Forum: Analog Circuits Raspberry Pi PIR motion sensor power supply with Schmitt Trigger

 Author: Axel M. (aaameyer) Posted on: 2014-03-06 16:23

Rate this post
 0 ▲ useful ▼ not useful
Hello,
I’m trying to develop a power supply for my Raspberry Pi which is being
switched on by a PIR motion sensor and then the power shall remain on
until the operating system has shutdown. The power will be supplied by a
12V battery therefore power consumption of the whole system is
important. My Raspberry Pi is modified to run with direct 3.3volts like
described in http://www.daveakerman.com/?page_id=1294
When the motion sensor detects a movement the unit shall start (until
the boot process the GPIO pin has ~1 volt). After the system starts I’ll
set GPIO4 to high (3.3 volt). A Schmitt trigger shall supply the power
until the operating system has shutdown which is being indicated that
the GPIO4 is set to 0 volts.
From my research in the internet I think that a Schmitt trigger like the
HCF4093B could be used for the power hysteresis and a switching
regulator like the LM2596 is the most efficient way to drive the board.
But I’m not that familiar with electronic designs, so I have some
questions:
-Would the system work in general like this?
-I have read that the Schmitt trigger requires some capacity. If so how
can I calculate the capacity which is required and where to connect it?
-As I understood the Schmitt trigger works as comparator. Where do I get
the voltage to compare with? If I would use here a linear voltage
regulator it is not efficient anymore!?
I would appreciate your comment and help on this problem.
Axel

• $formula (LaTeX syntax)$