I've lost my URL for an expanded scale voltmeter. The only parts used in the circuit were two LM78LXX regulator ICs. The sum of the regulator voltages is picked to equal the minimum scale reading. Then, the minimum plus the voltmeter were the maximum scale reading. Example: An LM78L05 and a LM78L08 with a 6 volt meter would have 0 = 13V and FS = 19V. I thought it was EDN but searched the site and didn't find it. Anybody have it? Thanks, Mike
Sounds way too complicated for an expanded scale meter.. add a zener in series with the meter. The zener provides the low (zero) reading, and the meter is scaled with a resistor for the max. Example: A 12V zener in series with a 6 volt meter makes the scale read 12-18 volts. Choose meter sensitivity and zener power to handle available current.
-- Dave M MasonDG44 at comcast dot net (Just substitute the appropriate characters in the address) Life is like a roll of toilet paper; the closer it gets to the end, the faster it goes.
Use something like a TL431 or its CMOS equivalent, and get it dead-nuts-on.
...Jim Thompson
--
| James E.Thompson, P.E. | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC\'s and Discrete Systems | manus |
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"DaveM" wrote in news:i9OdnaqDJfq3N6TUnZ2dnUVZ snipped-for-privacy@giganews.com:
most zeners aren't going to work at the low current burden most voltmeters have. Plus they aren't that accurate in voltage rating,and have lousy "knees".
-- Jim Yanik jyanik at kua.net
This might be what you have in mind:
Ed
and
series
What good are dead nuts?
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Thank you Ed, that's the one I was looking for. Upon further review I notice that one of the regulators is a negative regulator (79Lxx). Anyone have any comments about the operation of the circuit? I'm about to build a 40v to 60v metering circuit for my 48v deep cycle battery powered gokart. Thanks, Mike
As she once said "it's always something" I'm not locating a combination of regulators that sums to 40v and the regulators have max spec of 35v. Maybe a voltage divider on the battery, so I'm measuring 20v to 30v or better 10v to 15v. Mike
On a sunny day (Sat, 6 Dec 2008 05:48:45 -0600) it happened "amdx" wrote in :
Thanks, Mike
Have you considered using a PIC with build in ADC, connected to 2 seven segment LED displays, to get a nice 0-99 digital display?
This guy's got an intresting Hack for converting a cheap DVM into a panel meter.
Scroll down to Digital Ammeter modules
Well, no not that route, but if I was going make a new dashboard I would probably go with digital displays instead of analog panel meters. Mike PS. Might do that after I get the new batteries installed and wired, then wire it for the new battery charger. Oh, and the other projects,1 wire temperature monitoring system with about
20 temp sensors, and then building the solar collectors for hot water. and then there are the honey do's. :-)
Hans does some neat stuff. I remember years ago I saw those meters at the Orlando hamfest for $9.99 and thought that was amazing, now I've seen them for $2.99. That's amazinger. How long before amazingest.
way to draw an obfuscated diagram!
this is what it is (with the devices oriented more conventionally)
AFAICT the 79L05 is not well suited to sourcing current neither is the 78L05 a good sink.
I have not found a datasheet that specifies a reverse current.
Also when the voltage drops below 10 the voltmeter will be reverse-biased
It looks to me to be another of the junk circuits that EDN publishes occasionally.
it's using the devices outside of their published operating parameters (negative output current)
use TL431 instead like jim suggests actually, use 2 as you can only get 36v drop from each also using 2 makes makes biasing easier,
this is basically what the EDN circuit was trying to be:
Ra and Rb are chosen to set the voltage at 20V (per part) Rc is chosen to pass the 1ma needed by the TL431 for regulation and the current that Ra+Rb take with 20V across them. 2.5v on the reference pin 20V on the cathode so Ra:Rb 17.5:2.5 = 8:1 maybe Ra=16K Rb=2K Rc=8.1K possibly one of the Ra should be replaced with 15K in series with a 2K trimmer. Otoh, the meter may have enough adjustemnt to be mechanically zeroed. with undervoltage the maximum reverse bias will be smaller than 20V and so probably not enough to damage the meter.
I have to question why an old guy would use the phrase "dead-nuts"?
I ain't old, I'm well-aged ;-)
...Jim Thompson
-- | James E.Thompson, P.E. | mens | | Analog Innovations, Inc. | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | Phoenix, Arizona 85048 Skype: Contacts Only | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at
-- It\'s an old phrase that came about when one nut was turned, against a threaded shaft, to make an adjustment and another nut was tightened against the first one to lock it in place. JF
I've heard various suggested etymologies, but none that captured the actual meaning of the phrase. To me, "dead nuts" is a slightly more serious sounding version of "right on the nose".
The most plausible one I've heard is that it originally described a particularly well-aimed blow below the belt--i.e. "dead on, in the nuts". (After all, that's pretty similar to the etymology of "right on the nose".)
Cheers,
Phil Hobbs
It's a very common expression in industry, especially in machining and stuff. It simply means "within a neglible tolerance".
Hope This Helps! Rich
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