RE: [PSUBS-MAILIST] Life Support Revisited/CO2 monitor

[William Alford <walford@dbtech.net>]

At 02:11 PM 8/6/2003 -0400, Alec Smyth wrote:

>when I read the manual I was left wondering about the interface protocol. Did
it by any chance come with
>more detailed instructions than what is in the 4 page online manual?

same as the pdf on the web. 

>>From reading that, it isn't obvious to me how I would tell it to take a
>reading, or where I would measure the output.

see illustration of the board on page 4 for the "analog output connector" shown
on the board. It outputs a linear voltage between those two pins of between 0.1
- 2.6 v as concentration varies from 0 - 2500 ppm CO2. The digital interface
connector is also shown on the board diagram and has pin descriptions for
connectivity in the chart on the page below it You would have to interface it
with a digital readout to measure the analog voltage. Perhaps one like this--
 http://www.e-sci.com/circuitT/RENDER/0001/C5/C5_200/10616.html.  sells a
digital panel voltmeter, the DMD-3500B. It's external dimensions are of
3.090"x1.675" and it is made to fit a cut-out hole of about 3.050"x1.575" and
very reasonable at $20. However, one option for the CO2 meter is an LED meter
attachment.


> Are you planning on interfacing this to something else, or were you going to
use the optional readout?

both. I did order one with the optional LCD readout and intended to take the
analog voltage output and use with a simple voltage comparator to trigger an
alarm/action for any preset level that I select. Perhaps several with different
tones for various danger/interest levels as well as different colors of LEDs
for various caution levels. One will likely be a relay connection for
activating an offboard circuit or switch. I've been bogged down with other
issues and have had it on the shelf for over 6 months without time to fool with
it. It's a really cool little unit, but note if you order one that there are
TWO versions. One has the sensor opening to read the surrounding atmosphere and
the other has two little ports (shown in the photo) for gas to pass through
under pressure. I chose the ported option since I'm measuring a pressurized
tank and not using this particular one in a submarine at this time, but the
functionality should be the same. When I lay out a printed ckt board for the
accompanying comparator/etc for it to all fit on, I'll post back to the list in
case anyone is interested.

>http://www.dcs-inc.net/m305.htm, around $165 I think.

William Alford