Here's my problem...I need to monitor/track the "health" of a 9V battery (in order to make PWM adjustments as its voltage fades).
The battery is 9V ...not good wrt a PIC IO pin
ok, no problem let's do potential divider...and configure it so the junction voltage equals approximately the PIC's supply voltage - this means when a fresh battery is installed, I'll get the maximum ADC reading, which will get less and less as the battery fades - all is good thus far.
Hmm...but this potential divider is going to eat current all the time ...ok, maybe not a lot, but remember this is a 9V battery...which isn't bestowed with a lot of power delicvery in the first place, so tens of microamps count! Therefore what I need is a potential divider where I can 'lift' up one of the connections at either end of the potential divider (are you following this at the back?!).. but the problem if I lift the ground end of the chain, then the pic ADC pin will float up to 9V - which might not be to good for the PIC IO Pin! (has anyone tested when a PIC faces certain death by pushing the IO pin DC levels?
So to my question...
What's the slickest way of ADC'ing a DC voltage some two to three times higher than the PIC supply itself *but* without incurring constant current draw?
Can any one particular PIC pin withstand much higher voltage (I keep reading about open drain/open collectors wrt PICS...with some implication-rightly or wrongly - that such pins might be able to take higher voltage on the chin?!)
Many thanks,
Hank
Bookmarks