Anyone have any good ideas for a low battery detector NO A/D

[William At MyBlueRoom]

Looking for a simple detector that only uses 1 I/O pin on a PIC.

There are a few chips from maxim but I'd like to find something easy to source and simple and very low current draw.

2.7 - 3V DC would be nice... A zener & transistor?

 

[Russlk]

I am just learning how to program a PIC myself, but what I would do is put a voltage divider on a logic input. The input will be high until the battery drops to the point that the divider output is at the switching point. The input will be noisy at that point, so depending on what you want to do, you may need to lock the input out once it has gone low.

 

[akg]

like russlk suggested using a voltage divider , and o/p of that given to the external INT pin , which has schmitt trigger i/p, or connecting them to internal comparators.

 

[William At MyBlueRoom]

Problem with simple voltage divider

I'm not using a regulator in the design (See the Armadillo on my site) **broken link removed**

And I want it to trip at about 4 volts, plus very high impedance so as to impact the battery as little as possible.

 

[Russlk]

The 16F628A has two internal comparators and a programmable voltage reference, so you have all the parts needed to make a very accurate low voltage detector, read the data sheet.

 

[Nigel Goodwin]

Re: Problem with simple voltage divider

And I want it to trip at about 4 volts, plus very high impedance so as to impact the battery as little as possible.

I've not looked at the circuit, but 'very high resistance' (NOT impedance!) is only of value if the total current consumption is already extremely low. There's not a lot of point saving 5uA if the project already takes 100mA.

As already suggested, use a PIC comparator - available in many of the newer PIC's.

 

[JohnBrown]

Hmmmmm. I'm not so sure about this - I think you can use the term "impedance" when discussing DC, although it is exactly equal to resistance.
That's not to suggest that the two terms are interchangeable, obviously.