RCTime with TinyDuino

[acarson]

I'm working on a project for some doctors building an End Tidal CO2 detector which has to be real small. I needed a circuit board with a MCU so I could calculate RCTime and change the ON/OFF status of a Green LED. I noticed something new since the last Time I used TinyDuino in that it now has a battery compartment below the circuit board. (It's been a while since I last designed with it.) So I'm wondering if any of you have worked with RCTime or.. perhaps calculating variant Resistance which can activate an argument when the threshold value is reached. I'm using CaCO3 combined coating heterogeneous Bismuth to calculate changes in the Carbonic Acid on the surface of the inner sensor. The ET CO2 Tube used in intubation has to detect the flow of CO2 to ensure proper insertion of the Trachea rather than slipping esophagus. Once good Trache is found, the CO2 will flow out carrying with it moisture creating Carbonic Acid. I then look at the chemical change in the CaCo3 and Bizmuth surface resistance on the Ambu Bag attachment to activate a Green LED telling the medical personnel they have good Trache. I've accomplished this with a simple Arduino using RCTime but I haven't seen much on RCTime with TinyDuino because the battery needed to calculate the RCTime uses 5V desaturation time to calculate Resistance changes. I have to make this as small as possible.. So is there any of you who might have any experience with Resistance change detection arguments?
This has to be a throw away device.. So expense and size constraints are eminent.  Thanks guys.

[Ben Rose]

Interesting project- Mostly out of my field, but I understand what's needed from the electronics. What sort of resistance range are you measuring? Is it appropriate for a simple voltage divider that's read with an analogRead call?

If you need to stick with measuring the RC time, running from the battery voltage should be something you can account for in the equation if necessary.