I've just designed a plain vanilla 12-bit A/D conversion board using a
16F84A.  The PIC controls the A/D conversion speed and sends data to the
serial port of a PC at 9600 baud.  On the PC side, QBasic reads the serial
port and deals with the data.  The board is powered by its own 9-volt
battery.  To complete the design, I would like to be able to turn the power
to the board on and off using one of the serial control lines.  Since it is
battery powered, the circuit needs to present a minimal drain to the battery
when the board is off.  Could someone suggest an easy circuit for doing
this?  Low parts count would be nice.

Thanks in advance.

Michael O'Bannon, Ph.D.
Atlanta, Georgia