1-Wire Water Level Mesurement

[stevendt]

Hi,

is anyone using 1-wire technology to measure the water level in a pond (with fish) ?

I have seen a couple of ways, one using capacitance and one using IR, both with a DS2423.
Has anyone here tried one or both ?

Regards
Dave

 

[geoff]

I have seen a couple of ways, one using capacitance and one using IR, both with a DS2423.

I havn't built it yet, but this is on my list of projects. I want to measure water depth up to approx 2.5m in a number of water tanks.

There are some ideas on sensor design at http://njhurst.com/electronics/watersensor/ I suspect getting the sensor reliable will be harder than interfacing to 1-wire.

I'm anticipating using something a bit like the 555 circuit in the hobby-boards moisture sensor, except that this time its the capacitor in the RC cct that varies.

Anyway ... if you have success pls post some details ... it's always good to learn from other peoples efforts! Good luck.

 

[Michael McSharry]

I have seen a couple of ways, one using capacitance and one using IR, both with a DS2423.

I havn't built it yet, but this is on my list of projects. I want to measure water depth up to approx 2.5m in a number of water tanks.

There are some ideas on sensor design at http://njhurst.com/electronics/watersensor/ I suspect getting the sensor reliable will be harder than interfacing to 1-wire.

I'm anticipating using something a bit like the 555 circuit in the hobby-boards moisture sensor, except that this time its the capacitor in the RC cct that varies.

Anyway ... if you have success pls post some details ... it's always good to learn from other peoples efforts! Good luck.

 

[Michael McSharry]

The Maxbiotics Ultrasonic Range sensor does a good job of measuring short distances. BSR has a how-to for using it to measure water softner level. It can be interfaced via RS-232 or with something like DS2760/DS2450/DS2438 to do A/D conversion on the 1-wire. They sell in the $25 range. If you are looking for resolutions of under 1" then it will not be a good choice.

 

[geoff]

The Maxbiotics Ultrasonic Range sensor does a good job of measuring short distances. BSR has a how-to for using it to measure water softner level. It can be interfaced via RS-232 or with something like DS2760/DS2450/DS2438 to do A/D conversion on the 1-wire. They sell in the $25 range. If you are looking for resolutions of under 1" then it will not be a good choice.

I decided to give this Maxbotix sensor a try. Some interesting discoveries along the way in case anyone else is interested in experimenting.

I bought the sensor from "Sparkfun", about USD25. I found a really easy way to connect it to 1-Wire was to canibalise a spare hobby-boards solar sensor. I cut off the photodiode to use as a spare, then connected the Maxbotix sensor to the three pin-holes on the board designed for the (non-existent) humidity sensor. Three wires for GND, +5v, and "Analog". It steals power from the regulator on the solar board. That's it ! It works a treat. The VAD field in the DS2438 has a resolution of 10mV which is almost exactly the same as the Maxbotix sensor which reads 9.8mV per inch. I can read distances from 6 inches to 256 inches in 1 inch steps. To check the calibration I connected the Maxbotix serial output to a PC and it came out at 9.7mV per inch, which is only 1% off the supposed specification. Close enough for me, I correct this and convert to mm in software. The Maxbotix sensor itself is amazingly accurate according to my faithful tape-measure.

So far so good. But it can't be that easy ...

Problem 1 is that the Maxbotix sensor is very sensitive to any close up objects interfering with the beam. I had planned to mount the sensor in a PVC tube sticking out the top of the water tank, however the "beam width" is such that the tube would need to be a very large diameter. I ended up with it only 50mm or so above the top of the tank. That wouldn't matter except for a side effect of problem 2 ...

Problem 2 is that the sensor could not cope with the high humidity. I tried all sorts of things but could not find a way to keep the humidity down so in the end a "cheap" sensor had to be replaced with the "expensive" weatherproof version , this time about USD99. Damn! This one does indeed work perfectly in the wet conditions, but has a slightly different range (12-256 inches instead of 6-256). The minimum 12in range is unfortunate because of problem (1). In my case if the tank is full the water comes to 9 inches from the sensor, and I can't easily pull back the sensor because of the beam with issue. Always one for accuracy it annoys the heck out of me that I can't distinguish between "full" (at 9 inches) and "nearly full" (at 12 inches)! Below 12 inches it works perfectly.

So in conclusion, the sensor and solar-board makes an excellent "proximity sensor". I could imagine all sorts of uses but the tank-meter is maybe not the best application. My 1st tank has been working fine for a while now, but I have 3 more to go ... and at $99 a time I'm working on a plan-B based on the capacitance meter for the others. Knowing me it will take a few months, but if I remember I'll report back.

 

[geoff]

The "expensive" weatherproof Maxbotix sensor has now surrendered to the humidity. Curses.

However, plan 'B' based on the capacitance meter seems to be working just fine. I used the concept at http://njhurst.com/electronics/watersensor/. A bit of electronics to convert the capacitance into an analog signal which then feeds the DS2438 on the HB solar board exactly as before. It graphed it out and it's perfectly linear from empty to full and apart from the time to sort out the analog electronics it was cheap to make. This looks like a much better solution than before.