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Expanded Voltmeter circuit

A

amdx

Jan 1, 1970
0
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
 
J

Jim Yanik

Jan 1, 1970
0
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.

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".
 
E

ehsjr

Jan 1, 1970
0
amdx said:
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
This might be what you have in mind:
http://www.edn.com/archives/1994/012094/02di2.htm

Ed
 
A

amdx

Jan 1, 1970
0
ehsjr said:

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
 
A

amdx

Jan 1, 1970
0
amdx said:
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
 
H

Hammy

Jan 1, 1970
0
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

This guy's got an intresting Hack for converting a cheap DVM into a
panel meter.

Scroll down to Digital Ammeter modules

http://www.hanssummers.com/radio/psu/index.htm
 
A

amdx

Jan 1, 1970
0
Jan Panteltje said:
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?

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. :)
 
A

amdx

Jan 1, 1970
0
Hammy said:
This guy's got an intresting Hack for converting a cheap DVM into a
panel meter.

Scroll down to Digital Ammeter modules

http://www.hanssummers.com/radio/psu/index.htm
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. <:-\
 
J

Jasen Betts

Jan 1, 1970
0

way to draw an obfuscated diagram!

this is what it is

(with the devices oriented more conventionally)

+ --+--------.
| |adj
| in | out
| .--[79L05]-----.
| | |
| | (V)
| | |
`--|--[78L05]-----'
|in | out
| |adj
- -----+-----'

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.
 
J

Jasen Betts

Jan 1, 1970
0
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?

it's using the devices outside of their published operating parameters
(negative output current)
I'm about to build a 40v to 60v metering circuit for my 48v
deep cycle battery powered gokart.
Thanks, Mike

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] : | :
| | : ,---' :
[Rc] +---:--/ \ :
| | : --+-- :
| [Rb] :...|...:
| | |
| .---+-------+
| | |
| | METER
| | |
`-|---+-------+
| | |
| | ....|....
| [Ra] : | :
| | : ,---' :
[Rc] +---:--/ \ :
| | : --+-- :
| [Rb] :...|...:
| | |
| `-------+
| |
- --+-----------'

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.
 
W

Winfield Hill

Jan 1, 1970
0
Jim said:
Use something like a TL431 or its CMOS equivalent,
and get it dead-nuts-on.

I have to question why an old guy would use the
phrase "dead-nuts"?
 
R

Rich Grise

Jan 1, 1970
0
I have to question why an old guy would use the phrase "dead-nuts"?

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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