Need On or Off logic level from a .30v to 5.0v input without affecting the signal

[iso9001]

So.... I have a project where I have a 0.3v to 5v signal (output of a resistor ladder switch) that I need to use as a wake interrupt for a pic (INT0/1).

I'm have a few options on how to do this... buffer the signal, hook it to a mosfet, diode, etc. But, I'm having trouble figuring out a "right" way to do it.

The trouble is, it may occasionally be below the logic of the pic (it'll read it as 0 anywhere below 2v) AND I absolutely can not effect the voltage at all (on the rest of it's circuit). I can sample but that's it. One other consideration is that I would really like to keep the entire circuit as low current as possible in while in sleep mode. Which means if I have to run the 5v regulator and a buffer circuit for this wire it's probably not worth it. However, if I could directly hook this circuit to the regulator so that whenever not zero volts was on that line it would trigger my regulator to be on that would be swell.

Any suggestions? Thanks!

 

[blueroomelectronics]

Many PICs have a built in comparator (with interrupt too!), just set the - input to 0.3V and it'll trigger whenever the + pin goes above or below 0.3V

 

[iso9001]

Hmmmm... I think I may have forgotten that the pic's comparator might go that low. I would have considered a real comparator but that would have required the regulator and comparator to be on all the time, so does this I guess.

I'll keep searching.

 

[blueroomelectronics]

Yep they go that low, they're analog devices. Yes you require power but I do believe you can sleep the PIC and it's one of the wakeup sources.

What's the power source?

 

[iso9001]

12V battery to a 5V regulator. The lower the Iq I can get the better.

I'm trying to think if it would be worth looking into a comparator that directly turns on the regulator. So the chip doesn't deal with sleep at all, it just shares a an OR gate with the comparator so that once the regulator is ticked on I can keep it there even if that external signal dies out.