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Old 03-01-2015, 02:25 PM   #41
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Also, you might be interested in this Arduino bare-bones kit. It has an ATMega chip with Arduino bootloader installed, as well as enough parts to make a home-brew arduino board. It is the UNO version of the Arduino, but allows you to custom make an arduino application without having to mess with the Arduino circuit board:

I have used these in the past, and all you need is a USB/serial board that you can get at SparkFun to connect the system to the Ardunio programmer.

BB-ARDUINO: JAMECO KITPRO: Education & Hobby Kits
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Old 03-01-2015, 02:46 PM   #42
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I located the RF tx/rx modules I used. I bought about half-dozen of them for around $5 per pair:



For that price, it's not worth engineering and building your own. They are 4 channel and each receiver channel is more or less TTL logic, and tracks the 4 channel state on the transmitter.

The TX module is on the left, and of course, you would extend the coiled up wire for the antenna. They operate in the 455mhz band, and have a 100~200ft range.

I was using these to do remote camera and flash unit control, in situations where I did not want to have to use an arduino board for each camera.

I can't find them on eBay anymore though. The TX part number is: TM1000-4 and the RX is RM4SGM. These are generic made-in-China stuff.

eBay does have a lot of similar tx/rx modules but are single channel encoded with a digital signal. This would require both tx and rx module to be interfaced to an arduino board to decode the transmit signal. It is doable, but a bit more involved is all.
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Old 03-01-2015, 03:25 PM   #43
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That chip is bigger than the Arduino board I'm using! The Arduino Mini is extremely small.
Even those RF modules are bigger than the Arduino board I'm using.

You can't really tell from pictures but this guy is tiny (approximately 1" x 0.5").

Thanks to your suggestions that had me digging through the ATMega328's datasheet I've fixed the power up issue I was having (It wouldn't accurately read the "cap" value of the tank on a power up without me disconnecting and reconnecting the wires--The 328 was doing something to the logic pin messing with the readings).

The fix is the fact that the 328 (and I presume other variants of the ATMega) has an analog comparator built in. Thus instead of watching a digital I/O pin to go high (which means the voltage is above 2.5V or so) I can set my threshold voltage and have the 328 watch for that (in this case its 4.5 volts: a 1k/10k voltage divider providing the reference).
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Old 03-01-2015, 07:21 PM   #44
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Of course you can buy the ATMega328 chip used in the uno in a surface mount version, but then you would have to burn your own bootloader. Its the same chip used for the mini.

The Jameco bare bones one I showed is popular for many hobbyists that as it is a DIP rather than surface mount.

One thing I am curious about. The boot up delay for the ATMega328 can vary depending on the amount of code that is loaded. In my camera controller project, it takes a couple of seconds to boot. However, I am using almost 30k of code - including several libraries (LCD, EEPROM, etc), and I would suspect your project will boot much faster due to presumably less code.

Have you tested the on-time delay from depressing the switch to measure the tank level until actual display? If the boot time is more than a second, it would be a bit annoying I think.

Anyway, thanks for starting this project. I have not messed with any Arduino technology for a couple of years, and I have hundreds of dollars worth of parts in my parts box, so it'd be fun to build something again.
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Old 03-01-2015, 07:28 PM   #45
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If you are into Arduino, you are probably aware of a couple of good parts sites; Adafruit Industries, Unique & fun DIY electronics and kits and www.sparkfun.com. If you are not aware of them, they have tons of goodies.
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Old 03-01-2015, 07:47 PM   #46
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A simple alternative to a remote indicator would be to attach an electronic buzzer (which you could turn on and off) that would sound when the tank is full, empty, etc. so that when you are outside filling the tank, you should be able to hear the buzzer go off when the tank is full.

It would be a lot easier than wireless annunciation.

One word of warning though. I have been accused of adding circuitry to a project just because I might have a left-over gate or function. I am guilty as charged in that regard. But I figure if you are paying for a quad op-amp, you should use all of them for something.
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Old 03-01-2015, 08:00 PM   #47
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I also ran across a product that Molex demo'ed a couple of years ago - a capacitive external tank sensor, but have not found any info on availability.

Capacitive Fluid Level Sensors - Molex
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Old 03-01-2015, 09:00 PM   #48
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Quote:
Originally Posted by FW28z
One word of warning though. I have been accused of adding circuitry to a project just because I might have a left-over gate or function. I am guilty as charged in that regard. But I figure if you are paying for a quad op-amp, you should use all of them for something.
LOL! I hear ya!

The image size is about 3k and so far it looks to be about 1 second bootup time, plus the time to make the measurement. I figure I'll flash all of the LED's on the panel as soon as it starts then take the measurement then show the result.

Quote:
If you are into Arduino, you are probably aware of a couple of good parts sites...
Actually this is the first time I've used an Arduino. In the past I've gone with pure assembly running on a microcontroller but I have to admit that using an Arduino is far easier than handling everything yourself. It really is a nice package to get something up and running quickly. (The boards I purchased came from sparkfun.com.)

For this project, since it really is a one-off, I'll just solder the circuit up on a perf-board (like these: http://www.amazon.com/Vktech-10pcs-C...VMV2J9HEQP7ER8 ). The Arduino board will sit on top. Then I'll seal it up in a box and mount it to the Axis in front of the black tank--fortunately there is a junction box not too far away where I can pull the house 12V from (including a block of fuses).
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Old 03-01-2015, 10:28 PM   #49
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Are you using the Capacitive Sensitive Library?

http://playground.arduino.cc/Main/Ca...=Main.CapSense
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Old 03-01-2015, 10:38 PM   #50
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I started with that but then once I discovered the comparator (which that library doesn't use) I stopped using it. Using the comparator gives you a much more accurate reading (since you can time the charge up/down to a higher and lower voltage).
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Old 03-01-2015, 11:12 PM   #51
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Any issues with sensitivity vs. wire distance from the sensor to the Arduino pin? Or are you mounting the Arduino adjacent to the foil?
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Old 03-02-2015, 12:17 AM   #52
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The capacitance of the tank is really low and thus I've been using a 10M resistor to make the charge up take long enough for the Arduino to be able to measure it. I would suspect that using a long wire run would be very susceptible to noise. As such I'm going to keep the run from the circuit to the plate as short as possible (and the ground wire from the bottom probe to the circuit as short as possible as well).
On our Axis all of this is very accessible:

That is the front of the compartment where the black tank is (as you can see the probes there). I'll just be mounting the circuitry somewhere in that space.

Been experimenting with putting the ATMega to sleep. When running the circuit is consuming 25ma. Putting the ATMega to sleep reduces the current draw down to 1.4ma. I may just use a wake up circuit on the rising edge of the sense wire.
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Old 03-02-2015, 12:29 AM   #53
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I was thinking about any capacitance resulting from multiple wires within a cable. Of course, this can affect AC signals, but I am wondering how it might affect a capacitance measurement.

With todays low-capacitance cable, the capacitance would be in the pF range so it might not affect much, but if the cable got wet or influenced by moisture from being under the coach is some of my thoughts.

But I can see a very short run might be an advantage.
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Old 03-02-2015, 01:04 AM   #54
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If you wish to play, here is the circuit I'm currently using:

Attached is the Arduino code I've been running (LevelSensor.txt). Every 500ms it will send out the serial port the RC time count.

You can even use a Solo cup to test with: Wrap about 1/2 the cup with standard foil. Run a ground wire inside the cup and make sure it hits the bottom (I use a small nail to weigh down the wire) and connect the foil to the PD6/Digital pin 6 end of the 10M resistor.

When running you'll see numeric values on the terminal. As you fill the cup with water the values will increase (and if you somehow empty the cup without disturbing your test setup you'll see them fall).

The AIN1 voltage divider provides the 4.5V reference for the comparator to capture charging the RC tank cap. The ADC0 provides the 0.5V reference for the comparator to capture the discharge of the RC tank cap.
Attached Files
File Type: txt LevelSensor.txt (2.2 KB, 146 views)
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Old 03-02-2015, 12:57 PM   #55
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Thanks for the info. I might try to replicate your circuit and see if I get the same results. I'd like to compare your sensor to the commercial one.

Another issue I have with the existing monitor in my RV is the LP gauge is not very accurate. I did find that the gauge on the tank is a 0-90ohm resistive sensor. I am not sure if it is 0ohm when empty or 90ohm when full - or vice versa.

At any rate I am thinking of perhaps replacing one of the resistors on the board in the RV with a potentiometer so I can calibrate it. But my mock up board does not have a LP function, so I would have to tinker with the one on-board.

That will not happen for awhile - at least until it is warm enough outside.
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Old 03-02-2015, 01:03 PM   #56
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That is a bit harder to test: the propane gauge as its more difficult to empty and refill.
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Old 03-02-2015, 01:13 PM   #57
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That is a bit harder to test: the propane gauge as its more difficult to empty and refill.
I'll let you know in a week or two hopefully. As I previously mentioned, I'm having problems with my LP indicator so I plan to dig into it soon to see if I can figure it out. I'm not sure, but I think the transmitter on the LP tank just clips onto the mechanical gauge... a hall effect sensor

I'm a mechanical guy and not nearly as savvy with electronics as you guys so I'm not sure how far I'll get....
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Old 03-02-2015, 01:18 PM   #58
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Some of the tank monitors are hall-effect, and some are simply resistive. They are just a gauge with a sensor attached to the dial.

I am sure the resistive version is a lot cheaper, and for that reason, it's the one I'd guess most common in the RV industry.

Remember... the RV industry isn't anything if not cheap!

Similar or identical to this one:

http://www.amazon.com/dp/B003D3WPGS/...29c02f6c912d_S

The ones I found are $30~50 for a gauge, which is too expensive for testing.

I typically document my toys (RV, boat, etc) for future reference as well as each time I work on it. I found a photo of the gauge on my rig, and it looks identical to the one at Amazon. I will confirm that when I can get the rig out of the snow bank. In the mean time, I did ask the company that makes my gauge for a spec sheet. Have not yet heard back from them.
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Old 03-02-2015, 01:26 PM   #59
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Originally Posted by blw2 View Post
I'm a mechanical guy and not nearly as savvy with electronics as you guys so I'm not sure how far I'll get....
Believe, me - I am no longer the whiz I once was. But in retirement, I like to keep involved enough that I keep my mind sharp.

That is the secret to retirement - to keep your brain "excersized". The worst thing you can do in retirement is to vegetate your brain away by lack of higher thought.

Or is it; "the older you get, the younger you have to act" the secret to remaining young?

Either way works for me.
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Old 03-02-2015, 01:30 PM   #60
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The real problem with this I've just realized is that once its installed and running the wife is going to get annoyed that every time we're at a full hook-up site I'll be filling & emptying the black tank over and over again simply to admire my handiwork! LOL

(We also figure that when I do the "in situ" testing at a local campground I may gather some observers wondering what I'm doing with my black tank connected to a laptop. It may end up looking like the sewer scene in RV--although with less messy results! LOL)
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