January 17, 2011
I have the following problem.
I’m rebuilding my SEA RENDERING http://letsmakerobots.com/node/21098 project from two Arduinos to one FEZ Panda running .NET
In my original setup I had one switch for the main power and one for stopping the logging. The reason for this is that if one shuts down power when the system is writing to the SD card, you might end up with a corrupt log file or in the worst case a completely ruined SD card. In an attempt to remedy this I made the following circuit that worked great on the breadboard.
The thought behind the circuit is that when the 12V is removed the voltage regulator goes down giving me an interrupt on pin 5. The system flushes all data to SD and unmount it. The charge in the 4700uF capacitor gave me enough time to do that.
According to Murphy’s law “If a prototype functions perfectly, subsequent production units will malfunction.“ and that kicks in here.
The problem (I think) is that the prototyping was done on a micro SD with nothing else attached. In my boat I have a normal size SD and GPS, digital compass etc. attached. So it drains the capacitor to fast.
So this I what I want to do.
When the main switch is turned off the volt regulator gives me a signal. Then I would like to pull a 9V battery online and keep it supplying power until I pull a digital pin low and turn everything off.
So, the great minds of LMR, -is this possible? I think resorting to a relay will drain the capacitor to fast so there must be some other way.