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Thread: Driving ATtiny11 with 9v battery
www.piclist.com/techref/power/batterys.htm?key=battery
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face BY : Mr MCU email (remove spam text)



OK, one last time on this one ... is this a perfect world? ... no, but
for the application it will work very nicely.   Everything is a
compromise.  I don't pretend to be the best engineer, but I am one of
the best designers.

I was incorrect in stating NO power loss, what I should have said is
that the current draw is ABOUT the same on both sides of the zener.
e.g. if the micro is using 1ma (when the LED is off) it will draw APPROX
1ma from the 9V battery.  When the LED is on, (let say you want to use a
cheap one and be somewhat bright so you set it up to draws 6Ma) then 7Ma
(1ma + 6ma) is drawn from the battery.  If you put the micro into sleep,
maybe it draws 100uA or so about from the battery.  Try that with your
shunt regulator!  How much current would the shunt use from the 9V in
all three of these conditions?

I made an assumption as to how the 'product' would work - that is using
a tact switch connected to a port line to turn the unit ON/OFF as well
as work speed and/or brightness - instead of a slide in series with the
9V to simply turn it ON/OFF - not only more function but at a lower
cost.  You could even replace the tact switch with pcb artwork to be
bridged by one's finger ... at NO additional cost - except for a couple
of resistors (for the input spike protection).  Gee, you could go for
broke adding another 'touch switch' or more to do even more functions.

As for voltage regulation, as an LED blinker, there will not be any
significant difference if the micro sees 3.5 volts or 5, other than the
brightness of the LED and possibly the speed of the blinking.  If they
were controlled via the touch switch - no one would notice.

Sure a low Q linear regulator or a switcher would work, but at a much
greater expense and NOT needed for THIS project.  A zener is about
$0.03, 1N400x diode about $0.007, so for less that 4 cents you have an
ALTERNATE low Q supply.  How is the series zener any more 'complicated'
that the shunt?  In your concept, one would save maybe $0.004 (cost
savings of using a resistor instead of the 1N400x) at a cost of MUCH
greater current draw from the 9V.

As far as getting a newbie into trouble, I assume that the kit comes
with instructions AND a description of operation.  If he gets into
trouble, its because the author did a bad job of writing or the newbie
didn't read it!

The ART of design is IDENTIFYING the problem and working out the best
solution, coming in at the lowest possible cost without compromising
function or longevity, and doing so in a unique way.  I have been doing
such for 20+ years with 10's of thousands of products in the field - to
state "bad circuit" pages of "Art of Electronics" - I am afraid that you
know not of where you speak!

Good luck in your endeavors and keep doing things the same old way - its
safer and doesn't require much creativity!

- Mike




David VanHorn wrote:

{Quote hidden}

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