Re: [PSUBS-MAILIST] life support method?

[Chris Horne <chris@chrishorne.com>]

OK, after absorbing everything in this thread about life support and doing a
little research out there and feel a bit more aware; I even got the "Life Support
in Small 1ATM Sytems" white paper from Nuytco Research  yesterday.

It seems several things are true:
    - We need a way to "trade off" CO2 that we exhale for O2
    - It needs to be reliable and efficient
    - It could be electronically controlled or manually controlled.
    - Electronic control could measure barometric pressure, which should only
change in an enclosed environment when a person used up O2 and the CO2 was
converted to a solid, or could measure O2 directly in the air by percentage.
    - Manual O2 mechanism would be needed whether a electronic control existed or
not, just in case

So why not just build a system comprised of a embedded controller, an electronic
solenoid or valve made for O2, an O2 sensor, and a CO2 sensor? I'm sure I'm not
the only one on the list that can work with embedded controllers (PIC is what I
had in mind, but something as simple as BASIC Stamp would do the job), O2 sensors
are simply create 0.488mV/percent O2, or around 10.2 millivolts for our
application, so the interface would be no more than a simple A/D conversion, with
possibly an opamp (I'm still checking into the CO2 sensor, but I know it's very
similar). The logic for the controller would be very simple- continuously monitor
the O2 and CO2 and barometric pressure. Constantly allow a small amount of O2
into the air at all times (maybe .2lpm/person, as we consume around .25lpm), and
the controller adds a small amount when the O2 level dips. Monitor CO2 and
barometric pressure simply for reference. Create two of these systems, or imply
interface 2 or more sensors into the same unit.  Ideas? Comments?

-chris