I am currently doing my first project where current consumption is an
issue.  I've configured a keypad on portB of a 16F628 and have my program
set up so that I'm using the internal port B pullups.  I have the PIC sleep
except when a key is pressed.  The program works great.   However, I am a
little concerned by the current consumption.  In measuring the current
drawn by the circuit I'm getting 85 microamps.  I've checked my meter by
measuring the current consumed by a circuit that simply has a 1 megaohm
resistor in it, and I get the expected 5 microamps.

That's pretty good, but Microchip seems to indicate the current consumption
of this device during sleep should be much lower.  So I set up a simpler
circuit that has only a PIC, all pins configured as outputs and all pins
tied to ground.  I still get about 85 microamps.  I tried it with all pins
configured as inputs.  Still 85 microamps.

Then I read application note AN606, where it talks about a circuit that
measures current consumption of the PIC by putting 100 ohm resistors on the
input and output and alternately shorting them and measuring the current
differential.  This would seem to imply that there is something wrong with
my technique of simply using a multimeter to measure the current
consumption of the device.

As I said, I'm pretty new to very low power circuits.  Is my device
actually consuming 85 microamps, or is there something wrong with my
measurement technique?

Thanks,

John Hansen

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