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Author Topic: Warning! One Million Ohms  (Read 6545 times)
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Grand Blanc, MI, USA
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I shared this little project with a few folks here on the forum and got good feedback and suggestions that I could sell it. So I thought it'd be fun to try. It's listed on tINDIE.com for anyone that's interested. Guaranteed to keep the zombies away from your workbench!

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MCP79411/12 RTC ... "One Million Ohms" ATtiny kit ... available at http://www.tindie.com/stores/JChristensen/

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I don't think you connected the grounds, Dave.
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That's an awfully (physically) large resistor!
Isn't there an exercise question in Horowitz and Hill that says something like "Why will you never practically exceed the rating of a 1/4 watt 1Mohm resistor?"  ?
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Grand Blanc, MI, USA
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That's an awfully (physically) large resistor!
Isn't there an exercise question in Horowitz and Hill that says something like "Why will you never practically exceed the rating of a 1/4 watt 1Mohm resistor?"  ?

LOL, it's an especially large resistor considering it's not actually part of the circuit. It's a 2W unit, so something like 1400V would be needed to generate dissipate that much power.
« Last Edit: September 04, 2012, 08:44:39 am by Jack Christensen » Logged

MCP79411/12 RTC ... "One Million Ohms" ATtiny kit ... available at http://www.tindie.com/stores/JChristensen/

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Jack, you gotta share the story behind this.
I don't think I can type it up well, and can't find a link for it.
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20 LEDs are enough
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One Million Ohms is for wimps: http://www.silverlight.ch/resistors.php smiley-wink
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Jack, you gotta share the story behind this.
I don't think I can type it up well, and can't find a link for it.

Evidently the joke goes back quite a ways. Engineers and other techie types would tape a 1M resistor to a piece of paper and write, "Warning! One Million Ohms", then post it on the lab door, etc. In some cases this was successfully used to keep the janitorial staff or others that didn't "get it" from messing with a project.

The incredible thing is that even at my advanced age smiley-wink somehow I had never managed to run across the joke until last year, when Grumpy Mike mentioned it here on the forum. I had a good laugh, and knew right then that there had to be an electronic version of it. I'm hoping others will want one, too. I gave some out last Christmas to friends and co-workers, at least one of which was questioned about the danger of having it on his desk at work!

Not long after I had the first boards made, the joke turned up as a question in my son's physics textbook, with the query, "Why do physicists and engineers find this amusing?" smiley-grin
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This makes me wonder when dihydrogen monoxide (DHMO) will make it into the textbooks smiley-wink
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Why all the components on the bottom...smoke and mirrors?
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It is an attiny that is intended to provide the "action".
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Why all the components on the bottom...smoke and mirrors?

The 1M resistor is smoke & mirrors, everything else is part of the circuit. Four dropping resistors for the LEDs, a power supply bypass capacitor, a button to change the flashing speed & pattern. And an ATtiny85.
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MCP79411/12 RTC ... "One Million Ohms" ATtiny kit ... available at http://www.tindie.com/stores/JChristensen/

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Of course! IT BLINKS! Now all you got to do is add an IR sensor and a audio module that cry's DANGER! DANGER! when someone gets to close.
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Whenever I encounter resistances of one million Ohms or more, I just use my DMM as a shield.  It can measure several million Ohms, so I know I'm safe behind it. smiley-wink
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Of course! IT BLINKS! Now all you got to do is add an IR sensor and a audio module that cry's DANGER! DANGER! when someone gets to close.

Ha! Interesting idea! Someone also suggested having it turn itself on at random intervals. That might raise some eyebrows. I might have to work on alternate firmware at some point.
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I've never heard of this joke before but as soon as I saw the board I laughed and laughed, it's hilarious.
As an "oldie" I feel an microcontroller is a little bit overkill for the flashing though as a good ol' 555 would've done just fine. in fact with a few added components and a 556 it should be quite possible to get some cute random actions into the circuit while getting the impressionfactor up a bit.
 smiley-mr-green
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I've never heard of this joke before but as soon as I saw the board I laughed and laughed, it's hilarious.
As an "oldie" I feel an microcontroller is a little bit overkill for the flashing though as a good ol' 555 would've done just fine. in fact with a few added components and a 556 it should be quite possible to get some cute random actions into the circuit while getting the impressionfactor up a bit.
 smiley-mr-green

I certainly am glad I'm not the only one that hadn't heard it before! smiley-grin  From a purely economic standpoint, the ATtiny85 makes sense. Advantages are individual control of the LEDs (several flashing patterns and speeds), no additional timing components, no power switch, automatic shut off (sleep mode) and re-programmability. But I know what you mean, certainly this circuit does not take advantage of much of the MCU's capability.

I have a lot of computer-literate friends that don't really know microcontrollers or much about electronics, and I like to explain to them that the thing is a complete computer, is handling 1000 interrupts/sec, has three kinds of memory, an ADC, can run 10 MIPS, costs $2, etc.
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MCP79411/12 RTC ... "One Million Ohms" ATtiny kit ... available at http://www.tindie.com/stores/JChristensen/

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