Scott wrote: > I use OWFS to monitor various parameters of my saltwater aquarium. One > of the biggest things I'd like to monitor is the approximate height of > the water in my sump to know when additional water needs to be added, > etc. It also gets a little bit interesting because I have baffles in > my sump and filter floss between them to filter particulate matter as it > goes through the baffles. As the filter floss gets plugged with debris, > it restricts the water flow creating a difference in heights on each > side of the baffle. I can't just monitor one side or the other and > assume the water level because the two levels may be identical (zero > restriction with newly replaced filter) or up to ~8 inches different > (plugged filter in desperate need of replacement). I need to know the > level on both sides and average it to get a true standard volume baseline. > > I've thought about using an array of float switches and a GPIO chip to > monitor which switches are open/closed to deduce the water level, but > there's several reasons why I haven't gone that route: reliability, > space, and resolution to name a few. The other day I came up with an > alternative - use an array of temp sensors to monitor the differential > temperature between the air and water to approximate the water level. I > already track both those temps, giving me a sort of calibration standard > for comparison. As long as the temp sensors are spaced at a known > distance, and the starting height is known, I just write a script to > read and compare all the temps. The water height should be between the > two adjacent sensors with temps matching the known air/water temps. The > resolution of the array would be determined by the distance between and > number of temp sensors in it. > > I'm I computer guy, but definitely no EE so I thought I'd bounce this > design off the list to see if there's anything I should add to the > circuits I'm not thinking of. I'd probably (since I already have a slew > of them) use DS18B20 chips all wired in parallel with a network branch > (DS2409) to separate the two sides and logically segregate the arrays > from the general temp probe population. Each array of temp probes would > be wired up and then completely encased in epoxy to protect it from the > water. I've already done this with TO-92 form factor temp sensors and > it works quite well. > > Here's a diagram I put together with my design. Let me know if anyone > has thoughts, etc on it: > > Just one thought... how much airflow do you get in the filter? How closed is it? You may have air temp very close to the water temp if you have 'still air'. It may be so close that the temps will appear the same, or within a margin of error that makes them that way.
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