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Electronics Puzzler by Mr. Forrest M. Mims III himself ! Answered

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Below is a link to Jameco's latest Forrest M. Mims III electronic's puzzler: can anyone figure it out without cheating? The link provides more detail. plus some hints....

JAMECO PUZZLER 2 - What's the Missing Component?

26 Replies

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Goodhart (author)2009-05-24

Would you believe it is JUST an LED ? A clear cased RED LED. That's all folks ! LOL

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lemonie (author)Goodhart2009-05-24

Yes, that's what I thought see below

L

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Goodhart (author)lemonie2009-05-24

The red LED is being used as a sensor in this case. The clearer the case it is in, the more sensitive it is. I had always known that LED's and other clear cased diodes reacted somewhat to light, but I never did much experimenting with it.....I am going to do some now though...

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dombeef (author)2009-05-18
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Goodhart (author)dombeef2009-05-18

Ok, if you look at the answer (at the site ) you'll be surprised :-)

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Goodhart (author)Spaceman Spiff2009-05-10

That would be seen as a resistor and probably would not work ;-p

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fwjs28 (author)2009-04-28

o, oh my....well, it has a graph i assume thats what it is that has volts to light....so my guess is an LED or light bulb circuit?

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Goodhart (author)fwjs282009-04-28

the missing component, is to detect certain wavelengths of light....

one of the hints states: The missing component is clearly some kind of photodiode or photoresistor. But what kind?

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fwjs28 (author)Goodhart2009-04-29
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Goodhart (author)fwjs282009-04-29

Did you go to the site and read the article? It says it will pick up certain reds, but not the near IR of a remote control.

It isn't what most would consider a normal detector but they do react to light in their wavelengths....

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user
Goodhart (author)whatsisface2009-04-28

one doesn't think of one of these as a detector normally ;-)

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user

is it a green LED? of to check

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whatsisface (author)Goodhart2009-04-28

Really? It's what we used in our school projects, with a pretty much identical circuit.

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Gjdj3 (author)2009-04-28

I know I'm going to just kick myself once I look up the answer.

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Gjdj3 (author)Gjdj32009-04-28
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Gjdj3 (author)Gjdj32009-04-28

I can't believe I didn't figure that out. Haha, I must have been overthinking it.

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Goodhart (author)2009-04-28

I had seen something similar to this YEARS ago (maybe even submitted by Mr Mims), and I had forgotten about this particular "ability" of this component :-)

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NachoMahma (author)2009-04-28

. Woot! . If it had been asked as a "I found this PCB and can't figure out what '?' is" question, I never would have figured it out. Since it was a puzzle, it started thinking "backwards." It's a common part - if it had been more "esoteric" I wouldn't have gotten it. . But in the end, it was just a lucky guess. ;)

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lemonie (author)2009-04-28

The right hand arrow isn't labeled, but at a guess the missing piece creates the LIGHT output represented in the I-doubt-it's-actually-that-linear-graph?
(e.g. a bulb / LED)

L

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Tool Using Animal (author)2009-04-28

It's a puzzle piece with a ? on it.

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Lithium Rain (author)2009-04-28

/facepalm It was so obvious once I looked up the answer...

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