Digital panel meters with VCC < 5V?

[Joerg]

Hello Folks,

Just happened again: A design needs a digital panel meter to display a
voltage. Something in the usual $35 range. Problem is that Vbat must be
allowed to drop to 5V or a tad less and that is also the supply of the
usual panel meter. They seem to come only in 5V, 9V and 4-20mA loop for
their supply. The loop versions cost a lot more. Sure, I could generate
5V, 9V or whatever but it's a hassle.

Is there any mainstream (non-expensive) digital panel meter that can
live with less than 5V? I mean, there are plenty of handheld meters out
there that use a couple AA cells. It just wouldn't be practical to
disect these and try to mount them into bezels or cutouts.

Regards, Joerg

 

[Frank Bemelman]

Hello Folks,

Just happened again: A design needs a digital panel meter to display a
voltage. Something in the usual $35 range. Problem is that Vbat must be
allowed to drop to 5V or a tad less and that is also the supply of the
usual panel meter. They seem to come only in 5V, 9V and 4-20mA loop for
their supply. The loop versions cost a lot more. Sure, I could generate
5V, 9V or whatever but it's a hassle.

I suppose if a panel meter is rated for 5V it may work too with 4V. But
you need to try and find out.

Is there any mainstream (non-expensive) digital panel meter that can
live with less than 5V? I mean, there are plenty of handheld meters out
there that use a couple AA cells. It just wouldn't be practical to
disect these and try to mount them into bezels or cutouts.

Not very practical indeed. You'd also need to check if the test lead
and negative battery terminal share a common ground.

 

[colin]

Hello Folks,

Just happened again: A design needs a digital panel meter to display a
voltage. Something in the usual $35 range. Problem is that Vbat must be
allowed to drop to 5V or a tad less and that is also the supply of the
usual panel meter. They seem to come only in 5V, 9V and 4-20mA loop for
their supply. The loop versions cost a lot more. Sure, I could generate
5V, 9V or whatever but it's a hassle.

Is there any mainstream (non-expensive) digital panel meter that can
live with less than 5V? I mean, there are plenty of handheld meters out
there that use a couple AA cells. It just wouldn't be practical to
disect these and try to mount them into bezels or cutouts.

Regards, Joerg

The Vbat low seems tantalizingly close enough does it need to be regulated
tho ?
if so would an ultro low dropout regulator do (100mv) ? the meter 5v must
have a +-10% on its spec at least.

Colin =^.^=

 

[Joerg]

Hello Colin,

The Vbat low seems tantalizingly close enough does it need to be regulated
tho ?
if so would an ultro low dropout regulator do (100mv) ? the meter 5v must
have a +-10% on its spec at least.

An LDO is what I will use if I must accept a 5V meter. But LDOs aren't
the most stable circuits so I'd rather not if I can avoid them. They are
often fickle when it comes to source impedance.

Specsmanship for many meters leaves something to be desired. Often there
isn't any spec for VCC tolerance on the usual two-page pdf. Then you
have to contact the source, hoping it isn't just some sales outlet.

Regards, Joerg

 

[Joerg]

Hello Frank,

Not very practical indeed. You'd also need to check if the test lead
and negative battery terminal share a common ground.

They do for many of the 5V versions. That is ok in this case.

Regards, Joerg

 

[colin]

Hello Colin,


An LDO is what I will use if I must accept a 5V meter. But LDOs aren't
the most stable circuits so I'd rather not if I can avoid them. They are
often fickle when it comes to source impedance.

Specsmanship for many meters leaves something to be desired. Often there
isn't any spec for VCC tolerance on the usual two-page pdf. Then you
have to contact the source, hoping it isn't just some sales outlet.

Regards, Joerg

I had a similar problem once, needed to power a 68hc11 in a handheld unit,
but the power requirment went up so needed larger bateries wich meant I cld
only fit 4 Nicads instead of the 6 smaller ones I planned, I managed to get
away with it but had to use a p-ch mosfet and op amp as an alomst zero drop
regulator, good luck. Ive used LDOs but at low currents where they are more
stable. is this an LED meter ?

Colin =^.^=

 

[Winfield Hill]

Joerg wrote...

Specsmanship for many meters leaves something to be desired. Often there
isn't any spec for VCC tolerance on the usual two-page pdf. Then you
have to contact the source, hoping it isn't just some sales outlet.

I like the Datel meters (now they've thrown away the decades of brand
recognition and are called C&D Technologies Power Electronics Division
or something). They specify the +5 supply as 4.75 to 5.25 volts, but
from the architecture one knows they'll no doubt work without accuracy
degradation at lower voltages. The low-power LCD versions, like the
DMS-30LCD-1-9, which draws 350uA from 9V batteries, are specified with
a 7.5 to 14-volt range, but again one wonders about that 7.5V number.
http://www.datel.com/data/meters/30lcd.pdf

 

[Joerg]

Hello Winfield,

I like the Datel meters (now they've thrown away the decades of brand
recognition and are called C&D Technologies Power Electronics Division
or something). They specify the +5 supply as 4.75 to 5.25 volts, but
from the architecture one knows they'll no doubt work without accuracy
degradation at lower voltages. The low-power LCD versions, like the
DMS-30LCD-1-9, which draws 350uA from 9V batteries, are specified with
a 7.5 to 14-volt range, but again one wonders about that 7.5V number.
http://www.datel.com/data/meters/30lcd.pdf

Thanks. These are nice. The only downside is that these seem to be in
the $50 class. Mouser has quite a few of them.

Regards, Joerg

 

[Joerg]

Hello Colin,

I had a similar problem once, needed to power a 68hc11 in a handheld unit,
but the power requirment went up so needed larger bateries wich meant I cld
only fit 4 Nicads instead of the 6 smaller ones I planned, I managed to get
away with it but had to use a p-ch mosfet and op amp as an alomst zero drop
regulator, good luck. Ive used LDOs but at low currents where they are more
stable. is this an LED meter ?

Yes, those last minute spec changes. I try not to get grumpy when that
happens but see it as a challenge.

This would be an LCD meter, non-backlit. LED consumes too much. However,
the 5V versions consume much more than the same meter in 9V. Guess they
just roach on a converter. If we could obtain the schematic this would
all be a cake walk. But mostly they don't disclose that.

Regards, Joerg

 

[Joerg]

Hello Jamie,

go there, they have a whole list of panel
meters LCD/LED in the 5 to 9 voltage range
using different configs in the range of
12.95 .. 16.00 bucks or so.

http://www.circuitspecialists.com/

Thanks. They do have good prices. Much better than Digikey and the other
big ones. The specs, ahem, I guess they took a digital camera and
photographed the single sheet that comes with the meter. But for test
rigs that may be ok.

Regards, Joerg

 

[Jamie]

Hello Winfield,



Thanks. These are nice. The only downside is that these seem to be in
the $50 class. Mouser has quite a few of them.

Regards, Joerg

go there, they have a whole list of panel
meters LCD/LED in the 5 to 9 voltage range
using different configs in the range of
12.95 .. 16.00 bucks or so.

http://www.circuitspecialists.com/

 

[Peter Bennett]

Hello Folks,

Just happened again: A design needs a digital panel meter to display a
voltage. Something in the usual $35 range. Problem is that Vbat must be
allowed to drop to 5V or a tad less and that is also the supply of the
usual panel meter. They seem to come only in 5V, 9V and 4-20mA loop for
their supply. The loop versions cost a lot more. Sure, I could generate
5V, 9V or whatever but it's a hassle.

Is there any mainstream (non-expensive) digital panel meter that can
live with less than 5V? I mean, there are plenty of handheld meters out
there that use a couple AA cells. It just wouldn't be practical to
disect these and try to mount them into bezels or cutouts.

Regards, Joerg

Try http://www.lascarelectronics.com/data/pdf/SP 200.pdf - the spec
sheet says the Vcc is 3.5 - 5.25 volts _and_ one side of the measured
voltage can be connected to the power supply ground (I've just bought
two of these from Newark, but haven't actually put them in service
yet...)(they are based on a Maxim MAX 138)



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Peter Bennett, VE7CEI
peterbb4 (at) interchange.ubc.ca
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[ehsjr]

Hello Folks,

Just happened again: A design needs a digital panel meter to display a
voltage. Something in the usual $35 range. Problem is that Vbat must be
allowed to drop to 5V or a tad less and that is also the supply of the
usual panel meter. They seem to come only in 5V, 9V and 4-20mA loop for
their supply. The loop versions cost a lot more. Sure, I could generate
5V, 9V or whatever but it's a hassle.

Is there any mainstream (non-expensive) digital panel meter that can
live with less than 5V? I mean, there are plenty of handheld meters out
there that use a couple AA cells. It just wouldn't be practical to
disect these and try to mount them into bezels or cutouts.

Regards, Joerg

I know you want to avoid the hassle of generating the voltage,
but you might want to re-think that, if you want a guaranteed
supply to the panel meter when the Vcc dips. I don't know
your Vcc range - only that it dips below 5V. With that in mind:
I've used a Tl499 boost converter/regulator down below 2 volts
to get a rock solid V out. The thing works on Vin from 1 to 10,
and has a resistor programmable Vout of 2.9 to 30, and provides
up to 100 mA. You need an inductor, 3 resistors and 2 caps. You
can set Vout to whatever V the dpm needs, allowing you to choose
the lower cost units.

Ed

 

[Rich Grise]

Hello Folks,

Just happened again: A design needs a digital panel meter to display a
voltage. Something in the usual $35 range. Problem is that Vbat must be
allowed to drop to 5V or a tad less and that is also the supply of the
usual panel meter. They seem to come only in 5V, 9V and 4-20mA loop for
their supply. The loop versions cost a lot more. Sure, I could generate
5V, 9V or whatever but it's a hassle.

Is there any mainstream (non-expensive) digital panel meter that can
live with less than 5V? I mean, there are plenty of handheld meters out
there that use a couple AA cells. It just wouldn't be practical to
disect these and try to mount them into bezels or cutouts.

Joerg? What are you leaving out here? You have a DPM application,
and you're afraid your 5V battery will droop below the +5V input
spec of your DPM?

There's something I'm missing here - or, Joerg, are you funning
with us? ;-P

Cheers!
Rich

 

[Joerg]

Hello Rich,

Joerg? What are you leaving out here? You have a DPM application,
and you're afraid your 5V battery will droop below the +5V input
spec of your DPM?

The rest of the system has a battery that can drop to 5V or a bit less.
So even an LDO would let go if I'd try to regulate to 5V. If the meter
could take 4.5V it would be fine.

Regards, Joerg

 

[Joerg]

Hello Peter,

Try http://www.lascarelectronics.com/data/pdf/SP 200.pdf - the spec
sheet says the Vcc is 3.5 - 5.25 volts _and_ one side of the measured
voltage can be connected to the power supply ground (I've just bought
two of these from Newark, but haven't actually put them in service
yet...)(they are based on a Maxim MAX 138)

Thanks. That's exactly what I was looking for. The SP200 has a backlight
which can't be used here but I bet it's readable without.

Regards, Joerg

 

[Joerg]

Hello Ed,

I know you want to avoid the hassle of generating the voltage,...
Yes.

...but you might want to re-think that, if you want a guaranteed
supply to the panel meter when the Vcc dips. ...

I might. But instead of the TL499 you can also use an inverter as an
oscillator, create twice VCC and regulate down. Maybe with a couple of
inverters to buffer for enough current but that won't be a big deal
since they come in a "six pack".

Regards, Joerg

 

[Peter Bennett]

Hello Peter,


Thanks. That's exactly what I was looking for. The SP200 has a backlight
which can't be used here but I bet it's readable without.

Yes - easily readable in normal room lighting without the backlight.

 

[Joerg]

Hello Peter,

Yes - easily readable in normal room lighting without the backlight.

Thanks, that is good to know. This isn't always the case. For example
the LCD display on the phone here in my office isn't readable until the
backlight comes on.

Regards, Joerg

 

[[email protected]]

Is there any mainstream (non-expensive) digital panel meter that can
live with less than 5V?

Don't laugh too loud, but... Why not stick a AA, C, or D cell in series
with the meter power supply? OK, this is a bad idea if you then have to
regulate the meter supply with a linear regulator, or if this makes the
meter supply too high when the system battery is fully charged. Also, if
there is a general spec of "no batteries or parts that have to be replaced"
then you lose. If it's an LCD meter, though, it probably draws very
little current and a battery may last a long time.

Matt Roberds