will work in this circuit. Just make certain you've got them inserted correctly!
Of course, the first time I turned on the power I didn't get any response. I've learned over time that the first power up rarely works because I always *ALWAYS* wire something up incorrectly... even after I've double-checked against the schematic. I think I may the schematic version of dyslexia because after I get that initial failed power up, I always find the mistake. In this instance, I had pin 8 running to GND, not 5V. Take a look at the schematic and you'll see that Charles' is using the schematic method where a line crossing another line does NOT mean a connection. I saw a connection to GND. A single jumper wire moved to 5V and I was in business.
This phototransistor is very interesting, and I'm glad to see that upcoming experiments will continue to use it for a while. The concept that light (photons) can be used to control the flow of current brings to mind all sorts of fun projects.
I'm including a bunch of videos for Experiment 3 -- the only differences between them are the values of the inserted capacitors. In some instances, you get a high whine... in others a very low ticking sound.
These are always fun little circuits to build because they give you immediate feedback on the special components used (in this case, the phototransistor) and how they behave.
Now, back to that dog. As soon as I turned off the circuit, the dog stopped barking. Turn it on, the dog barks. I hope I wasn't causing him any pain or distress, but I can't stop laughing at how annoyed I was that he kept barking when I was shooting video... my fault, Nixon!
(Got a neighbor with a dog who also likes to play his music really loud? I can see this circuit turned on at 3am in the morning offering a small amount of satisfaction. Just kidding!)
A few odds and ends:
* I'll return to Experiment 2 once my shiny new analog gauges arrive.
* The Mintronics: Survival Pack shown in the video below is $25 (refills are $20). Interestingly enough, it has a 555, a 7805 voltage regulator, and a good mix of useful capacitors, but no 2N2222.
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