Howdy,
I know this is off topic, I'm not sure how
tolerant this list is to a few
off topic posts so please
accept my apologies in advance if this is
too far off from PICs for your sensibilities. I'll try to keep it brief.
As usual, replies can be directly to me to avoid cluttering
the list.
I play with modifying TI calculators in my spare
time, one modification
requires a switch.
Instead of using a physical switch I want to control
it with a circuit that senses if the calculator is on or off
and switches
the device appropriately. I have a point on the calc
that is 5v when the
calc is off, 0v or 2.5v when it is on (depending on screen
contrast).
I want the power to the device to be off when the voltage at
this point
is above about 4v (actually Vcc, it varies).
I am currently using a circuit I designed with some junk box
transistors,
however, not having any formal training, I haven't done it
optimally, and
it is quite sensitive to variations in component values (about
10% of my
transistors work in this design). Also, the transistors
drop too much
voltage, the power to my device (an inverter) is less than
what it could
be. Therefore, I would like to redesign the circuit to
use a MOSFET
or something similar that has very low on resistance.
However, not
having used them before, I have no idea how to proceed.
As usual
with electronics, there is no 'How to use a XXXXX' to be
found, or even
a 'How NOT to use a XXXXX'.
Details for the device can be found at my web
page:
Thanks in advance if you can help me
out.
DK
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