This is a general response to the subject of having a PIC turn itself off after being
started by a momentary button press. (Also, it replaces the original message
which I accidentally deleted.)

Use an optoisolator with a FET output (available from Dig-Key - H11F1 e.g.).
Connect the FET between the chip's Vdd and the battery positive. Connect the
LED to ground and an output pin through a resistor. When the pin is taken high, the supply
latches on. The momentary contact push button switch completes the circuit between
Vdd and the LED through a diode and a second resistor. Pressing the button
turns on the LED and also raises the anode of the diode to Vdd. An input
pin senses the anode voltage and can be used to detect that the button is pressed.
When the button is released, the diode blocks the LED voltage from the input pin. This
leaves the input pin floating, so a pull down resistor to ground is needed.

Press the button once, the PIC powers up, sets the output pin high, and now the
power is on. If the button is pressed again, the input pin is pulled up, signalling the
PIC to do whatever is needed (multiple presses: 1 click, 2 clicks, etc. ?). When
the PIC is done, it lowers the output pin and powers off. The only leakage is through
the FET; if this is excessive, a transistor might be added (the isolation of the coupler
makes this much easier to implement).

John Power

--
http://www.piclist.com#nomail Going offline? Don't AutoReply us!
email listserv@mitvma.mit.edu with SET PICList DIGEST in the body