# Assembling a digital voltage display

J

#### JoeSpareBedroom

Jan 1, 1970
0
I need to assemble a digital voltage display for, of all things, a bass
guitar which uses two 9v batteries to supply power for tone control
circuitry. I need some tips. The problem to be solved is this: Unscrewing
the battery hatch in the instrument is no big deal, but checking the
batteries involves flexing the wires, and this has caused failures twice in
the past. So, I'm thinking of mounting something like this on the surface of
the instrument:

http://tinyurl.com/2yt6mx

I'd actually need a display which also showed a decimal point and tenths of
volts, but the example should be enough to illustrate the basic idea here.
In addition to the display, I'll probablly want to mount a button or switch
to disconnect the batteries from the circuitry, and enable the display just
long enough to check voltage. I need to measure as low as about 6.5 volts,
at which point the circuitry ceases to operate, and any lower voltage is
irrelevant.

So:

1) If components like the LED display could operate without a few other
parts involved, that would be too easy, right? If someone can recommend a
decent book which might contain info on what I'd need to add, in order to
make this work, that would be great. (I'm old - I know how to operate a
library card).

2) I haven't checked all 28 billion google results yet, but if anyone can
suggest a better source than Radio Shack for LED displays, that would be
great.

Of course, I could just mount a banana plug jack on the face of the
instrument, and plug in a voltmeter when necessary, but that's one more
contraption I don't have room for on top of the amp during performances.

T

#### Tim

Jan 1, 1970
0
I need to assemble a digital voltage display for, of all things, a bass
guitar which uses two 9v batteries to supply power for tone control
circuitry. I need some tips. The problem to be solved is this: Unscrewing
the battery hatch in the instrument is no big deal, but checking the
batteries involves flexing the wires, and this has caused failures twice in
the past. So, I'm thinking of mounting something like this on the surface of
the instrument:

http://tinyurl.com/2yt6mx

I'd actually need a display which also showed a decimal point and tenths of
volts, but the example should be enough to illustrate the basic idea here.
In addition to the display, I'll probablly want to mount a button or switch
to disconnect the batteries from the circuitry, and enable the display just
long enough to check voltage. I need to measure as low as about 6.5 volts,
at which point the circuitry ceases to operate, and any lower voltage is
irrelevant.

So:

1) If components like the LED display could operate without a few other
parts involved, that would be too easy, right? If someone can recommend a
decent book which might contain info on what I'd need to add, in order to
make this work, that would be great. (I'm old - I know how to operate a
library card).

2) I haven't checked all 28 billion google results yet, but if anyone can
suggest a better source than Radio Shack for LED displays, that would be
great.

Of course, I could just mount a banana plug jack on the face of the
instrument, and plug in a voltmeter when necessary, but that's one more
contraption I don't have room for on top of the amp during performances.
Any device you put on to monitor your batteries is going cause more
drain. Instead of LED type, you might want to consider LCD, or perhaps a
low battery warning with no display, something that beeps when you need
to replace the cells.

My 2 cents worth anyways... (and that's CDN cents too...)

- Tim -

J

#### JoeSpareBedroom

Jan 1, 1970
0
Tim said:
Any device you put on to monitor your batteries is going cause more
drain. Instead of LED type, you might want to consider LCD, or perhaps a
low battery warning with no display, something that beeps when you need
to replace the cells.

My 2 cents worth anyways... (and that's CDN cents too...)

- Tim -

LCD would be fine. A bit less visible, but not a big problem. As far as the
beep idea, it would never be heard during a performance.

T

#### Tim

Jan 1, 1970
0
LCD would be fine. A bit less visible, but not a big problem. As far as the
beep idea, it would never be heard during a performance.
Well my idea of a low battery warning, would be at the point where you
would have less than a few hours left on cells, not when you had a few
minutes, so if you had a beep before the set, you changed batteries. A
beep after or during the set would not be a concern, as you would have
enough power to finish the set.

- Tim -

E

#### ehsjr

Jan 1, 1970
0
JoeSpareBedroom said:
Of course, I could just mount a banana plug jack on the face of the
instrument, and plug in a voltmeter when necessary, but that's one more
contraption I don't have room for on top of the amp during performances.

That's your best option. Get some Velcro with
adhesive backing, and hang the voltmeter on the
side of the amp.You can get a dirt cheap voltmeter
on sale from Harbor Freight that will be fine for
this function. It's on sale now for $4.99 - in the past it has gone for as low as$2.99. ITEM 90899-2VGA
http://www.harborfreight.com/

Ed

A

#### [email protected]

Jan 1, 1970
0
Why so complicated? Why not a good old d'Arsonval movement? Drains
microamps.

J

#### JoeSpareBedroom

Jan 1, 1970
0
Why so complicated? Why not a good old d'Arsonval movement? Drains
microamps.

Needle type meter? I wondered about that, but I also wonder about
durability. The bass doesn't get banged around much, but still....

And on the other hand, I've met old Simpson meters that never seem to die.

G

#### Gary Tait

Jan 1, 1970
0
LCD would be fine. A bit less visible, but not a big problem. As far
as the beep idea, it would never be heard during a performance.

If you want a small battery level meter, a simple bar meter will do (button
activated) , or even a simple comparater lighting a "battery good" LED, or
a "battery low" LED

You could esaily attach a coaxial jack on each device you wish to test, and
use an external tester that would be no bigger than a 9V battery.

L

#### Lostgallifreyan

Jan 1, 1970
0
or even a simple comparater lighting a "battery good" LED, or
a "battery low" LED

I was thinking this too. Never came up with the goods though so I let it
go... I was thinking of MOSFETS. There might be a way to keep one turned
off when the gate voltage is high enough, so that the total current draw is
in the nanoamp range, but the LED begins to glow more as voltage falls.
Obviously the limited remaining charge will be used even more rapidly, but
usefully, and no significant drain would begin till there was a need to
indicate. I'd hoped to work out something with one FET, an LED, and no more
than two resistors, but it eluded me. Maybe it can't be done that simply,
but it seems like the way to go, to get as close to that as possible.

R

#### rpbc

Jan 1, 1970
0
by "JoeSpareBedroom" <[email protected][EMAIL PROTECTED] > May 5, 2007 at 03:16
PM

<[email protected][EMAIL PROTECTED]
wrote in message
Why so complicated? Why not a good old d'Arsonval movement? Drains
microamps.

Needle type meter? I wondered about that, but I also wonder about
durability. The bass doesn't get banged around much, but still....

And on the other hand, I've met old Simpson meters that never seem to
die.

rpbc: Why not build a regulated 9 volt supply and feed it from the power
supply of the bass amp... or just buy a little wall type transformer of
the right voltage wired to the bass amp power switch, and add filter and
regulation to that? Then you won't have to worry about the battery.

J

#### JoeSpareBedroom

Jan 1, 1970
0
rpbc said:
by "JoeSpareBedroom" <[email protected][EMAIL PROTECTED] > May 5, 2007 at
03:16
PM

<[email protected][EMAIL PROTECTED]
wrote in message
Why so complicated? Why not a good old d'Arsonval movement? Drains
microamps.

Needle type meter? I wondered about that, but I also wonder about
durability. The bass doesn't get banged around much, but still....

And on the other hand, I've met old Simpson meters that never seem to
die.

rpbc: Why not build a regulated 9 volt supply and feed it from the power
supply of the bass amp... or just buy a little wall type transformer of
the right voltage wired to the bass amp power switch, and add filter and
regulation to that? Then you won't have to worry about the battery.

Because I play 99% of the time with a Sennheiser wireless setup. I move
around too much to have wires underfoot.

R

#### rpbc

Jan 1, 1970
0
by "JoeSpareBedroom" <[email protected][EMAIL PROTECTED] > May 12, 2007 at
09:36 PM

"rpbc" <[email protected][EMAIL PROTECTED]
.com> wrote in message
by "JoeSpareBedroom" <[email protected][EMAIL PROTECTED] PROTECTED] > May 5, 2007 at
03:16
PM

<[email protected][EMAIL PROTECTED] PROTECTED]
wrote in message
Why so complicated? Why not a good old d'Arsonval movement? Drains
microamps.

Needle type meter? I wondered about that, but I also wonder about
durability. The bass doesn't get banged around much, but still....

And on the other hand, I've met old Simpson meters that never seem to
die.

rpbc: Why not build a regulated 9 volt supply and feed it from the power
supply of the bass amp... or just buy a little wall type transformer of
the right voltage wired to the bass amp power switch, and add filter and
regulation to that? Then you won't have to worry about the battery.

Because I play 99% of the time with a Sennheiser wireless setup. I move
around too much to have wires underfoot.

rpbc: Oh, I see. Think I only got half the picture. Could you install a
little female jack on the compartment wired to the battery and have a male
plug on the leads of a voltmeter so you can just plug in an measure? You
could measure with the unit on so the reading will be under load.

J

#### JoeSpareBedroom

Jan 1, 1970
0
rpbc said:
by "JoeSpareBedroom" <[email protected][EMAIL PROTECTED] > May 12, 2007 at
09:36 PM

"rpbc" <[email protected][EMAIL PROTECTED]
.com> wrote in message
by "JoeSpareBedroom" <[email protected][EMAIL PROTECTED] PROTECTED] > May 5, 2007 at
03:16
PM

<[email protected][EMAIL PROTECTED] PROTECTED]
wrote in message
Why so complicated? Why not a good old d'Arsonval movement? Drains
microamps.

Needle type meter? I wondered about that, but I also wonder about
durability. The bass doesn't get banged around much, but still....

And on the other hand, I've met old Simpson meters that never seem to
die.

rpbc: Why not build a regulated 9 volt supply and feed it from the power
supply of the bass amp... or just buy a little wall type transformer of
the right voltage wired to the bass amp power switch, and add filter and
regulation to that? Then you won't have to worry about the battery.

Because I play 99% of the time with a Sennheiser wireless setup. I move
around too much to have wires underfoot.

rpbc: Oh, I see. Think I only got half the picture. Could you install a
little female jack on the compartment wired to the battery and have a male
plug on the leads of a voltmeter so you can just plug in an measure? You
could measure with the unit on so the reading will be under load.

That's the solution I'm leaning toward right now. The compartment is
precisely big enough for the two 9v batteries. I'm taking the bass to a
luthier later this week to discuss the safest direction in which to rout out
enough space for a banana jack, without threatening the integrity of the
wooden body.

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