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Forum Index : Microcontroller and PC projects : Water Level with Micromite
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OA47 Guru  Joined: 11/04/2012 Location: AustraliaPosts: 911 |
I wish to use a micromite to measure water level in my tanks (2X poly and 2X concrete)and I vaguely remember a post that mentioned using twisted pair cable as the sensor. Can anyone elaborate on how this process works, was it capacitive? |
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bigmik Guru Joined: 20/06/2011 Location: AustraliaPosts: 2870 |
Hi Graeme, I too am interested in doing something like that.. I have a 2200lt Poly tank about 2.5m high that I would like to monitor.. Mik Mick's uMite Stuff can be found >>> HERE (Kindly hosted by Dontronics) <<< |
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| OA47 Guru Joined: 11/04/2012 Location: AustraliaPosts: 911 |
I did think of using the ultrasonic sender mounted under the top of the tank and the distance function to measure the height of the water but I dont think that the sender would put up with the moisture for very long. This is why I would like to explore the twisted pair as a sensor as it can be completely moisture proof. My first step is to get the micromite to measure the water level and display on a led ladder. The second step is to wirelessly report each tank level back to a display in the house. GM |
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TassyJim Guru Joined: 07/08/2011 Location: AustraliaPosts: 5923 |
I am using some DYP-ME007Y modules for water level sensors in my tanks. They work the same as the HC-SR04 but use a single waterproof transducer with a long lead. They appear to be the same sensors that are used in car parking sensors. I mounted the sensor in a bit of conduit and lots of silicon. A hole in the top of the tank and more silicon finished the job. The electronics are in a box on the side of the tanks and the micromite and RPi are in the pump house. They have been in place for a few months now and give good consistent readings. The only problem I have is with the poly tank. The tank expands in the hot weather and that lifts the sensor up a bit. I wondered why we were using so much water during the day until I sussed that one out. The concrete tank behaves better. Jim VK7JH MMedit MMBasic Help |
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| OA47 Guru Joined: 11/04/2012 Location: AustraliaPosts: 911 |
Jim, do you need a pair of DYP-ME007Y's for each? GM |
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| TassyJim Guru Joined: 07/08/2011 Location: AustraliaPosts: 5923 |
No they come as a control board with the same interface to the MM and a ~2M lead to a single transducer. I have seen ones on ebay with 4 transducers but I kept it simple - one board with a single transducer per tank. This is the test code I used. ' PumpHouse
' Feb 2015 SETPIN 15, CIN SETPIN 16, CIN SETPIN 17, CIN SETPIN 18, CIN SETTICK 299950, doread doread DO k$=INKEY$ IF k$<>"" THEN doKey LOOP END SUB doKey DO k$=INKEY$ LOOP UNTIL k$="" PAUSE 100 Doread END SUB SUB Doread flow1=PIN(15) flow2=PIN(16) flow3=PIN(17) flow4=PIN(18) L1=flow1/330 MOD 1000000' garden L2=flow2/330 MOD 1000000' padock L3=flow3/280 MOD 1000000' bore pump L4=flow4/330 MOD 1000000' house water range1 = DISTANCE(26,25)' house tank vol1 = (227 - range1)*94 PAUSE 100 range2 = DISTANCE(26,24)' garden tank, full = 29.0 vol2 = (260 - range2)*80 PRINT TIME$+","+STR$(range1,4,1," ")+","+STR$(range2,4,1," ")+","+STR$(vol1,6,0," ")+","+STR$(vol2,6,0," ")+","; PRINT STR$(L1,8,0," ")+","+STR$(L2,8,0," ")+","+STR$(L3,8,0," ")+","+STR$(L4,8,0," ") END SUB ' end There are 4 flow meters and two range transducers. With the range, I used a common trigger pin and individual echo pins. That way I saved a few pins and it doesn't matter if all transducers are fired at once, you just read the one you are interested in. They are about $15-20 on ebay. Search for DYP-ME007Y. The minimum distance is 30cm so I had to mount them in the middle of the tank, at the top of the peak. For the flow meters, I tried the ones from Jaycar but they only lasted a few years so I now have some ebay ones. Time will tell how long they last. Jim VK7JH MMedit MMBasic Help |
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| OA47 Guru Joined: 11/04/2012 Location: AustraliaPosts: 911 |
Thanks Jim, I can see the transducers working in the poly tanks but the concrete tanks have flat concrete tops and fill to 100mm of the top. I would like to investigate the twisted pair wire sensor thing as I can see it being easier to implement. I hope someone can steer me in the right direction of this method. GM |
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| MOBI Guru Joined: 02/12/2012 Location: AustraliaPosts: 819 |
Hi Graeme, I think that might have been mine. Originally written for a PIC 675/629. It was capacitive and worked off one pin. The cable wasn't a twisted pair, rather a spiral pair wrapped around a length of conduit to increase the overall length of the cable. The capacitance of the cable varied as the depth of water and consequently, the dielectric constant. The ends of the cable in the water were well insulated. The details are buried in my files somewhere but I'll search a bit more. From memory, the cable (capacitor) connected to an I/o pin and ground. The I/o pin also connected to +5v via a resistor to give an appropriate time constant. The "capacitor" was held at zero by the I/o pin until a "read" was initiated, i.e.,the comparator and the counter was enabled. The result wasn't linear but a bit of a play with the resistor and a lookup table gave acceptable results. I don't know if the uM is fast enough, but I only ran the pic at 4MHz, so.....? David M. |
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| OA47 Guru Joined: 11/04/2012 Location: AustraliaPosts: 911 |
Thanks David, sounds promising. GM |
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| OA47 Guru Joined: 11/04/2012 Location: AustraliaPosts: 911 |
@David, I was wondering if you found any buried in your files. Had a bit of a play today using the figure 8 cable. I can see a change in capacitance as it is immersed in water. I was measuring the change by running the PWM out of one pin and reading across the varying capacitance to a schottky diode and capacitor rectifying the AC signal and fed in an analog pin. Experiments have shown that strangely the lower frequencies have more effect even though the varying capacitance is in the pF range. GM |
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| shoebuckle Senior Member  Joined: 21/01/2012 Location: AustraliaPosts: 189 |
It would be nice to have an in-house display, but if you don't need an at-a-glance display and you have a plastic tank, just use a stud finder. Works a treat (but isn't a nice techie solution). That's what I use. Cheers, Hugh |
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| TassyJim Guru Joined: 07/08/2011 Location: AustraliaPosts: 5923 |
When I tried to use the 'mite for measuring capacitance, I found it easier to use a 555 (or 7555) to give a variable frequency. It works well but is another chip in the mix. Jim VK7JH MMedit MMBasic Help |
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| OA47 Guru Joined: 11/04/2012 Location: AustraliaPosts: 911 |
I am trying the KISS strategy both for reliability and low power requirements. I am about to experiment with different types of twin cable. Maybe larger conductors and thinner insulation might lead to higher capacitance ? GM |
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| TassyJim Guru Joined: 07/08/2011 Location: AustraliaPosts: 5923 |
Thinner insulation should give higher capacitance. Different types of "plastic" will also give different capacitance. I am not sure about the inductance of the twin-lead and how it affects things. I used to twist short lengths of hookup wire to get low value capacitors. I also use short coax as capacitors but that wouldn't suit your water level gauge. For low power, the cmos 7555 is very good. The Maxim ICM7555 datasheet quotes ~100uA at 2V. Jim VK7JH MMedit MMBasic Help |
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| OA47 Guru Joined: 11/04/2012 Location: AustraliaPosts: 911 |
Thankyou Jim for your valued input, I have used the 7555 in projects before as a vf oscillator over radio that were solar powered and required low power consumption but I am challenging myself to accomplish the task with a single chip (Micromite only) GM |
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| Chris Roper Senior Member Joined: 19/05/2015 Location: South AfricaPosts: 280 |
Have you considered using the CTMU. You would probably have to do it as a CFunction but the CTMU is useful for far more than touch, have a look at this APP Note, it may give you some ideas. http://ww1.microchip.com/downloads/en/AppNotes/CTMU%2001375a.pdf Cheers Chris http://caroper.blogspot.com/ |
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| OA47 Guru Joined: 11/04/2012 Location: AustraliaPosts: 911 |
Chris that application note describes some fantastic avenues but alas a Cfunction is currently not my forte.  GM |
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| MOBI Guru Joined: 02/12/2012 Location: AustraliaPosts: 819 |
@GM I found the .ASM file for the PIC based water level sensor but as there was only a few lines, I had commented out the water level bit and used the programme to emulate a windmill controller. The hardware was breadboard and the and the rest bench test proof of concept. The pseudo code: Clear I/o pin to logic zero 'discharge probe capacitance
zero PIC timer start PIC timer set I/o pin to input 'allow probe to commence charge LOOP: if I/o pin = logic 1 then stop PIC timer "the count value is the probe charge time else goto LOOP My aim was to only use 1 PIC and for the probe to be passive. Seeing as I was using 5v circuitry the charge voltage was a bit higher than one would expect of a MM @ 3.3v as a result the count value was greater than the 3.3v version. I don't think using a ticktimer for the counter is valid - suspect the RC time constant is too short for a 1msec tick. Perhaps a software counter i.e count = count + 1 may give some result. I'll see if I can set up a MM test facility and try and do it without external active device such as 555. I've got quite a bit on my plate at the moment. dgm I tested a length of twin flex and got about 22pF per foot. If I wrap a hand around the flex, I get about 5pF extra. Just putting a MM programme together to see what values I get under test conditions. Will try tomorrow. David M. |
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| MMAndy Regular Member  Joined: 16/07/2015 Location: United StatesPosts: 91 |
When all else fails try this ... http://milonetech.com/p/about-etape  |
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| robert.rozee Guru Joined: 31/12/2012 Location: New ZealandPosts: 2294 |
now that does raise an interesting idea: how about a PVC pipe running from near the bottom of the tank to the top, sealed at the top end and open at the bottom. then attach an electronic air pressure sensor to the pipe (somewhere near the top end). when the tank is empty, the pressure sensor will just read normal air pressure, but as the water level in the tank increases the pressure in the pipe will increase in a nice linear fashion. by my reckoning, the pressure increase would be about 100kPa per 10m of water level. to allow for leakage of air, you would need to also have some arrangement that every now and then (perhaps each week) pumped a little more air into the pipe - this could be done with any small air pump on a timer, or even a bike tyre pump that you operated by hand once a week. this occasional air flow would also serve to help ensure the bottom end of the pipe remained clear. cheers, rob :-) |
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