[APD] Re: Cheap CO2 controller

[Bill Wichers <billw at waveform_net>]

> I was just wondering, since 90% of recent posts involve CO2 reactors, if 
> anybody has any comments about a eleven-year-old CO2 controller design at 
> <http://www.thekrib.com/Plants/CO2/co2-pvc.html>http://www.thekrib.com/Plants/CO2/co2-pvc.html 
> which, as low pressure solenoids can apparently be very cheap, could be a 
> very economical way of having automatic CO2 injection (I have very soft 
> water and like it that way)?

I wouldn't trust this device. You could use the electronics with a regular 
pH probe though, although you wouldn't have any control over hysteresis. 
You could also use an LM393 instead of an LM339, since the '393 has only 
two comparators instead of the 4 in the '339 and is also a physically 
smaller chip (8 pins instead of 14). With a system like you're talking 
about you would probably only need one comparator -- maybe two if you set 
an on point and a separate off point using a flip-flop. I personally would 
want to have a microcontroller in there somewhere to provide some smarts 
though.

BTW, low-pressure solenoid valves show up rather frequently on Ebay. I got 
some for about $5 each a few months ago.

        -Bill


*****************************
Waveform Technology
UNIX Systems Administrator

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