Bought a rather nice small LED voltmeter off Ebay for not a lot. It's a 3
digit type. For the old Rover which didn't have any battery indication -
intend fitting it in the middle of the rev-counter face. However, it's a
bit bright for night time. Any clues about dimming it? Can't get a data
sheet for it - came from the far east.
The PCB has a single processor and two regulators - one 5 volt and one
3.3v. I'd guess the latter is for the display. But being surface mount,
rather difficult to suss out the schematic.

--
*That's it! I‘m calling grandma!

Dave Plowman London SW
To e-mail, change noise into sound.

On 22/08/11 16:16, Dave Plowman (News) wrote:
Bought a rather nice small LED voltmeter off Ebay for not a lot. It's a 3
digit type. For the old Rover which didn't have any battery indication -
intend fitting it in the middle of the rev-counter face. However, it's a
bit bright for night time. Any clues about dimming it? Can't get a data
sheet for it - came from the far east.

Sweet wrapper stuck over the display.


--
Bernard Peek

On Mon, 22 Aug 2011 16:16:38 +0100, "Dave Plowman (News)"
wrote:

Bought a rather nice small LED voltmeter off Ebay for not a lot. It's a 3
digit type. For the old Rover which didn't have any battery indication -
intend fitting it in the middle of the rev-counter face. However, it's a
bit bright for night time. Any clues about dimming it? Can't get a data
sheet for it - came from the far east.
The PCB has a single processor and two regulators - one 5 volt and one
3.3v. I'd guess the latter is for the display. But being surface mount,
rather difficult to suss out the schematic.

A bit of neutral density filter material - or even colour gel to suit
the car interior!

--
Frank Erskine

On Aug 22, 4:16*pm, "Dave Plowman (News)"
wrote:
The PCB has a single processor and two regulators *- one 5 volt and one
3.3v. I'd guess the latter is for the display. But being surface mount,
rather difficult to suss out the schematic.

Suss out the schematic. You probably only need to find a chip number,
then search for a datasheet. This should give you (if it's easy) the
identity of the brightness control pin, then you probably need to up a
resistor value supplying it.

In extremis, look for mid-range resistors supply an IC pin from Vcc,
with no other connections, then experiment.

Bernard Peek wrote:
On 22/08/11 16:16, Dave Plowman (News) wrote:
Bought a rather nice small LED voltmeter off Ebay for not a lot. It's a 3
digit type. For the old Rover which didn't have any battery indication -
intend fitting it in the middle of the rev-counter face. However, it's a
bit bright for night time. Any clues about dimming it? Can't get a data
sheet for it - came from the far east.

Sweet wrapper stuck over the display.

Well, I was going to suggest some neutral density filter material ...

On 22/08/2011 18:08, Andy Burns wrote:
Bernard Peek wrote:
On 22/08/11 16:16, Dave Plowman (News) wrote:
Bought a rather nice small LED voltmeter off Ebay for not a lot. It's
a 3
digit type. For the old Rover which didn't have any battery indication -
intend fitting it in the middle of the rev-counter face. However, it's a
bit bright for night time. Any clues about dimming it? Can't get a data
sheet for it - came from the far east.

Sweet wrapper stuck over the display.

Well, I was going to suggest some neutral density filter material ...


But I imagine that the brightness needs to be switchable - maybe going
to the lower level when the car lights are switched on.
--
Cheers,
Roger
____________
Please reply to Newsgroup. Whilst email address is valid, it is seldom
checked.

In article , Andy Burns
wrote:
Bernard Peek wrote:
On 22/08/11 16:16, Dave Plowman (News) wrote:
Bought a rather nice small LED voltmeter off Ebay for not a lot. It's
a 3 digit type. For the old Rover which didn't have any battery
indication - intend fitting it in the middle of the rev-counter face.
However, it's a bit bright for night time. Any clues about dimming
it? Can't get a data sheet for it - came from the far east.

Sweet wrapper stuck over the display.

Well, I was going to suggest some neutral density filter material ...

Should have said its fine in daylight. Only too bright at night.

--
*Some people are only alive because it is illegal to kill.

Dave Plowman London SW
To e-mail, change noise into sound.

In article ,
Roger Mills wrote:
On 22/08/2011 18:08, Andy Burns wrote:
Bernard Peek wrote:
On 22/08/11 16:16, Dave Plowman (News) wrote:
Bought a rather nice small LED voltmeter off Ebay for not a lot.
It's a 3 digit type. For the old Rover which didn't have any battery
indication - intend fitting it in the middle of the rev-counter
face. However, it's a bit bright for night time. Any clues about
dimming it? Can't get a data sheet for it - came from the far east.

Sweet wrapper stuck over the display.

Well, I was going to suggest some neutral density filter material ...


But I imagine that the brightness needs to be switchable - maybe going
to the lower level when the car lights are switched on.

In one.

--
*Stable Relationships Are For Horses.

Dave Plowman London SW
To e-mail, change noise into sound.

In article
,
Andy Dingley wrote:
Suss out the schematic. You probably only need to find a chip number,
then search for a datasheet.

Tried that - no joy. The PCB is marked JuYing.Ele.cn. ;-) The IC PHL 044.
Can't find anything on that unlike the voltage regs.

This should give you (if it's easy) the
identity of the brightness control pin, then you probably need to up a
resistor value supplying it.

--
*Don't byte off more than you can view *

Dave Plowman London SW
To e-mail, change noise into sound.

On Aug 22, 6:38*pm, "Dave Plowman (News)"
wrote:
In article
,
* *Andy Dingley wrote:

Suss out the schematic. You probably only need to find a chip number,
then search for a datasheet.

Tried that - no joy. The PCB is marked JuYing.Ele.cn. ;-) The IC PHL 044.
Can't find anything on that unlike the voltage regs.

This should give you (if it's easy) the
identity of the brightness control pin, then you probably need to up a
resistor value supplying it.

I'd run it from a current limited supply, connect a probe to ground
via a 10k resistor, and prod around the circuit. Somewhere it will
alter the brightness, failry likely.


NT

On 22/08/2011 16:16, Dave Plowman (News) wrote:
Bought a rather nice small LED voltmeter off Ebay for not a lot. It's a 3
digit type. For the old Rover which didn't have any battery indication -
intend fitting it in the middle of the rev-counter face. However, it's a
bit bright for night time. Any clues about dimming it? Can't get a data
sheet for it - came from the far east.
The PCB has a single processor and two regulators - one 5 volt and one
3.3v. I'd guess the latter is for the display. But being surface mount,
rather difficult to suss out the schematic.


LEDs normally have series resistors to limit the current, ( otherwise,
they represent almost a short-circuit in the forward direction! ) and
this controlls the brightness.

There may be a resistor bank somewhere near the displays.

THe current in the LEDs will be (supply voltage - 0.7 )/R
So dropping the voltage will also dim the displays.

However, that assumes that the displays have their own supply which does
not also supply ICs. If you drop the voltage to the ICs, then it will
stop working.

3.3 may well be the the IC supply, and the 5v for the display. You'd
need to trace it out on the PCB. If one supply does indeed supply the
displays only, then yes, you can rig up a dual-voltage arrangement, and
have the vehicle lighting toggle which voltage is used.

--
Ron

On Mon, 22 Aug 2011 16:16:38 +0100, "Dave Plowman (News)"
wrote:

Bought a rather nice small LED voltmeter off Ebay for not a lot. It's a 3
digit type. For the old Rover which didn't have any battery indication -
intend fitting it in the middle of the rev-counter face. However, it's a
bit bright for night time. Any clues about dimming it? Can't get a data
sheet for it - came from the far east.
The PCB has a single processor and two regulators - one 5 volt and one
3.3v. I'd guess the latter is for the display. But being surface mount,
rather difficult to suss out the schematic.

Do you really need an absolute value - not that long ago the LM3914
coupled with a few LED's was enough to satisfy the needs of endurance
racing at Le Mans. Dimming is easy to achieve, voltages above and
below normal can be made to flash the display.

Rather than use a 10 LED's you could even substitute a single multi
colour LED.


--

In article ,
Ron Lowe wrote:
LEDs normally have series resistors to limit the current, ( otherwise,
they represent almost a short-circuit in the forward direction! ) and
this controlls the brightness.

I do have a circuit for a similar device - a Vellerman LED voltmeter.
There are no external series resistors on that - just a driver chip. The
common anode on each display is fed via a transistor controlled again by
the driver.

There may be a resistor bank somewhere near the displays.

THe current in the LEDs will be (supply voltage - 0.7 )/R
So dropping the voltage will also dim the displays.

However, that assumes that the displays have their own supply which does
not also supply ICs. If you drop the voltage to the ICs, then it will
stop working.

3.3 may well be the the IC supply, and the 5v for the display. You'd
need to trace it out on the PCB. If one supply does indeed supply the
displays only, then yes, you can rig up a dual-voltage arrangement, and
have the vehicle lighting toggle which voltage is used.

The PCB is surface mount and fitted to the display. It is at least two
layers, so not possible to trace it out without removal.

There are very few external components. The 5 volt reg is much smaller
than the 3.3v one, so my guess is 5 volts for the IC, 3.3 for the display.
Since it's a blue display, 3.3 could be used to drive it with no current
limiting resistors?

My thought are to replace the 3.3 reg with a variable one and try a lower
voltage? There's plenty space to add an extra PCB in this installation.

Unless anyone has a better idea?

--
*Don't squat with your spurs on *

Dave Plowman London SW
To e-mail, change noise into sound.

The Other Mike wrote:
On Mon, 22 Aug 2011 16:16:38 +0100, "Dave Plowman (News)"
wrote:

Bought a rather nice small LED voltmeter off Ebay for not a lot. It's a 3
digit type. For the old Rover which didn't have any battery indication -
intend fitting it in the middle of the rev-counter face. However, it's a
bit bright for night time. Any clues about dimming it? Can't get a data
sheet for it - came from the far east.
The PCB has a single processor and two regulators - one 5 volt and one
3.3v. I'd guess the latter is for the display. But being surface mount,
rather difficult to suss out the schematic.

Do you really need an absolute value - not that long ago the LM3914
coupled with a few LED's was enough to satisfy the needs of endurance
racing at Le Mans. Dimming is easy to achieve, voltages above and
below normal can be made to flash the display.

Rather than use a 10 LED's you could even substitute a single multi
colour LED.


For that matter, I recently bought a dual output power socket for about
a tenner with an LCD DVM built into it. The power supply I use for the
netbook has a backlit one built in, and that was only about twenty quid.

Not much help to the OP, though, as he wants to use what he has.

--
Tciao for Now!

John.

In article ,
The Other Mike wrote:
Do you really need an absolute value - not that long ago the LM3914
coupled with a few LED's was enough to satisfy the needs of endurance
racing at Le Mans. Dimming is easy to achieve, voltages above and
below normal can be made to flash the display.

I'm not racing at Le Mans. ;-) An accurate voltage readout tells you about
the state of several things. Battery condition with the engine stopped,
charging system when running.

Rather than use a 10 LED's you could even substitute a single multi
colour LED.

Ages ago I fitted a current measuring system with a an LED which is green
on charge, red on discharge and amber when balancing the load. Which is ok
as an idiot light, but not so nice as a voltmeter.

--
*Oh, what a tangled website we weave when first we practice *

Dave Plowman London SW
To e-mail, change noise into sound.

In article ,
John Williamson wrote:
For that matter, I recently bought a dual output power socket for about
a tenner with an LCD DVM built into it. The power supply I use for the
netbook has a backlit one built in, and that was only about twenty quid.

Not much help to the OP, though, as he wants to use what he has.

There are some gotchas with these meters. Not all can be used to measure
the voltage of their own power supply - like a car battery.
There are small LCD units which can - but I couldn't find one with
illumination.

It's to be fitted in the analogue rev counter dial. The numbers on that
are approx 5mm in height. The LED display I'm using, 10mm. Most are a
great deal bigger.

--
*Puritanism: The haunting fear that someone, somewhere may be happy.

Dave Plowman London SW
To e-mail, change noise into sound.

On Mon, 22 Aug 2011 16:16:38 +0100, Dave Plowman (News) wrote:

Bought a rather nice small LED voltmeter off Ebay for not a lot. It's a
3 digit type. For the old Rover which didn't have any battery indication
- intend fitting it in the middle of the rev-counter face. However, it's
a bit bright for night time. Any clues about dimming it? Can't get a
data sheet for it - came from the far east. The PCB has a single
processor and two regulators - one 5 volt and one 3.3v. I'd guess the
latter is for the display. But being surface mount, rather difficult to
suss out the schematic.

How are the LED segments driven? 3-digit is 21 segments (ignoring DP) -
are each of those controlled by a single pin on the IC?

On Aug 23, 1:26*pm, "Dave Plowman (News)"
wrote:
There are some gotchas with these meters. Not all can be used to measure
the voltage of their own power supply - like a car battery.

Course they can - you drop the supply voltage with a big linear reg to
5v or 3.3v as needed and you divide the measured voltage down to about
half of this. They'll thus work quite happily, as you're not trying to
measure a voltage anywhere near the supply rail voltage, and you've a
stable voltage to drive the meter circuit. If the battery voltage
drops too low to drive the meter chip (on the far side of a linear
that's expecting to be halving it), then your battery is flat and
you've probably noticed this by now.

Otherwise just rewire your car with a commercial DC-DC module inside
the dash and have cleaned-up 12V & 5V supply rails available to feed
anything you hang in there. My MG's dashboard even has a crankcase
accelerometer to tell me to back off from breaking the crankshaft -
output is a brown-backlit LCD text display which just looks like a bit
of art deco bakelite when the power is off.

In article
,
Andy Dingley wrote:
There are some gotchas with these meters. Not all can be used to measure
the voltage of their own power supply - like a car battery.

Course they can - you drop the supply voltage with a big linear reg to
5v or 3.3v as needed and you divide the measured voltage down to about
half of this. They'll thus work quite happily, as you're not trying to
measure a voltage anywhere near the supply rail voltage, and you've a
stable voltage to drive the meter circuit. If the battery voltage
drops too low to drive the meter chip (on the far side of a linear
that's expecting to be halving it), then your battery is flat and
you've probably noticed this by now.

It's more to do with the input to the module, IIRC. Some certainly say
they aren't suitable for measuring their own supply.

Otherwise just rewire your car with a commercial DC-DC module inside
the dash and have cleaned-up 12V & 5V supply rails available to feed
anything you hang in there. My MG's dashboard even has a crankcase
accelerometer to tell me to back off from breaking the crankshaft -
output is a brown-backlit LCD text display which just looks like a bit
of art deco bakelite when the power is off.

But there's no need for any of this with the cheap unit I've bought. It
works straight out of the box. All I need to do is find a way of dimming
the LEDs when the car lights are on, at night. ;-)

--
*Be more or less specific *

Dave Plowman London SW
To e-mail, change noise into sound.

Jules Richardson wrote:
On Mon, 22 Aug 2011 16:16:38 +0100, Dave Plowman (News) wrote:

Bought a rather nice small LED voltmeter off Ebay for not a lot. It's a
3 digit type. For the old Rover which didn't have any battery indication
- intend fitting it in the middle of the rev-counter face. However, it's
a bit bright for night time. Any clues about dimming it? Can't get a
data sheet for it - came from the far east. The PCB has a single
processor and two regulators - one 5 volt and one 3.3v. I'd guess the
latter is for the display. But being surface mount, rather difficult to
suss out the schematic.

How are the LED segments driven? 3-digit is 21 segments (ignoring DP) -
are each of those controlled by a single pin on the IC?

Most LED displays are multiplex driven 7 or 8 rows x 3 columns and are
bit of a pig to dim unless the driver has a pulse width modulator
built-in which many do. Single resistor pull up or down usually sets
brightness. With no data on the chip then careful probing with a 10k
resistor is possibly the way to investigate.

Bob

On Tue, 23 Aug 2011 16:05:05 +0100, Bob Minchin wrote:

Jules Richardson wrote:
On Mon, 22 Aug 2011 16:16:38 +0100, Dave Plowman (News) wrote:

Bought a rather nice small LED voltmeter off Ebay for not a lot. It's
a 3 digit type. For the old Rover which didn't have any battery
indication - intend fitting it in the middle of the rev-counter face.
However, it's a bit bright for night time. Any clues about dimming it?
Can't get a data sheet for it - came from the far east. The PCB has a
single processor and two regulators - one 5 volt and one 3.3v. I'd
guess the latter is for the display. But being surface mount, rather
difficult to suss out the schematic.

How are the LED segments driven? 3-digit is 21 segments (ignoring DP) -
are each of those controlled by a single pin on the IC?

Most LED displays are multiplex driven 7 or 8 rows x 3 columns

Yep - that's why I was checking, as the OP gave the impression that the
board just had the LEDs, main IC, and a couple of voltage regulators. I'm
surprised* that it doesn't have any resistors between the segments and
the control chip's outputs, and perhaps a trio of transistors used for
multiplexing.

* but maybe it really is a "voltmeter on a chip" and so everything's
built-in :-(

cheers

Jules

Jules Richardson wrote:
On Tue, 23 Aug 2011 16:05:05 +0100, Bob Minchin wrote:

Jules Richardson wrote:
On Mon, 22 Aug 2011 16:16:38 +0100, Dave Plowman (News) wrote:

Bought a rather nice small LED voltmeter off Ebay for not a lot. It's
a 3 digit type. For the old Rover which didn't have any battery
indication - intend fitting it in the middle of the rev-counter face.
However, it's a bit bright for night time. Any clues about dimming it?
Can't get a data sheet for it - came from the far east. The PCB has a
single processor and two regulators - one 5 volt and one 3.3v. I'd
guess the latter is for the display. But being surface mount, rather
difficult to suss out the schematic.

How are the LED segments driven? 3-digit is 21 segments (ignoring DP) -
are each of those controlled by a single pin on the IC?

Most LED displays are multiplex driven 7 or 8 rows x 3 columns

Yep - that's why I was checking, as the OP gave the impression that the
board just had the LEDs, main IC, and a couple of voltage regulators. I'm
surprised* that it doesn't have any resistors between the segments and
the control chip's outputs, and perhaps a trio of transistors used for
multiplexing.

* but maybe it really is a "voltmeter on a chip" and so everything's
built-in :-(

cheers

Jules

It could even be a PIC type processor but that might be too costly even
if a masked programmed version. Only bonus for a high volume chip would
be things like brightness control would be included.

Bob

Bob Minchin wrote:
Jules Richardson wrote:
On Tue, 23 Aug 2011 16:05:05 +0100, Bob Minchin wrote:

Jules Richardson wrote:
On Mon, 22 Aug 2011 16:16:38 +0100, Dave Plowman (News) wrote:

Bought a rather nice small LED voltmeter off Ebay for not a lot. It's
a 3 digit type. For the old Rover which didn't have any battery
indication - intend fitting it in the middle of the rev-counter face.
However, it's a bit bright for night time. Any clues about dimming it?
Can't get a data sheet for it - came from the far east. The PCB has a
single processor and two regulators - one 5 volt and one 3.3v. I'd
guess the latter is for the display. But being surface mount, rather
difficult to suss out the schematic.

How are the LED segments driven? 3-digit is 21 segments (ignoring DP) -
are each of those controlled by a single pin on the IC?

Most LED displays are multiplex driven 7 or 8 rows x 3 columns

Yep - that's why I was checking, as the OP gave the impression that the
board just had the LEDs, main IC, and a couple of voltage regulators. I'm
surprised* that it doesn't have any resistors between the segments and
the control chip's outputs, and perhaps a trio of transistors used for
multiplexing.

* but maybe it really is a "voltmeter on a chip" and so everything's
built-in :-(

cheers

Jules

It could even be a PIC type processor but that might be too costly even
if a masked programmed version. Only bonus for a high volume chip would
be things like brightness control would be included.

Like this one?

http://tuxgraphics.org/electronics/2...oltmeter.shtml

--
Tciao for Now!

John.

In article ,
John Williamson wrote:
It could even be a PIC type processor but that might be too costly
even if a masked programmed version. Only bonus for a high volume
chip would be things like brightness control would be included.

Like this one?

http://tuxgraphics.org/electronics/2...oltmeter.shtml

That clearly states the problem I found - many commercial units can't
measure their own power supply.

--
*Suicidal twin kills sister by mistake.

Dave Plowman London SW
To e-mail, change noise into sound.

Dave Plowman (News) wrote:
In article ,
John Williamson wrote:
It could even be a PIC type processor but that might be too costly
even if a masked programmed version. Only bonus for a high volume
chip would be things like brightness control would be included.

Like this one?

http://tuxgraphics.org/electronics/2...oltmeter.shtml

That clearly states the problem I found - many commercial units can't
measure their own power supply.

I was thinking more of the kit that can allegedly be supplied via that
page, which can. Although, if an extra component can be tolerated, an
isolating DC-DC converter for the DVM supply isn't expensive.

http://www.maplin.co.uk/1w-single-ou...rdercode=N83CN

For instance,

--
Tciao for Now!

John.

Dave Plowman (News) wrote:
In article ,
John Williamson wrote:
It could even be a PIC type processor but that might be too costly
even if a masked programmed version. Only bonus for a high volume
chip would be things like brightness control would be included.

Like this one?

http://tuxgraphics.org/electronics/2...oltmeter.shtml

That clearly states the problem I found - many commercial units can't
measure their own power supply.

That is usually a matter of a little analogue circuitry

In article ,
The Natural Philosopher wrote:
Dave Plowman (News) wrote:
In article ,
John Williamson wrote:
It could even be a PIC type processor but that might be too costly
even if a masked programmed version. Only bonus for a high volume
chip would be things like brightness control would be included.

Like this one?

http://tuxgraphics.org/electronics/2...oltmeter.shtml

That clearly states the problem I found - many commercial units can't
measure their own power supply.

That is usually a matter of a little analogue circuitry

Easier to simply buy one which can. There's a big range out there in the
more usual display sizes. In my case, the requirement was for a much
smaller one than you'd probably want for other uses. And luckily is
designed for the job I wanted it for.

--
*A clear conscience is the sign of a fuzzy memory.

Dave Plowman London SW
To e-mail, change noise into sound.

On Aug 24, 12:28*am, "Dave Plowman (News)"
wrote:
That clearly states the problem I found - many commercial units can't
measure their own power supply.

Two resistors fixes that.

Dave Plowman (News) wrote:
In article ,
The Natural Philosopher wrote:
Dave Plowman (News) wrote:
In article ,
John Williamson wrote:
It could even be a PIC type processor but that might be too costly
even if a masked programmed version. Only bonus for a high volume
chip would be things like brightness control would be included.

Like this one?
http://tuxgraphics.org/electronics/2...oltmeter.shtml
That clearly states the problem I found - many commercial units can't
measure their own power supply.

That is usually a matter of a little analogue circuitry

Easier to simply buy one which can. There's a big range out there in the
more usual display sizes. In my case, the requirement was for a much
smaller one than you'd probably want for other uses. And luckily is
designed for the job I wanted it for.

So the problem is electrically dimming it yes?

And you don't know how the backlighter is driven?

Ive forgotten..was it LED or LCD?