Reply
 
Thread Tools Search this Thread Display Modes
 
Old 03-10-2010, 07:48 PM   #15
2xS
2 Rivet Member
 
2xS's Avatar
 
1971 31' Sovereign
San Diego , California
Join Date: Dec 2009
Posts: 42
Zep,

Nice post here! I was just getting started on this when looked on here to see if anyone else has tackled this project.

I noticed you used comparators and an R2R network to emulate the original Airstream design, and is that Autotrax you're using? My real question is: in your experience, did you notice the output voltages of the sensors to be more static or analog? Is it essentially just switches in the tank or is there a variable resistance to play with?


I ask because I would like to have a PIC microprocessor controlled AD/C to manipulate that data into a percent notation instead of the standard LED display. As long as there are voltage steps in between the 1/2, 3/4, full marks, it should be fairly easy. But if it doesn't work, I need to rethink my panel display.

What do you think?
__________________

__________________
Lasciate ogne speranza, voi ch'intrate
2xS is offline   Reply With Quote
Old 03-11-2010, 12:31 AM   #16
Rivet Master
 
Zeppelinium's Avatar

 
1975 31' Sovereign
1973 27' Overlander
1977 23' Safari
Palmer Lake , Colorado
Join Date: Oct 2005
Posts: 3,908
Send a message via Skype™ to Zeppelinium
What is AutoTrax? The software to generate the circuit and the PCB is free from Express PCB.

The resistance detected by the sensors as they touch the water is more digital than analog. (the slope of the solid intervals between the steps is exaggerated in the graph.) The general shape of the resistance curve has large steps as each sensor is submerged, with very small change of resistance as the tank level changes until the next sensor is submerged (or uncovered), like so:

Click image for larger version

Name:	TANK RESISTANCE.JPG
Views:	109
Size:	48.2 KB
ID:	97904

The center value of each of these steps varies, depending on the level of impurities in the water. That variability is much more significant than the total variation across one step. Ergo, the resistance ladder for the fresh tank is different than that for the gray and black (I did not test the reistance ladder for black water, just gray--that test is coming in the actual tank...).

I don't think you can devise a suitable algorithm to convert the stepwise output into a smooth slope. It would be interesting to see if you could devise a learning algorithm that could do an estimate based on the step size, but I think it would take a lot of samples.

I would have gone with a digital solution if it hadn't been for the fundamental variability in conductivity between fresh water samples.

Zep
__________________

Zeppelinium is offline   Reply With Quote
Old 03-11-2010, 12:39 AM   #17
4 Rivet Member
 
1962 28' Ambassador
1962 30' Sovereign
Currently Looking...
Webster Groves , Missouri
Join Date: Jul 2009
Posts: 309
Quote:
Originally Posted by Zeppelinium View Post
What is AutoTrax? The software to generate the circuit and the PCB is free from Express PCB.

The resistance detected by the sensors as they touch the water is more digital than analog. (the slope of the solid intervals between the steps is exaggerated in the graph.) The general shape of the resistance curve has large steps as each sensor is submerged, with very small change of resistance as the tank level changes until the next sensor is submerged (or uncovered), like so:

Attachment 97904

The center value of each of these steps varies, depending on the level of impurities in the water. That variability is much more significant than the total variation across one step. Ergo, the resistance ladder for the fresh tank is different than that for the gray and black (I did not test the reistance ladder for black water, just gray--that test is coming in the actual tank...).

I don't think you can devise a suitable algorithm to convert the stepwise output into a smooth slope. It would be interesting to see if you could devise a learning algorithm that could do an estimate based on the step size, but I think it would take a lot of samples.

I would have gone with a digital solution if it hadn't been for the fundamental variability in conductivity between fresh water samples.

Zep
Zep, What if you wanted to go the reverse? I want a "Command center" in my '62 ... how do I use modern tank sensors to feed "BIG HONKIN ROUND ANALOGUE GUAGES!"? (Kan ya' point me?)
Bob
__________________
Xbob2 is offline   Reply With Quote
Old 03-11-2010, 10:12 AM   #18
Rivet Master
 
Zeppelinium's Avatar

 
1975 31' Sovereign
1973 27' Overlander
1977 23' Safari
Palmer Lake , Colorado
Join Date: Oct 2005
Posts: 3,908
Send a message via Skype™ to Zeppelinium
Quote:
Originally Posted by Xbob2 View Post
Zep, What if you wanted to go the reverse? I want a "Command center" in my '62 ... how do I use modern tank sensors to feed "BIG HONKIN ROUND ANALOGUE GUAGES!"?
Assuming that you have the system shown in the circuit diagram in post #1, you just need to replace the original meters with the kind you like. Good luck. Have you seen the prices for analog mechanical round-faced 1 milliamp current meters lately (like the past two decades)? If you think the price-esthetics ratio is acceptable, go for it.

However, if you're talking about some other kind of "modern" sensor system, such as capacitive or pressure, I'd have to see the circuit diagram. All of these systems eventually produce a voltage that is proportional to fluid level, which can be displayed by an analog meter.

Zep
Zeppelinium is offline   Reply With Quote
Old 05-01-2010, 11:15 PM   #19
Rivet Master
 
Zeppelinium's Avatar

 
1975 31' Sovereign
1973 27' Overlander
1977 23' Safari
Palmer Lake , Colorado
Join Date: Oct 2005
Posts: 3,908
Send a message via Skype™ to Zeppelinium
Gettin' Er Done

The prototype works as intended. Yippee. Now to install and see if the water and other fluids exhibit the same impedence as the fluids I concocted (you don't want to know). A few tank fills and empties will determine the final resistor ladder values for each type of tank.

The LEDs are on one side, which still needs a bezel. There will be three switches--bright/dim, pump on, and a momentary-off-on power switch. You can see the color logic for each of the indicators. The gray and black tanks go from green at empty to red a full and the fresh water tank is just the opposite. Still need a couple of LEDs for the gray tank indicator (in the middle). The four silver standoffs in the corners will position the front panel/bezel so that there is room for the swiches--that's why the LEDs are proud of the board by about 9/16ths".

Click image for larger version

Name:	IMG_0995 board oblique-s.jpg
Views:	79
Size:	262.5 KB
ID:	101639

The components and connectors are on the other side. This side will be accessible with the bezel installed. Note that this really is a prototype. The arrows point to strip sockets that will make it easy to change the resistor ladder if adjustments are necessary. The 8-pin chip on the far side is an NE555, which can be configured as a flasher. I have it hooked up to show that the pump is on; 3 seconds off, 1/8th second on. It's a bright white flash, which ought to get one's attention even the daytime. I always seem to forget to turn the pump off when traveling. This flasher will greatly reduce the battery drain of a pump light. As it is, the LEDs only use 5ma when they're on, so that's an average current drain of about .25 ma.

Click image for larger version

Name:	IMG_0997component oblique-s.jpg
Views:	81
Size:	307.4 KB
ID:	101640


Installation may be a few days away--the snow has stopped, but it's cold and breezy.

If others are interested in this item, the PC boards can be available in three days--$55 setup and about $25 per board (the software is a free download and ordering is automatic over the Net). I'll gladly send anyone the artwork so they can order a board(s), or take orders and do a single order to save on the setup fee. I think it would take about 10 orders to make this a worthwhile effort.

If we get a minimum number of people interested, I'm going to make the layout a bit narrower in height. I found that the current board is almost the same height as the control panel opening in the early 70s trailers. Making it about 1" smaller in height will make mounting it in the existing opening/bezel easier.
Zeppelinium is offline   Reply With Quote
Old 05-02-2010, 09:07 PM   #20
Rivet Master
 
RichHog's Avatar
 
2006 25' Safari FB SE
1972 25' Tradewind
Houston , Texas
Join Date: Feb 2009
Posts: 1,142
Images: 7
Control Panel

Though I don't fully understand all the circuitry, I love seeing the process unfold. I'm probably ignorant but I haven't seen much on the forum regarding the control panel repair, replacement or troubleshooting in general. Mine (72 TW) only has the water pump switch work, which is the only critical must have component, tank levels, battery level, panel light all shot and the plastic is a little ugly. So, how do I replace the whole gizmo, not just electronics behind the face plate? Coming from the Audio/Video install arena, we often custom punch out metal plates and then engrave the faceplate. Is that the next step to make this work? Has anybody out there already done this? I for one would love to have a nice state-of the art display panel there with some sexy lights and LEDS.
__________________
RichHog is offline   Reply With Quote
Old 05-02-2010, 09:42 PM   #21
Rivet Master
 
RichHog's Avatar
 
2006 25' Safari FB SE
1972 25' Tradewind
Houston , Texas
Join Date: Feb 2009
Posts: 1,142
Images: 7
Control Panel

This is what I'm talking about. If the whole thing gets replaced then might as well put a clock in it and Battery level meter
Attached Thumbnails
Click image for larger version

Name:	DSC_0779.jpg
Views:	93
Size:	89.2 KB
ID:	101693  
__________________
RichHog is offline   Reply With Quote
Old 05-03-2010, 07:14 AM   #22
Rivet Master
 
Zeppelinium's Avatar

 
1975 31' Sovereign
1973 27' Overlander
1977 23' Safari
Palmer Lake , Colorado
Join Date: Oct 2005
Posts: 3,908
Send a message via Skype™ to Zeppelinium
Quote:
Originally Posted by RichHog View Post
...M7 72 TW only has the water pump switch work, which is the only critical must have component, tank levels, battery level, panel light all shot and the plastic is a little ugly. So, how do I replace the whole gizmo, not just electronics behind the face plate?
That's the objective--replace the whole panel with one or two panels that fit exactly in the rectangle of the bezel that you have. My 70 Caravel and 72 Overlander have exactly the problem you have and the same bezel/panel. The general scheme is loosely depicted in this drawing:

Click image for larger version

Name:	3-tank panel.jpg
Views:	70
Size:	159.1 KB
ID:	101715

But here's the rub. The early 70s tanks only have three level sensors (4 wires, one as the voltage to the tank and three return lines), while the later models, the ones with the meters, have 4 sensors. In addition, the early 70s Airstreams only have two tanks--no gray water holding tank, just black and fresh water tanks.

So there are three possible configurations of the tank level monitor:

1. Two tanks with three levels, for owners who want just a stock replacement monitor.

2. Three tanks with three levels, for owners who want to or have added a gray tank to the before-1974 Airstreams.

3. Three tanks with four levels, for owners who want to replace the bulky meter panel (which I'm going to do in my Sovereign and Safari--anyone want the old meter panel?). The meters really aren't that nifty, since they don't provide a continuous, eg, gas-gauge in your car, indication. It's more step-wise, as so (the meter indication is the reverse of this):

Click image for larger version

Name:	TANK RESISTANCE.JPG
Views:	58
Size:	48.2 KB
ID:	101717

The battery volts and amps can be provided by commerical modules for about $20 each. These can be wired to the on-off-momentary switch for the tank monitor. Temperature indicators are available for $12-ish, but might be difficult to integrate into the panel--maybe the right solution is to provide a clip to mount it proud of the panel, but so that it sorta looks like it belongs.

Anyway, the above three situations can be handled with two versions of the monitor and two front panels. Speaking of panels...


Quote:
Coming from the Audio/Video install arena, we often custom punch out metal plates and then engrave the faceplate. Is that the next step to make this work? Has anybody out there already done this? I for one would love to have a nice state-of the art display panel there with some sexy lights and LEDS.
What does a panel cost if they are done in onesey-twosey kinds of numbers? Can these be done in 0.060 or 0.125 aluminum or is there a plastic that would be suitable? We can take a detailed discussion off line, but I'm interested in whether the labels for the tanks, eg, BLACK GRAY WATER, would be engraved in the panel or would be a backlighted open window, etc. Right now my biggest issue with the panel is the spacing of the LEDs. They are 5mm diameter and I wouldn't want them to have more than about 2mm of space between them in a finished product.

I'm open to bartering a monitor ...

Zep
Zeppelinium is offline   Reply With Quote
Old 05-03-2010, 08:09 AM   #23
Rivet Master
 
Zeppelinium's Avatar

 
1975 31' Sovereign
1973 27' Overlander
1977 23' Safari
Palmer Lake , Colorado
Join Date: Oct 2005
Posts: 3,908
Send a message via Skype™ to Zeppelinium
Quote:
Originally Posted by 2xS View Post
... My real question is: in your experience, did you notice the output voltages of the sensors to be more static or analog? Is it essentially just switches in the tank or is there a variable resistance to play with?
...

Here's data using the same resistor ladder and the same faux sensor board in three different glasses of fluids. It is interesting to see that there was almost no voltage variation in the black water as the sensor board was slipped up and down, compared to the other liquids. I was also somewhat perplexed that the voltage jumped when just the driven sensor hit the fluid. I wouldn't have expected any change until two sensors were in the fluid, since the circuit isn't complete until then. What have we here, a battery?

Click image for larger version

Name:	monitor volts.jpg
Views:	69
Size:	82.5 KB
ID:	101718

Even with the variability, the voltages are monotonic. As soon as the weather improves, I'm going to get real data from the tanks in the Overlander (water and black, no gray). I expect some difference will show up due to the tank size and sensor spacing.

I calculated, based on the data from the glass of fluid, that the equivalent impedence of the fluids are:

Water - 8.2K
Gray - 5.1K
Black - 3.3K

Zep
Zeppelinium is offline   Reply With Quote
Old 05-09-2010, 04:22 PM   #24
Rivet Master
 
Zeppelinium's Avatar

 
1975 31' Sovereign
1973 27' Overlander
1977 23' Safari
Palmer Lake , Colorado
Join Date: Oct 2005
Posts: 3,908
Send a message via Skype™ to Zeppelinium
Yippee, finished! And much simpler, don't you think?

Click image for larger version

Name:	circuit.jpg
Views:	113
Size:	222.0 KB
ID:	102176

Zep

(apologies and thanks to XKCD)
Zeppelinium is offline   Reply With Quote
Old 05-10-2010, 12:14 AM   #25
Rivet Master
 
RichHog's Avatar
 
2006 25' Safari FB SE
1972 25' Tradewind
Houston , Texas
Join Date: Feb 2009
Posts: 1,142
Images: 7
Control panel

I would add a decent sized LED clock to the panel as well. The av ones are black metal with silver etched lettering usually 19" long to fit standard cases and equipment racks, also 1-6" high
__________________
RichHog is offline   Reply With Quote
Old 05-10-2010, 02:05 AM   #26
Maniacal Engineer
 
barts's Avatar
 
1971 25' Tradewind
Menlo Park , California
Join Date: Jan 2010
Posts: 1,223
Images: 1
Blog Entries: 4
Cool - I've not yet dug into why our '71 Tradewind's sensors/indicator doesn't work; this has started me thinking... thanks for the info on how these sensors work.

One could also use a PIC microprocessor to convert the analog readings into digital values, and then control the output LEDs directly; this would let one tweak the settings via a PC. http://sparkfun.com is a fascinating supplier of interesting semiconductor stuff for hobbyists; the sensor devices are particularly sophisticated (GPS, carbon monoxide, accelerometers, ...) . The magnetic level sensor seems particularly useful....

One can imagine a small display cycling through the available data (voltage, battery current, tank levels, etc).

As far as making panels goes, 1/8" 6061 T6 is really easy to work in the home shop. Cut shy of the line, and file to final size; it's easy to hold a few thou w/ a fine file. Get a hold of some layout dye and layout the holes, etc, on the back side of the panel. Center punch the holes, and drill on a drill press. Square/rectangular holes are easily filed from round, too.

- Bart
__________________
Bart Smaalders
Menlo Park, CA
http://tinpickle.blogspot.com
http://smaalders.net/barts
barts is offline   Reply With Quote
Old 05-10-2010, 01:28 PM   #27
Rivet Master
 
Zeppelinium's Avatar

 
1975 31' Sovereign
1973 27' Overlander
1977 23' Safari
Palmer Lake , Colorado
Join Date: Oct 2005
Posts: 3,908
Send a message via Skype™ to Zeppelinium
Quote:
Originally Posted by barts View Post
... The magnetic level sensor seems particularly useful....
Do you have one? I can't tell anything about how it works, how to install, how to adjust for various depth of tank, etc. It would be great to have a continuous analog level reading!

Zep
Zeppelinium is offline   Reply With Quote
Old 05-11-2010, 12:26 AM   #28
Maniacal Engineer
 
barts's Avatar
 
1971 25' Tradewind
Menlo Park , California
Join Date: Jan 2010
Posts: 1,223
Images: 1
Blog Entries: 4
Quote:
Originally Posted by Zeppelinium View Post
Do you have one? I can't tell anything about how it works, how to install, how to adjust for various depth of tank, etc. It would be great to have a continuous analog level reading!

Zep
I don't have one, but from the description it's an self-adhesive potentiometer, with the wiper in the form of a magnet. You stick it to a tube that contains a float w/ a magnet inside of it, and the small magnet inside the pot. tracks the one inside the float that's inside the tube. Plumb the tube top and bottom to track the level inside the tank and you're set.

- Bart
__________________

__________________
Bart Smaalders
Menlo Park, CA
http://tinpickle.blogspot.com
http://smaalders.net/barts
barts is offline   Reply With Quote
Reply


Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 
Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Micro Pulse Tank monitor calibration Silvertwinkie Plumbing - Systems & Fixtures 98 11-03-2014 02:09 PM
Micro-Pulse tank monitor blues dlb435 Waste Systems, Tanks & Totes 11 07-14-2009 02:53 PM
looking for tank monitor replacement parts rec Plumbing - Systems & Fixtures 3 08-04-2008 09:18 AM
Digital TV jcanavera Audio, Video & TV 3 02-02-2007 11:51 AM
Tank Monitor Help pmclemore Electrical - Systems, Generators, Batteries & Solar 4 01-31-2006 01:41 PM


Virginia Campgrounds

Reviews provided by




Copyright 2002- Social Knowledge, LLC All Rights Reserved.

All times are GMT -6. The time now is 07:28 PM.


Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2017, Jelsoft Enterprises Ltd.

Airstream is a registered trademark of Airstream Inc. All rights reserved. Airstream trademark used under license to Social Knowledge LLC.