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'[PIC]: 12V Supply to 16F84A!'
2001\02\06@104110 by Bala Chandar

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My experience may be of interest to most of you.

A few days back, I was testing my code to find the header pulse width,
device code and function code used by a Sony TV remote. After programming
the 16F84A, I inserted the PIC part into the breadboard, switched on the
power supply, pointed the remote at the IR receiver module and pressed a few
keys. I expected to see on the PC monitor the device and function codes
received from the PIC through the serial port. But nothing happened.

I switched off the power supply, checked the code and tried again. This time
again nothing seemed to happen. Then I suddenly noticed that I had connected
the 12 volt supply directly to the positive rail of the breadboard instead
of giving it to the input of 78L05. Immediately I switched off the supply,
removed the F84A and tried to program it. The PIX program reported errors.
But repeatedly pressing the F9 key, more and more locations could be
programmed and finally 100% of the job was completed. After that, I have
programmed the same part a number of times, without any problems. Then I
checked the IR receiver module. It seemed to be working properly.

- Was I extremely lucky not to lose the 16F84A by supplying 12V to it?
- Or is it that the part is protected against momentary supply of voltage
well in excess of 5?
- In the case of the IR receiver module (Vishay TSOP 1738), as per the data
sheet, the supply can be a maximum of 5.5 volts. How did it survive the
overvoltage?

A friend of mine inserted the PIC part upside down. When the circuit didn't
work, he noticed the mistake, removed the power and inserted it the right
way. The circuit worked without any problems!

I would like to hear about similar experiences from others. They will give
us a general idea as to which are the blunders you can get away with and
which are the ones that will blow your chip for sure!

Regards,
Bala

Bombay, India

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2001\02\06@124243 by Olin Lathrop

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> I would like to hear about similar experiences from others. They will give
> us a general idea as to which are the blunders you can get away with and
> which are the ones that will blow your chip for sure!

Getting away with a blunder sometimes is no guarantee of getting away with
it all the time.  You also don't know if your part is now partially damaged
in a way that isn't obvious right now.  Personally, I would toss it in the
trash and get on with life.  How much of your time is $2 part worth?


*****************************************************************
Olin Lathrop, embedded systems consultant in Devens Massachusetts
(978) 772-3129, spam_OUTolinTakeThisOuTspamembedinc.com, http://www.embedinc.com

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2001\02\07@051444 by Vasile Surducan

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On Tue, 6 Feb 2001, Olin Lathrop wrote:

> > I would like to hear about similar experiences from others. They will give
> > us a general idea as to which are the blunders you can get away with and
> > which are the ones that will blow your chip for sure!
>
> Getting away with a blunder sometimes is no guarantee of getting away with
> it all the time.  You also don't know if your part is now partially damaged
> in a way that isn't obvious right now.  Personally, I would toss it in the
> trash and get on with life.  How much of your time is $2 part worth?
>
 You forget one thing : not every one of us are living in US.
Stories of Microchip they have selling offices world wide are just
stories...sometime you can't find at all a Microchip microcontroller...
Vasile

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