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I'm doing a simple children's workshop in which they will build a small musical instrument on a breadboard with an attiny13a, ldr and a led. Right now it's powered by a 9v block and a regulator. Through some of the uncarefulness of the children, I discovered that the attiny13a seems to run just fine on 9v and the sound output is even louder! The regulator on the other hand gets hot, burning some children's fingers and is easily broken when the children wire it up incorrectly.

I've been running a test of skipping the regulator and running the 9v directly into the attiny13a. This has been running for more then an hour without problem, it doesn't get warm at all, though the clock speed might have changed a bit, which is no problem for my purpose. As long as the chip keeps running for the duration of the workshop (an hour) plus some more. Even though it seems practical to just run on 9v, the attiny13a -is- only rated for up to 5.5v. What could be some unexpected side effects?

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  • \$\begingroup\$ The fact that it's running on 9V now is pure luck. Run that same test 100+ times with 100+ different micros and batteries and see what happens. Spoiler: nothing good. That 5.5V absolute maximum is an absolute maximum for a reason. \$\endgroup\$
    – Matt Young
    Apr 6 '16 at 13:00
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    \$\begingroup\$ Why use 9V? 4XAA cells in a battery holder and an in line diode on board give just the correct voltage with polarity protection.. \$\endgroup\$ Apr 6 '16 at 13:07
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    \$\begingroup\$ You're not going to set a good example for the kids by powering <5.5V rated electronics with 9V (: \$\endgroup\$
    – Paul
    Apr 6 '16 at 13:16
  • \$\begingroup\$ Why does the regulator get hot? How much current are you pulling? Note that the attiny13a is only rated to sink/source 40mA per I/O pin, and 200mA total. If the regulator (which only has to drop 4V) gets hot, you may well be exceeding that. \$\endgroup\$
    – marcelm
    Apr 6 '16 at 13:48
  • \$\begingroup\$ The regulators are getting hot even without a load. So my guess is that I bought them just a little bit too cheap. \$\endgroup\$ Apr 11 '16 at 13:08
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What could be some unexpected side effects?

A shorter lifetime of the microControllers. Their maximum operating voltage is 6 V, with 9 V you're above that with a significant margin. Although the chips work now you are stressing them. So don't be surprised when they fail. That can be in a minute or in a year or maybe in 10 years. That is almost impossible to predict.

The normal manufacturer guaranteed lifetime of a chip operating at maximum ratings is usually 10 years. Outside maximum ratings it's anyone's guess.

It could well be that the chips still work long enough to suit your needs at 9 V. But no guarantees so I would keep spare ones ready.

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I could just refer you to this answer of mine which relates to overclocking, but also covers supply voltage. But reuse of the image makes it (arguably) worth adding this answer.

Do also refer to the answer linked to above !!! :-) .

Manufacturers provide specification sheets which indicate voltage ranges which a processor will work within, and "absolute maximum" voltage ranges over which the processor may not work correctly but will not suffer permanent damage. Applying voltages outside the "absolute maximum" range means that you risk doing permanent damage to the device. TYhe image below summaries what you can expect from your processor under various conditions of clock speed and voltage. The actual values are for an ATMega128 and may need to be adjusted for your device, but, the principle is the same - if you don't want to play hard ball with Dirty Harry, stay inside the Safe Operating Area. Anything to the right of this may be fatally fatal. Any other non-grey areas have expectations as labelled.

enter image description here

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Why use a 9V battery and regulator? 9V batteries are expensive, and you need a regulator that wastes most of the power you can get out of them.

The attiny13a runs on anything from 1.8V upto 5.5V.
So, use two AA batteries in series for 3V.
Cheaper, runs longer, won't get hot, won't go "pop."

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  • \$\begingroup\$ I will do this for a next iteration. Now, it was simply a matter of economics and performance. A 9v clip and regulator is a lot cheaper than a 3 or 4 AA battery holder. Also the output of the speaker is too weak at 3V. For the next iteration I will make some tests with a transistor to see if I can make the output louder even on low voltage. \$\endgroup\$ Apr 11 '16 at 13:10
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The worst I've seen, is a little click, the distinctive "burning transistors" smell and a little plastic piece of casing flying across the table, following Murphy's law, in the eye of the child with the overprotective lawyer parents.

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