Reading Outputs as Inputs
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Dan Michaels wrote:
I agree Dan, the bulk of my practical experience is from
repairing things, although I have done a lot of design
over the years. The things I have to repair are always
due to engineers pushing the spec. Like using a 5amp
transistor to switch 5amps.
So if your little car has 150hp you are going to drive
everywhere with the motor screaming at peak hp at
redline towing a big caravan?? How long would it last?
About as long as your new Taiwanese VCR power supply does.
After my initial trade as an industrial electrician
I did a couple of years of industrial electronics,
a very practical training mainly about microprocessors
and how to interface them with everything from special
sensors to huge motors. We were taught that good
design over-rates parts at 10x. So you use a 10w
resistor if it is known to dissipate 1w. This gives
a long term reliability guaranteed to work 24 hours
7 days, even in a hot environment.
So anything less is simply trading reliability for
cost, if you don't care that a large percentage
of your product will fail within a couple of years
that's fine. Some poor sucker like me will end up
being paid to fix it, or should I say improve it,
because I will be putting a decent sized transistor
in it. ;o)
Back on topic, I feel uneasy driving a PIC pin
more than 10mA, I prefer about 5mA if I can.
I don't want it to fail in two years. Driving it
into a short gives me the heebie jeebies. How
much does a resistor cost? 1 cent?
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