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Old 11-26-2013, 09:20 AM   #15
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Originally Posted by Wayward View Post
...
Parallax sells a 12" submersible strip that converts pressure changes to variable resistance...
Darn, I had seen this before and completely forgot about it. ...too much going on...

Thanks for the point outs. Very helpful.

Z
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Old 11-26-2013, 09:34 AM   #16
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Just thinking out loud here but I would think about mounting this close to the tank on it's own PCB and just run wire to the Arduino.

One thought is to put a tee (3 way) shark bite in the input line to the water pump run a clear plastic water line from the T down into the tank. A small line like the water line in the in a ice maker should not interfere with the pump operation.
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Old 11-26-2013, 09:51 AM   #17
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I'd looked at those level sensors from SparkFun earlier....

The easiest way to plumb one in would be in PVC pipe, with hoses going to the bottom pump suction line and a (small) connection to the tank vent line.
On my 1971 this is not much more that 1/4" tube, but we just want the water level in the sensor to match that in the tank.

In terms of displays a bar graph for the level seems nice... but I really like numbers on things like voltage and current.

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Old 11-26-2013, 11:32 AM   #18
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Quote:
Originally Posted by garry View Post
...
One thought is to put a tee (3 way) shark bite in the input line to the water pump run a clear plastic water line from the T down into the tank. A small line like the water line in the in a ice maker should not interfere with the pump operation.
Sometimes it's not so easy. If you are using air to transmit the pressure from the tank to the sensor, you have to be sure that at zero pressure (tank empty) the line has no water in it and that for at least the height of the tank, the line is pretty much vertical. Any water in the line at zero pressure will subtract from the tank pressure.

It's the principle of the diving bell or putting a glass upside down in water. As the glass is pushed downward, water pressure begins compressing the air and some water begins to creep up the inside of the glass, but the air will be at the pressure of the water at the bottom rim of the glass. But if you have an inch of water in the glass before you push it down, that inch of water pressure is always subtracted from the actual pressure. So you have to have a design that insures that the tubing never has water in it when the tank is empty.

This is not a problem for the sensor that BARTS suggests because he is using the type that is submerged. He maintains the water level even between his external tube and the tank by attaching the tube to the bottom of the tank and to the vent.

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Old 11-26-2013, 12:16 PM   #19
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Could you achieve the vertical intrusion by dropping it down the vent stack? My center bath has vertical stacks on both gray and black tanks... Relatively easy access to both. Just an idea.
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Old 11-26-2013, 06:20 PM   #20
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Originally Posted by Panama Red View Post
Could you achieve the vertical intrusion by dropping it down the vent stack? ...
Exactly, but I'm wondering how you would secure the tube inside the stack. I'm also not too fond of opening the black stack.

Before we all get too wrapped around the axle, this is a great discussion, but the first version of the monitor will use the old probes in the side of the tanks. It will be able to use the early 70s 3/4-wire versions or interpret the 2-wire later 70s version.

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Old 11-29-2013, 06:04 AM   #21
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It looks like all the functions mentioned earlier will fit on a 2.3 by 3.7 pcb. This includes connections to the LCD display, three tank levels, one discrete temperature, battery amps and volts, and multiple digital temp sensors. Note that tank levels are shown on LED ladders.

Z

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Old 12-14-2013, 11:44 AM   #22
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Monitor is up and running. Not finished, by any means, but the basic interfaces and connection to the LCD work. The unit as shown below is 5.5" wide by 2.75" high. The format of the display is totally reconfigurable; current display is battery data on the top line, then two lines of inside and outside temperatures with their min and max, then the bottom line with fresh tank water temperature (in case you want to activate the anti-freeze valve, which is a 1/4" solenoid water valve from the hot water line, about $12 from China) and fridge temperature.

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The tank levels will be shown on three LED ladders ( or two if you have a pre-75 Airstream) to the immediate left of the LCD. The resolution for each temperature display is TBD--there's not much reason to display to hundredths of a degree, except maybe for the fresh tank if you're camping below freezing. It would be nice to accurately estimate the rate of change of water temperature to predict when you might need to do something.

The mechanical mounting, relationship of the Arduino board to the LCD, and some of the small spacing on the Arduino board are not in concrete. Expect some changes in these areas.

If you have input, now's the time to make it.

Once the boards are finalized, they will be available from OSHPARK.com, minimum order of 3 boards in increments of 3, for about $35/three. If you're interested in a single board, let me know now so I can order them when I do the update.

The software is modified C code for the Arduino. You can download the developer environment for free from Arduino IDE. Go to the download tab to get the software. I'll make the basic software available at AirstreamDoctor.com if you want to write your own custom display. If you have the IDE, you can reprogram the Nano board with a USB cable. Dead simple.

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Old 12-14-2013, 09:14 PM   #23
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The LED ladders do the trick (IMHO). I'll get a nice bezel made (laser cut) with holes for the LEDs and labels, plus a place for the water pump switch and I think it will be a complete prototype.

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The LCD limits what can be done, as far as different data. This unit has the capability to read other voltages, other temperatures, but they couldn't all be displayed simultaneously. Maybe multiple display pages are in order (air conditioner in/out temps, two temperatures in the fridge, outside shell temperature (of interest when you're in Mojave in the summer), etc. A push button switch could change pages...

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Old 12-17-2013, 08:12 PM   #24
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Most excellent!
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Old 12-18-2013, 08:12 AM   #25
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Are you sure you don't want to sell them? I for one would be interested. It looks great. Well done.
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Old 12-18-2013, 03:50 PM   #26
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Are you sure you don't want to sell them? I for one would be interested. It looks great. Well done.
Ditto!
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Old 12-18-2013, 07:05 PM   #27
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Quote:
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Are you sure you don't want to sell them? I for one would be interested. It looks great. Well done.
I may go so far as to make up some kit instructions. When I get time to do the bezel you'll see the possibilities, eg, LEDs on the left as shown in the photo, or LEDs above or below the LCD display. Also, need to add a spot for the pump switch.

On another note, I was reading Tim Kendziorski's article (I think it was in the VAC, or maybe the Blue Beret?) on how the fridge works, and realized that if you had some decent temperature readings from the chimney behind the fridge, you could activate a fan or a louver to significantly improve fridge performance. So having an additional page of data (and a switch to get you there) would be very handy.

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Old 12-18-2013, 09:59 PM   #28
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I wonder if a solution to the display issues isn't to use a Raspberry Pi configured as an access point... you can then use any smart phone or tablet as a display device.

I think the Arduino is neat - but pixels count.

- Bart
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