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Old 05-16-2010, 03:19 PM   #29
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the home stretch

Ugly monitor panel out...(avoiding any discussion of the "electronics")

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New monitor panel in...

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You can see the prototype is fairly far along. It copies the original angle and will do fine, but the face seems a bit too recessed and the angle could be somewhat less, say 12-15 degrees. For my standing height (the exact average man, circa 1975), the panel is looking over my head.

The volt and current meters are $7 units that require an isolated 9V battery for power. I was hoping to use power off the monitor board, but that got too complicated. The saving grace here is that it only takes two screws to remove the unit from the dome, so getting at the battery won't be too big a problem. Besides, the thermometer will also need a battery change.

Speaking of the thermometer (and always looking for the cheap solution) I modified this popular unit to get a flat face on it so it could be pressed up against the back of the panel. You have to sand off the built-in light lens and remove the button switches (these can easily be remoted outside the unit).

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You can see where the thermometer (about $11) fits into the panel. It turns out the thermometer LCD display is the same height as the volt and ammeter displays. Lucky day. The final panel should look something like this (laser cut from 3.32 plastic (blue on surface and white inside, making white lettering). I've been told it will cost about $25, which is too low to believe.

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Zep
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Old 05-17-2010, 10:01 AM   #30
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Looking Good!
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Old 05-17-2010, 10:36 PM   #31
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Not for everyone

The weather has actually acted like spring yesterday and today--motivation to get out of the lab and take some real data. Here's what the fresh water tank looks like. Note the visual estimate of where the sensors are versus the tank draining time (yes, I did sit there for 76 minutes, twice, to get the data). Ack. The good news is that the sensor performance and measured voltages were very well behaved. I may need adjust the resistor ladder a bit to get the voltages right smack dad in the middle of the detection ranges, but I'm pretty happy with the results.

I whipped up the test circuit so I could get the data without having to install the whole monitor panel. The test circuit exactly duplicates the input side of the tank monitor, except that the excitation voltage from the battery is 9.6V versus the nominal 9V from the monitor circuit. I normalized that difference out in the chart.

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Note the odd spacing of the sensors (estimated positions are described in the boxes in the chart). It's difficult to get an eyeball in position to even see the suckers, much less measure them (probably could have thought more about this when I built the cabinets), so the positions are just eyeball estimates. The drain time may be a better indication of what level the sensors are really reporting. Need I repeat that I really think the drain diameter could have been better thought out when the tank was installed...

Black tank data tomorrow. It will only be two points, since the original early 70s black tanks only report two levels and I don't want to contemplate slowly filling the black tank...

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Old 05-20-2010, 09:52 PM   #32
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Ready for Albuquerque, finally. The last big discovery today was that the water pump puts alot of trash on the 12V line and will fry unprotected ICs. So another day goes by not doing woodwork, but now the monitor has a fairly robust filtered power supply.

I'm going to try out some night lighting. The red is a little too "submarine" but it's fine for the prototype. The "production" model may have soft white or amber. These lights are any time the monitor is on, although it would be easy to put in a push button for on demand illumination.

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The LEDs a in the 1/2" maple frame, aimed back at approximately a 60 degree angle.

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Onward and upward...

Oops, one more thing. Gotta make a shunt for the ammeter for battery current. One foot of #10 copper and a couple of heavy duty wire cleats should do it. We'll see. What you want is a very high current resistor that provides one millivolt per amp.

Zep
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Old 05-21-2010, 08:50 AM   #33
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how many 6 packs of beer have gone into the R & D on this thing? Maple wood framing? Very cool!
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Old 05-21-2010, 10:09 AM   #34
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Shunt

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how many 6 packs of beer have gone into the R & D on this thing? Maple wood framing? Very cool!
two-buck Chuck, my brother. I drank all the beer I ever needed back in SEA. Not to mention losing money playing poker.

The good (or should I say great) news this morning is the shunt works waay better than expected. Calibration is a bit of a challenge, since it's hard to find 1% precision power resistors in the 1-4 ohm range. Never-the-less, I think it's close, within about 5%. I used a 6 amp/12V power supply and two 4 ohm/50W resistors and two meters to get the best readings I could.

The shunt is pretty basic. If you failed to retain the fuse block from your old Univolt, which had a nice copper plate shunt on it, you can make one for $2.08. If you use #10 wire, the wire tables say you need 12.01 inches of wire for 0.001 ohm (roughly speaking). I wound up using 10.25 inches. If my calibration is off, the shorter wire means the meter will be showing less current than is actually flowing.

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Used an scrap piece of plastic from my Sovereign tank welding experiment as the backing piece. A dry piece of wood would work fine, since the voltage across the terminals/lugs will always be less than 100 millivolts.

The electrical installation is a bit counter-intuitive for me--I'd have thought these things go in the positive lead of the battery. However, putting it in the negative (common) lead ensures that the wires from the voltmeter are essentially at ground potential. This floats the battery above ground just slightly.

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The fuses in the voltmeter wires are problematic for me. It's ultra-safe, but it would take a short to ground in the wire on the high side of the shunt, close to the shunt, like 12" or less, in order to drive enough current through the small wire to be dangerous. The voltmeter wires have approximately 8 times the resistance of the #10 wire in the shunt, so the preponderance of battery current would contiue through the large wires (unless the battery common becomes open below the shunt). The original fuses are 8" down the wire. This 8" is the most "dangerous" part of the length, so the fuse on the other wire protects this short length. So, there are scenarios where the fuses could be helpful. Vanishingly small scenarios. But I left them in the circuit. You could be just as safe with one fuse in the low side wire (any other insight would be appreciated).

How well does the "amp meter" (the combination of the 200 mv voltmeter and shunt) work? Great! I was concerned that the long wires from the back of the Overlander to the front dome would be noisy. The meter is 3-1/2 digits, so it measures down to 0.1 mv, or 100 milliamps of current. With just a few minutes of observation, the meter jumps around a bit in the tenths digit (1 count only). It shows the water pump pulling 6.5 amps in open flow, ramping up to 7.4 amps as the pressure builds up to shutoff. It also shows turning the porch light on and off (less than 100 ma), and the radio (400 ma). When I get a long enough arm, I'll check what it shows for the hitch jack.

I just can't believe it's this stable and precise. The old analog meters were essentially useless.

Zep
(playing Meatloaf and Joe Cocker--happy happy)
saving the folk music for another day!

PS--I forgot to mention up in post #23 that the temperature gauge looks good--it's right up flat against the panel, looks like it was designed just for this.
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Old 05-22-2010, 12:46 AM   #35
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How well does the "amp meter" (the combination of the 200 mv voltmeter and shunt) work? Great! I was concerned that the long wires from the back of the Overlander to the front dome would be noisy. The meter is 3-1/2 digits, so it measures down to 0.1 mv, or 100 milliamps of current. With just a few minutes of observation, the meter jumps around a bit in the tenths digit (1 count only). It shows the water pump pulling 6.5 amps in open flow, ramping up to 7.4 amps as the pressure builds up to shutoff. It also shows turning the porch light on and off (less than 100 ma), and the radio (400 ma). When I get a long enough arm, I'll check what it shows for the hitch jack.

I just can't believe it's this stable and precise.
Nice work!

The panel in our '71 Tradewind is mostly non-functional; I look forward to getting the basics on the trailer working so I can try my hand at this sort of thing.... I'm torn between something completely digital based on a Mimo touch screen and a steam-punk sort of polished brass panel w/ black Bakelite knobs & switches .

Oblig. geekishness:

The reason the digital meters are stable is that they use integrating A/D converters - they essentially average the voltage over each time interval. This is very handy, since no input filtering is required to prevent aliasing due to noise....
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Old 05-22-2010, 06:05 AM   #36
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Quote:
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...The reason the digital meters are stable is that they use integrating A/D converters - they essentially average the voltage over each time interval. This is very handy, since no input filtering is required to prevent aliasing due to noise....
I should have thought of that. These things are slow, like 2-3 conversions a second. That's one heck of a low pass filter. I'm used to 12-bit A/Ds that do conversions in the low kHz range. Now all I need for the "production" version is an isolated DC-DC converter so I can get rid of the battery.

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Old 05-23-2010, 10:34 AM   #37
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Now all I need for the "production" version is an isolated DC-DC converter so I can get rid of the battery.

Zep
You need a meter w/ a common ground like this one for voltage; this will work w/ your shunt.

Here's a larger one that has a back-light....

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Old 05-23-2010, 12:12 PM   #38
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BARTS, I appreciate your inputs. I'm refining the design before I modify my other trailers, so keep them coming.

I like these panel meters a little better (second one down). They have a smaller bezel, match the temperature unit in appearance and window size, are a bit cheaper (and use the same basic electronics) and draw only 1 ma.

The mechanical installation is the big issue for me at this point. I'm looking at ways to eliminate as many wires as possible and make sure the panel is easy to install and easily removable for maintenance, should that be necessary.

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Old 06-08-2010, 07:44 PM   #39
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Finished

The cosmetically correct version is finally together.

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As you can see from the back, the panel consists of several different modules, which means it can be configured as a full 5"x22" replacement for the orginal early 70s monitors, or can be physically rearranged into other shapes, even as small as just the monitor itself (in about 4"x4").

One-off panels are about $30, so making a different arrangement is not a big deal. The panel is 1/8" plastic that is laser-cut. I've added an 0.032 aluminum back, but it's still very flexible. It needs to be in a frame (see post #32 above) to provide stiffness and some protection.

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Old 06-09-2010, 02:54 AM   #40
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Nice work! very clean, professional and appropriate for a 'stream.

- Bart
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Old 06-10-2010, 09:58 AM   #41
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Very nice work. sign me up!
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Old 06-15-2010, 12:12 PM   #42
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Per the briefing at the Restoration Rally last weekend, the monitor and the rest of the panel are modular, so it can take any shape (within limits) that fit your location and design objective.

Here's four examples of just the monitor and the pump switch.

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The items in BLUE (the LEDs) and the four small mounting screw circles are established by the PC Board and cannot be moved in relation to each other. However, you can have some or all of the LEDs, per the number of sensors you have (or will have), and two or three tanks. The other option that is shown is you can eliminate the bottom row of LEDs (they are on all the time the monitor is on--I hated the old system where if the tank was empty, no lights came on at all). You can move the BLACK text and the RED switches and text around where ever you want them. You can add other text, and even a label like "My Special Cool Ambassador Monitor." You can eliminate the pump indicator (or make it constant, eg, non-flashing) and/or the pump switch. You can also eliminate the bright/dim option. I've found that I generally like the LEDs on dim and the pump flasher on bright. If you set up your panel that way, you can save some parts and a $5 switch.

You can put the volt and amp meters above, below, or to the side, if you want them.

You can add a clock or a temperature device of your own choosing, but you have to figure out the window dimensions and placement, totally. And how you're going to mount them/it mechanically.

The plastic front plate can be used (carefully) as a drilling and filing template--the laser cuts out the holes, but only removes the top color layer for the text.

It appears that we have 4-5 interested parties from the Rally. However, all interested parties must PM me an state their intentions and the options they want in their panel. I'll cooperate with each person to get the panel design right. The PC Board is the same for all, you just don't put in all the parts.

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