Reply
 
Thread Tools Search this Thread Display Modes
 
Old 11-15-2009, 03:35 PM   #1
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
Tank Monitor replacement - digital

OK, I admit I mentioned doing this a couple years ago. One good thing about snow and cold--it encourages/allows you to get back in the lab.

Very short tutorial: the older 70s, and earlier, tank monitors use four wires to report the water level to a circuit card with small light bulbs that illuminate to crudely indicate fluid level. The newer 70s (I don't know when it changed, but some time between 72 and 75) use two wires to send a varying voltage (5 steps, which is a bit more resolution than the 4-wire system) which drives small analog meters. Although these methods are very different from an electrical standpoint, a very similar circuit can be built to detect the two different kinds of inputs and turn on LEDs in the same way the old system turned on the light bulbs.

Note: the following description is preliminary and will most likely be modified once I can make the first prototype. This information is posted so that others can make inputs, both improvements and corrections. I'd rather have a correction than a smoke test.

Two-wire system: this system has four sensor probes and one driver probe. Using resistors in series with the probes, the four sensor probes can provide 5 output levels (the fifth level is zero--no contact with water). Here's where I might need a little help--it's too cold here to experimentally fill and empty my tanks, so had to improvise in the lab. When I used 9 volts to drive the probes, I got the following outputs. If you measure and existing set of probes that are connected to 12 volts, you should get something like the numbers in the right column.

Name:   voltage table.jpg
Views: 3484
Size:  30.5 KB
For reference, this is the schematic of the original meter circuit:

Click image for larger version

Name:	meter circuit-s.jpg
Views:	1477
Size:	151.9 KB
ID:	91061

A quad voltage comparator can be used to detect the voltage input level and turn on an LED ladder. It's a very inexpensive circuit, around $6 per tank, plus the experimenters punch board from some place like Radio Shack. Laying out a printed circuit board is helpful in seeing how it might look, even if it's made by hand. It looks like the total board area is 3"x3". The LED columns are 1" appart and are 0.9" long.

Click image for larger version

Name:	2-wire sch.jpg
Views:	362
Size:	187.4 KB
ID:	91058 Click image for larger version

Name:	2-wire pcb.jpg
Views:	233
Size:	440.6 KB
ID:	91057

The four-wire (older) version is very similar, but a bit simpler. As each sensor contacts water, its LED illuminates.

Click image for larger version

Name:	4-wire sch.jpg
Views:	396
Size:	163.4 KB
ID:	91060 Click image for larger version

Name:	4-wire pcb.jpg
Views:	222
Size:	421.0 KB
ID:	91059

The board would function only when a "press to test" switch is pushed. I've considerd putting in a switch with a momentary function and an "on" function. All the LEDs would illuminate at the water level and below (eg, all the LEDs below the current level would also illuminate). Any input on alternate functionality will be considered. BTW, there is a reason for using 9V as the (+) power--the HF meters work off of 9V and I intend to rip a couple of those suckers apart to provide an indication of battery voltage and current. More on that mod later.

Zep
__________________

Zeppelinium is offline   Reply With Quote
Old 11-15-2009, 06:54 PM   #2
Rivet Master
 
RichHog's Avatar
 
2006 25' Safari FB SE
1972 25' Tradewind
Houston , Texas
Join Date: Feb 2009
Posts: 1,142
Images: 7
Sensor for water tank

Is this something you would manufacture and sell? If so I'm in as my 72 TW doesn't have much functionality on the control panel and it seems that info on it's components is missing on the forums.

Thanks for your efforts, could you use different colored LEDs, say like green for full, yellow for low and red for empty?

Richard
__________________

__________________
RichHog is offline   Reply With Quote
Old 11-15-2009, 07:19 PM   #3
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
Yes, different LEDs - green, yellow, orange, red.

No, not sell. Once I check it out completely, I'll put the plans here. If you haven't soldered DIP-type integrated circuits, I'm sure you can find a ham or a computer kid in your area that can do it. It will be simple.

Zep
Zeppelinium is offline   Reply With Quote
Old 11-16-2009, 10:26 PM   #4
Rivet Master
 
RichHog's Avatar
 
2006 25' Safari FB SE
1972 25' Tradewind
Houston , Texas
Join Date: Feb 2009
Posts: 1,142
Images: 7
LEDs

Hey I built a Heathkit Color TV back when you had to solder ALL the components on the boards. Will give it a try.
__________________
RichHog is offline   Reply With Quote
Old 11-17-2009, 11:43 AM   #5
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
2-wire tank monitor circuit

The circuit is changed so the LEDs come on rather than go off as the water level rises. Also a bit of simplification to the input resistors. The breadboard works per expectations. No other guarantees, express or implied! It appears that this could be built on a single layer PC board, so there should be a minimum of jumper wires when it's built on an punch board.

Click image for larger version

Name:	2-wire_c_sch.jpg
Views:	246
Size:	233.1 KB
ID:	91205 Click image for larger version

Name:	2-wire_d_pcb.jpg
Views:	169
Size:	285.1 KB
ID:	91206

The bread board tested 4-wire circuit will be along shortly.

Zep
Zeppelinium is offline   Reply With Quote
Old 11-17-2009, 03:38 PM   #6
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
4-wire tank monitoring circuit

Here's the 4-wire circuit and layout. The electronics are somewhat simpler and there is a spare comparator, in case you have an application where one more wire/indicator is needed.

Click image for larger version

Name:	4-wire_sch_b.jpg
Views:	419
Size:	190.1 KB
ID:	91211 Click image for larger version

Name:	4-wire_pcb_e.jpg
Views:	170
Size:	351.3 KB
ID:	91212

I'm guessing that this system was used before 1975 and the addition of the gray holding tank. So you ony need two of the modules, not three. But just in case, the layout provides for three.

Zep
Zeppelinium is offline   Reply With Quote
Old 11-17-2009, 03:54 PM   #7
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
Broken wire?

If you've got a 4-wire system and you have a broken wire, or if you want to add a sensor (stainless steel screw-in post, really) to provide an additional water level reading, you can easily convert your 4-wire system to two wires. Just use a small piece of insulated board to mount the resistors and some kind of connector for the external wires and mount it near the tank. You can now use the 2-wire monitor module for each converted tank.

Click image for larger version

Name:	wire conversion.jpg
Views:	357
Size:	78.1 KB
ID:	91214

I'm going to convert my Caravel and Overlander to the 2-wire system. I doubt I'll add another sensor, however, just keep a 3-level indication capability.

Zep
Zeppelinium is offline   Reply With Quote
Old 11-18-2009, 02:02 PM   #8
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
building a prototype

I've been assuming that anyone who would try this is familiar with DIP prototyping tools. If not, here's what it takes to get started. Radio Shack has the layout board for about $20. You'll also need a small 12V power supply, like one of the types where the whole unit hangs on the 110V plug. It's also good to know which end of the LM339 has pin #1.

Click image for larger version

Name:	IMG_0363 bread board-s.jpg
Views:	180
Size:	169.5 KB
ID:	91248 Click image for larger version

Name:	IMG_0365 ic INDENT-S.jpg
Views:	142
Size:	125.2 KB
ID:	91249

When you've got the bread board model figured out, you'll want to make something a little more portable, something that might actually be useful (temporarily) in the Airstream. That requires soldering the components onto a prototyping board. There are three kinds--bare, isolated-dots, and bussed. The bussed boards are easiest to work with, but the finished prototype will be a little larger, due to the component placement restrictions of the busses, than the isolated-dot type board.

Click image for larger version

Name:	IMG_0361 boards front-s.jpg
Views:	141
Size:	161.5 KB
ID:	91250 Click image for larger version

Name:	IMG_0362 boards back-s.jpg
Views:	151
Size:	206.1 KB
ID:	91251

The odd shapes are the result other projects the nibbled away at the orginal board(s).
Zeppelinium is offline   Reply With Quote
Old 11-18-2009, 02:10 PM   #9
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
building a prototype - II

This prototype did not follow that PCB layout pictured earlier. In addition, during the prototype testing there were some changes made to the schematic, so use the one in this post, not any of the earlier ones. The series resistors for the LEDs were adjusted to get the apparent brightness of the colors to match. The red LEDs are more efficient than the green and yellow, so they require a bit higher resistance in order to dim them down a little.

One of the major differences in this prototype is the use of a 10-pin socket for the voltage divider resistors. This will allow changes for the higher conductivity of the black and gray water (see tables in the next post).

Click image for larger version

Name:	IMG_0367 front view-s.jpg
Views:	151
Size:	145.5 KB
ID:	91252 Click image for larger version

Name:	IMG_0372 back view-s.jpg
Views:	141
Size:	296.8 KB
ID:	91253

Click image for larger version

Name:	IMG_0371 side view-s.jpg
Views:	152
Size:	155.9 KB
ID:	91254 Click image for larger version

Name:	IMG_0366 sensor strip-s.jpg
Views:	170
Size:	141.0 KB
ID:	91255

You can see that the test sensor strip is pretty simple.

Here's the correct schematic. The schematic is the same for all type tanks--fresh, gray, and black. But the input voltages are different due to the differing conductivities, so the resistor values for R1-R5 are different (see next post). The values here were nominal for fresh water in the lab and will most likely change for the tank(s).

Click image for larger version

Name:	2-wire_sch_e.jpg
Views:	197
Size:	337.6 KB
ID:	91256
Zeppelinium is offline   Reply With Quote
Old 11-18-2009, 03:00 PM   #10
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
The input voltage from the tank(s) is influenced by the conductivity of the water in the tank. Clean water is not very conductive. Impurities, especially salt, increase its conductivity dramatically. The following tables show the differing inputs that can be expected from the three types of tanks (don't ask how). Only actual road test will confirm these values. In addition, the type of tank may have some unexpected influence, eg, tall versus flat tanks.

Click image for larger version

Name:	resistor ladders.jpg
Views:	153
Size:	137.5 KB
ID:	91257

The values aren't grossly different, but the different conductivity does move the switching voltage enough that the fresh tank resistors definitely wouldn't work for the black tank. I suppose this is why the meters in the original monitor had an adjustable resistor in the circuit. I'm going to think about whether a variable resistor (one for each monitor) would be a more general solution for this design, too.

One interesting phenominom is that the black tank voltage decays very much more slowly when the sensors are taken out of the water than for the other two samples (ugh). The empty voltage before the sensors are wet is around 2.4 volts, but when they are removed after being wet, the voltage slowly decays down to about 2.8 volts and then very slowly to lower values. This is probably not a problem, unless you're filling and emptying your black tank really quickly...

happy soldering, Zep
Zeppelinium is offline   Reply With Quote
Old 11-18-2009, 06:39 PM   #11
Rivet Master
 
goransons's Avatar

 
1963 22' Safari
1955 26' Cruiser Overlander
Yakima Valley , Washington
Join Date: Jul 2007
Posts: 2,168
Images: 10
Blog Entries: 1
Send a message via MSN to goransons
its just crazy.. I mean, is there anything you don't do?
__________________
Scott & Megan
VAC LIBRARIAN
Restoring Wally Byam's 1955 26' European Caravan Trailer!
LOOKING FOR A COUNTER HEIGHT KREFFT REFRIGERATOR!!
goransons is online now   Reply With Quote
Old 11-18-2009, 06:47 PM   #12
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
Thanks, Scott. I will admit I'm not a very good ballerina and I don't call my mom often enough. The truth is, I do a lot of stuff, but none of them as a true expert. So beware.

Zep
Zeppelinium is offline   Reply With Quote
Old 11-18-2009, 06:53 PM   #13
Rivet Master
 
silverleeper's Avatar
 
1967 22' Safari
1960 Caravel
Edmonds , Washington
Join Date: Aug 2004
Posts: 2,499
Images: 8
Quote:
Originally Posted by Zeppelinium View Post
Thanks, Scott. I will admit I'm not a very good ballerina Zep

Some say you have the legs of a ballerina.
__________________
Lee

1973 F-250 4X4 390
1965 Chevy Suburban 454
AIR 6030
WBCCI 4258
TCT

silverleeper is offline   Reply With Quote
Old 11-21-2009, 11:45 AM   #14
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
Final Monitor - maybe

Here's the final monitor design. It's for the 2-wire system. When you look at the printed circuit you can see 3 modules on the right side that are intended to be cut off and installed at the tank to convert a 4-wire system to 2 wires.

The only change contemplated at this time is to spread out the LEDs by an additional 0.1". This design accomodates 6.5x3.5 millimeter rectangular LEDs, which are hard to find. The alternative is smaller rectangular LEDs or slightly larger round LEDs.

The cost of a single board with three monitors is $32 in small quantities. If more than 10 members are intersted, it would lower the cost to about $22. The order could be soon, but definitely before the end of December. PM me if you are interested.

Click image for larger version

Name:	rev-K_sch.jpg
Views:	181
Size:	380.4 KB
ID:	91349

Click image for larger version

Name:	rev-K_full.jpg
Views:	146
Size:	1.13 MB
ID:	91350

Click image for larger version

Name:	rev-K_top.jpg
Views:	147
Size:	762.3 KB
ID:	91351

Click image for larger version

Name:	rev-K_bottom.jpg
Views:	149
Size:	770.9 KB
ID:	91352

Click image for larger version

Name:	rev-K_silk.jpg
Views:	150
Size:	452.0 KB
ID:	91353

Enjoy, Zep
__________________

Zeppelinium 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 07:51 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.