1.3 volt Mercury Cell Replacement

[Martin McCormick]

I have a DC multimeter that was manufactured around 1972 or so
that was intended for use by electronic technicians who happen to
be blind so there is a FET-based chopper and Wheatstone bridge in
what normally would be the meter movement. To get a reading, one
turns a wire-wound pot and listens to a steady tone on a loud
speaker. When one reaches the correct reading, the bridge
balances and the tone fades out in to a null. If you go past the
null, the tone fades back up.

The meter probably still works but one of the batteries
it uses is a 1.3 volt mercury cell which is the size of a
Double-A battery.

It got to where the 1.3-volt double-A sized cell was hard
to find so I found a N-sized cell. These are the same diameter
as a double-A but only about half as long. I made a dummy cell
out of hard copper tubing of the right diameter and stuck a
spring in the tubing to press against a piece of copper at each
end to take up the rest of the space and that worked. One simply
replaced the N cell more often.

The mercury cell is a voltage reference so the readings
are all wrong if one puts in a double-A so my question is whether
there are any more environmentally friendly 1.3-volt cells that
can replace the mercury cell.

The holder is double-A sized but I think there may be
room in the case to install a different holder such as a coin
cell if the new reference cell is shaped differently.

The other batteries are a normal D cell and a 9-volt
snap terminal battery and neither of those are special so I
should be able to revive it if I can get a 1.3-volt reference which
would replace the mercury cell. The load is rather low as I
remember that it normally lasted quite a long time before needing
to be replaced.

I keep intending to get it working again as it is a
pretty decent analog DC volt, ohm and amp meter and will read up
to ten amps on it's highest current range.

It's been sitting on my work bench for several years,
mocking me to put it back in service again.

Thanks for any constructive suggestions.

Martin McCormick WB5AGZ

[Martin McCormick]

First, I just sent this and forgot the tag. I am sorry.

I have a DC multimeter that was manufactured around 1972 or so
that was intended for use by electronic technicians who happen to
be blind so there is a FET-based chopper and Wheatstone bridge in
what normally would be the meter movement. To get a reading, one
turns a wire-wound pot and listens to a steady tone on a loud
speaker. When one reaches the correct reading, the bridge
balances and the tone fades out in to a null. If you go past the
null, the tone fades back up.

The meter probably still works but one of the batteries
it uses is a 1.3 volt mercury cell which is the size of a
Double-A battery.

It got to where the 1.3-volt double-A sized cell was hard
to find so I found a N-sized cell. These are the same diameter
as a double-A but only about half as long. I made a dummy cell
out of hard copper tubing of the right diameter and stuck a
spring in the tubing to press against a piece of copper at each
end to take up the rest of the space and that worked. One simply
replaced the N cell more often.

The mercury cell is a voltage reference so the readings
are all wrong if one puts in a double-A so my question is whether
there are any more environmentally friendly 1.3-volt cells that
can replace the mercury cell.

The holder is double-A sized but I think there may be
room in the case to install a different holder such as a coin
cell if the new reference cell is shaped differently.

The other batteries are a normal D cell and a 9-volt
snap terminal battery and neither of those are special so I
should be able to revive it if I can get a 1.3-volt reference which
would replace the mercury cell. The load is rather low as I
remember that it normally lasted quite a long time before needing
to be replaced.

I keep intending to get it working again as it is a
pretty decent analog DC volt, ohm and amp meter and will read up
to ten amps on it's highest current range.

It's been sitting on my work bench for several years,
mocking me to put it back in service again.

Thanks for any constructive suggestions.

Martin McCormick WB5AGZ

[Denny Esterline]

Depending on how much you're willing to modify the device, I'd consider
adding a new (higher voltage) cell and a voltage regulator.
Shouldn't be too hard to find a suitable low quiescent current regulator to
supply the reference voltage.

Post by Martin McCormick
First, I just sent this and forgot the tag. I am sorry.
I have a DC multimeter that was manufactured around 1972 or so
that was intended for use by electronic technicians who happen to
be blind so there is a FET-based chopper and Wheatstone bridge in
what normally would be the meter movement. To get a reading, one
turns a wire-wound pot and listens to a steady tone on a loud
speaker. When one reaches the correct reading, the bridge
balances and the tone fades out in to a null. If you go past the
null, the tone fades back up.
The meter probably still works but one of the batteries
it uses is a 1.3 volt mercury cell which is the size of a
Double-A battery.
It got to where the 1.3-volt double-A sized cell was hard
to find so I found a N-sized cell. These are the same diameter
as a double-A but only about half as long. I made a dummy cell
out of hard copper tubing of the right diameter and stuck a
spring in the tubing to press against a piece of copper at each
end to take up the rest of the space and that worked. One simply
replaced the N cell more often.
The mercury cell is a voltage reference so the readings
are all wrong if one puts in a double-A so my question is whether
there are any more environmentally friendly 1.3-volt cells that
can replace the mercury cell.
The holder is double-A sized but I think there may be
room in the case to install a different holder such as a coin
cell if the new reference cell is shaped differently.
The other batteries are a normal D cell and a 9-volt
snap terminal battery and neither of those are special so I
should be able to revive it if I can get a 1.3-volt reference which
would replace the mercury cell. The load is rather low as I
remember that it normally lasted quite a long time before needing
to be replaced.
I keep intending to get it working again as it is a
pretty decent analog DC volt, ohm and amp meter and will read up
to ten amps on it's highest current range.
It's been sitting on my work bench for several years,
mocking me to put it back in service again.
Thanks for any constructive suggestions.
Martin McCormick WB5AGZ
--
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http://mailman.mit.edu/mailman/listinfo/piclist

[Martin McCormick]

Post by Denny Esterline
Depending on how much you're willing to modify the device, I'd consider
adding a new (higher voltage) cell and a voltage regulator.
Shouldn't be too hard to find a suitable low quiescent current regulator to
supply the reference voltage.

That is an excellent suggestion and has gotten me to
thinking with one possibility being to
rob a few more mills from the 9-volt battery that runs the
chopper. There is one switch that turns power on and off to the
whole meter and I want the new battery and regulator off when the
rest of the meter is off to avoid draining the reference battery.

A small DC-DC converter that is transformer isolated and
capable of a couple of milliamps at most might also do the job.
The one rule is that there should be no path back to any of the
other batteries or they wouldn't have designed the circuit the
way they did. 1.3 volts has to magically appear where once a
battery sat.

Again, many thanks.

Martin McCormick

[Denny Esterline]

Given that this was the unit's reference voltage, I think I'd steer away
from any sources of noise - if practical or possible. Any kind of switching
regulator would certainly qualify on that front.
Russel should be along shortly to share a circuit with a TL431 :-)

I jest, that's actually not a bad solution.

-Denny

Post by Martin McCormick

Post by Denny Esterline
Depending on how much you're willing to modify the device, I'd consider
adding a new (higher voltage) cell and a voltage regulator.
Shouldn't be too hard to find a suitable low quiescent current regulator to
supply the reference voltage.

That is an excellent suggestion and has gotten me to
thinking with one possibility being to
rob a few more mills from the 9-volt battery that runs the
chopper. There is one switch that turns power on and off to the
whole meter and I want the new battery and regulator off when the
rest of the meter is off to avoid draining the reference battery.
A small DC-DC converter that is transformer isolated and
capable of a couple of milliamps at most might also do the job.
The one rule is that there should be no path back to any of the
other batteries or they wouldn't have designed the circuit the
way they did. 1.3 volts has to magically appear where once a
battery sat.
Again, many thanks.
Martin McCormick
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[RussellMc]

Post by Denny Esterline
Given that this was the unit's reference voltage, I think I'd steer away
from any sources of noise - if practical or possible. Any kind of switching
regulator would certainly qualify on that front.
Russel should be along shortly to share a circuit with a TL431 :-)
Zetex version of TL431 due to usefully lower Iq than most.

But most TLV431 (half Vreg_std of TL431) have usefuilly lower Iq.

Post by Denny Esterline
From memory TL431 is about 80 uA max and T:V431 about 25 uS max. Memory may

be wrong.

BUT LM385 can be far lower AFAIR (a few uA)

http://www.ti.com/lit/ds/symlink/lm185-1.2-n.pdf

Annoyingly the 10 uA Iq ones are foxed.
And the adjustables are about 50 uA Iq.

but

Some of these 3 terminal regulators look "just right"


https://www.digikey.com/products/en/integrated-circuits-ics/pmic-voltage-regulators-linear/699?FV=ffe002bb%2C1bcc0120%2C1bcc0121%2C1bcc001d%2C1bcc0125%2C1bcc0126%2C1bcc0197%2C1bcc0262%2C1bcc0325%2C1bcc0326%2C1bcc0366%2C1bcc039d%2C1bcc039e&quantity=0&ColumnSort=477&page=1&k=ldo&pageSize=25&pkeyword=ldo

Including this:

eg $0.97/1 in stock Digikey - 1.3V version

*https://www.ablic.com/en/doc/datasheet/voltage_regulator/S1313_E.pdf
<https://www.ablic.com/en/doc/datasheet/voltage_regulator/S1313_E.pdf>*

SOT23-5

Output voltage: 1.0 V to 3.5 V, selectable in 0.05 V step.
Input voltage: 1.5 V to 5.5 V
Output voltage accuracy:
1.0% (1.0 V to 1.45 V
Dropout voltage: 170 mV typ.
IOUT = 100 mA

*Current consumption*:
During operation: 0.9uA typ., 1.35 uA max.
During power-off: 0.01 uA typ., 0.1 uA max.

The need to "float" the battery may be able to be overcome by feeding it
from 9V with two resistors to +9V and ground.

R < (V9Vmin-Vout-Vdropout)/Imax/2


Russell

[m***@tutanota.com]

As 9V batteries don't store much energy I'd suggest running the 1.3V portion with a switcher running off the D-cell as these are the largest energy source in the meter you describe.  If you use an alkaline or Nimh battery for the D-cell  you can use a step up. 

You could build the switcher into a  "fake" cell that fits in the mercury battery holder and just have a couple of very small wires from it to the D-cell.  As I mentioned there are switchers that draw less current when not under load Than what the battery leaks internally.  Presumably the meter disconnects the reference cell completely when the meter is off, though you may want to check.  If you are going to use a rechargeable D-cell you could also provide the +9V source as well, reducing 3 batteries to 1 battery that is rechargeable.  The charge circuit would fit in the 9V cell place with a jack for  a wall wart so the battery never has to be taken out.

"We the People Dare to Create a More Perfect Union" <aclu.org>

Post by Martin McCormick
First, I just sent this and forgot the tag. I am sorry.
I have a DC multimeter that was manufactured around 1972 or so
that was intended for use by electronic technicians who happen to
be blind so there is a FET-based chopper and Wheatstone bridge in
what normally would be the meter movement. To get a reading, one
turns a wire-wound pot and listens to a steady tone on a loud
speaker. When one reaches the correct reading, the bridge
balances and the tone fades out in to a null. If you go past the
null, the tone fades back up.
The meter probably still works but one of the batteries
it uses is a 1.3 volt mercury cell which is the size of a
Double-A battery.
It got to where the 1.3-volt double-A sized cell was hard
to find so I found a N-sized cell. These are the same diameter
as a double-A but only about half as long. I made a dummy cell
out of hard copper tubing of the right diameter and stuck a
spring in the tubing to press against a piece of copper at each
end to take up the rest of the space and that worked. One simply
replaced the N cell more often.
The mercury cell is a voltage reference so the readings
are all wrong if one puts in a double-A so my question is whether
there are any more environmentally friendly 1.3-volt cells that
can replace the mercury cell.
The holder is double-A sized but I think there may be
room in the case to install a different holder such as a coin
cell if the new reference cell is shaped differently.
The other batteries are a normal D cell and a 9-volt
snap terminal battery and neither of those are special so I
should be able to revive it if I can get a 1.3-volt reference which
would replace the mercury cell. The load is rather low as I
remember that it normally lasted quite a long time before needing
to be replaced.
I keep intending to get it working again as it is a
pretty decent analog DC volt, ohm and amp meter and will read up
to ten amps on it's highest current range.
It's been sitting on my work bench for several years,
mocking me to put it back in service again.
Thanks for any constructive suggestions.
Martin McCormick WB5AGZ
--
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[Spehro Pefhany]

I extended the life of a similar thermocouple measurement box by adding alkaline batteries and a voltage regulator. I used an LM317 because it was decades ago, but you can use a better regulator or reference.

The box I modified used a standard (Weston) cell and was recalibrated before each measurement-in your case you probably want something a bit more stable.

Best regards, Spehro Pefhany

Post by Martin McCormick
I have a DC multimeter that was manufactured around 1972 or so
that was intended for use by electronic technicians who happen to
be blind so there is a FET-based chopper and Wheatstone bridge in
what normally would be the meter movement. To get a reading, one
turns a wire-wound pot and listens to a steady tone on a loud
speaker. When one reaches the correct reading, the bridge
balances and the tone fades out in to a null. If you go past the
null, the tone fades back up.
The meter probably still works but one of the batteries
it uses is a 1.3 volt mercury cell which is the size of a
Double-A battery.
It got to where the 1.3-volt double-A sized cell was hard
to find so I found a N-sized cell. These are the same diameter
as a double-A but only about half as long. I made a dummy cell
out of hard copper tubing of the right diameter and stuck a
spring in the tubing to press against a piece of copper at each
end to take up the rest of the space and that worked. One simply
replaced the N cell more often.
The mercury cell is a voltage reference so the readings
are all wrong if one puts in a double-A so my question is whether
there are any more environmentally friendly 1.3-volt cells that
can replace the mercury cell.
The holder is double-A sized but I think there may be
room in the case to install a different holder such as a coin
cell if the new reference cell is shaped differently.
The other batteries are a normal D cell and a 9-volt
snap terminal battery and neither of those are special so I
should be able to revive it if I can get a 1.3-volt reference which
would replace the mercury cell. The load is rather low as I
remember that it normally lasted quite a long time before needing
to be replaced.
I keep intending to get it working again as it is a
pretty decent analog DC volt, ohm and amp meter and will read up
to ten amps on it's highest current range.
It's been sitting on my work bench for several years,
mocking me to put it back in service again.
Thanks for any constructive suggestions.
Martin McCormick WB5AGZ
--
http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive
View/change your membership options at
http://mailman.mit.edu/mailman/listinfo/piclist

[Martin McCormick]

Post by Spehro Pefhany
I extended the life of a similar thermocouple measurement box by adding
alkaline batteries and a voltage regulator. I used an LM317 because it
was decades ago, but you can use a better regulator or reference.
The box I modified used a standard (Weston) cell and was recalibrated
before each measurement-in your case you probably want something a bit
more stable.
Best regards, Spehro Pefhany

Thank you. I am sure I will end up doing something
similar with the only complication being a way to turn off power
to the new regulator when power should be off to the whole meter.

I am thinking maybe an optoisolator with the LED drive
coming from the 9-volt battery that drives the chopper. When it
is on, the meter is in use and it's okay to generate the 1.3
volts. If the meter is off, then that regulator circuit also
needs to be off so as not to drain it's battery.

Martin

[m***@tutanota.com]

I'd suggest using a switching power supply with cycle skipping for long life.  I.E. when the meter isn't drawing power the switcher will use less current than the leakage current in the battery (depending on type of cell).  There are also now low current power supplies available that put the whole circuit inside the inductor windings designed for just this application.   I can't find the supplies neatly tucked into the inductor but these are nearly as small and really don't need to be turned off in most applications.  <https://www.maximintegrated.com/en/products/power/nanopower-dc-dc-regulators.html>. <https://www.maximintegrated.com/en/products/power/nanopower-dc-dc-regulators.html>  There are other companies of course but maxim has been one of the better companies for battery applications.

"We the People Dare to Create a More Perfect Union" <aclu.org>

Post by Martin McCormick

Post by Spehro Pefhany
I extended the life of a similar thermocouple measurement box by adding
alkaline batteries and a voltage regulator. I used an LM317 because it
was decades ago, but you can use a better regulator or reference.
The box I modified used a standard (Weston) cell and was recalibrated
before each measurement-in your case you probably want something a bit
more stable.
Best regards, Spehro Pefhany

Thank you. I am sure I will end up doing something
similar with the only complication being a way to turn off power
to the new regulator when power should be off to the whole meter.
I am thinking maybe an optoisolator with the LED drive
coming from the 9-volt battery that drives the chopper. When it
is on, the meter is in use and it's okay to generate the 1.3
volts. If the meter is off, then that regulator circuit also
needs to be off so as not to drain it's battery.
Martin
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[Denny Esterline]

That sparked a braincell or two..
Take a look at a TLP190B (there is a few other family members as well)
It's a photovoltaic optioisolator. Think LED and solar cell in the same
package.
Often used to drive the gate on FETs, but can produce several volts at 10+
uA
Not sure how mach you need to replace the mercury battery, but this may be
an option with a bit of creativity.

Post by Martin McCormick

Post by Spehro Pefhany
I extended the life of a similar thermocouple measurement box by adding
alkaline batteries and a voltage regulator. I used an LM317 because it
was decades ago, but you can use a better regulator or reference.
The box I modified used a standard (Weston) cell and was recalibrated
before each measurement-in your case you probably want something a bit
more stable.
Best regards, Spehro Pefhany

Thank you. I am sure I will end up doing something
similar with the only complication being a way to turn off power
to the new regulator when power should be off to the whole meter.
I am thinking maybe an optoisolator with the LED drive
coming from the 9-volt battery that drives the chopper. When it
is on, the meter is in use and it's okay to generate the 1.3
volts. If the meter is off, then that regulator circuit also
needs to be off so as not to drain it's battery.
Martin
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[Martin McCormick]

Post by Denny Esterline
That sparked a braincell or two..
Take a look at a TLP190B (there is a few other family members as well)
It's a photovoltaic optioisolator. Think LED and solar cell in the same
package.
Often used to drive the gate on FETs, but can produce several volts at 10+
uA
Not sure how mach you need to replace the mercury battery, but this may be
an option with a bit of creativity.

Wow! I was sitting here wishing that something like that
existed. The question will be how many uA the circuit draws
under use.

I can probably find that out by taking a second
multimeter and read the current draw through a double-A battery.
A 1.3-volt source will see a draw slightly lower but I will probably
be able to tell whether something like this might work.

The only other thing I am not totally sure of is whether
or not these parts are made in through-hole style as the data
sheet I read only mentioned surface mount packages.

It sounds like a very interesting device if I can get a
through-hole version.

Thanks for the info.

Martin McCormick

[Denny Esterline]

I've not see it as a through hole version, but it's probably one of the
easiest surface mount parts to solder.
Since it's an isolator, the pin spacing is quite generous.

Post by Martin McCormick

Post by Denny Esterline
That sparked a braincell or two..
Take a look at a TLP190B (there is a few other family members as well)
It's a photovoltaic optioisolator. Think LED and solar cell in the same
package.
Often used to drive the gate on FETs, but can produce several volts at

10+

Post by Denny Esterline
uA
Not sure how mach you need to replace the mercury battery, but this may

be

Post by Denny Esterline
an option with a bit of creativity.

Wow! I was sitting here wishing that something like that
existed. The question will be how many uA the circuit draws
under use.
I can probably find that out by taking a second
multimeter and read the current draw through a double-A battery.
A 1.3-volt source will see a draw slightly lower but I will probably
be able to tell whether something like this might work.
The only other thing I am not totally sure of is whether
or not these parts are made in through-hole style as the data
sheet I read only mentioned surface mount packages.
It sounds like a very interesting device if I can get a
through-hole version.
Thanks for the info.
Martin McCormick
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[Martin McCormick]

It is good to know these parts exist but I am not as excited as I
was. As one who is blind, I have been able to prototype easily
over the past 35 or so years with through-hole and wire-wrap
technology and I certainly understand why everything is going
surface-mount since it is easy to crank out a million widgets
with parts on both sides of a board and the performance is better
as the surface-mount parts do not have as much stray capacitance
and inductance as do through-hole parts but to do one's and two's this
way is a lot more trouble and expense and, if you discover that
the board needs a modification, you either go through the whole
process again or tack something together with wire-wrap wire and
hope it doesn't touch something else after a bit of vibration.

I have used wire-wrap sockets that hold surface-mount
parts such as the Motorola 68HC11. That chip has 52 pins at .05
inch spacing and it snaps in to a socket which has 52
through-hole pins that can even be pushed in to a corresponding
wire-wrap socket.

The footprint on the other side is a square within a
slightly larger square with all the pins being on .1-inch
centers so it fits in to perph board. You count even numbers
around one square and odd numbers in the other square.

When I solder, it is to the round leads of components and
to ground and VCC strips as the round leads eventually unwrap
themselves especially if they are allowed to wiggle so the idea
is to make the leads fast. Wire wrap pins are square and the
wire bites in to each pin and tends to stay good forever.

The TLP190B chip sounds like it is a gull-wing form
which means a socket probably could be made if it firmly held the
rows of pins in a little vice.

I am not arguing that through-hole construction is
superior, only that prototyping technology should exist that
works for very limited runs.

When you can design and build a solution on a little
square of perforated board and stick it in something for 30
years, that's useful.

In case anybody is curious, .1-inch spacing is still
fairly easy to navigate. .05-inch spacing is harder for normal
fingers to resolve. It gets to the point where one's fingers
can't feel enough resolution to tell whether or not one is doing
well or making a mess of things.

A toothpick or the end of a pin is sometimes helpful in
counting a long line of pins and one's fingernails can usually
feel if solder is smooth or crusty. Crusty usually means trouble.

Note to the slow. Let it cool down first.

Martin

[RussellMc]

It is good to know these parts exist but I am not as excited as I

Post by Martin McCormick
was. As one who is blind, I have been able to prototype easily
over the past 35 or so years with through-hole and wire-wrap
technology and I certainly understand why everything is going
surface-mount since it is easy to crank out a million widgets
with parts on both sides of a board and the performance is better
as the surface-mount parts do not have as much stray capacitance
and inductance as do through-hole parts but to do one's and two's this
way is a lot more trouble and expense and, if you discover that
the board needs a modification, you either go through the whole
process again or tack something together with wire-wrap wire and
hope it doesn't touch something else after a bit of vibration.

Agh!

OK - DIP 8, 4 uA quiescent, dual regulators,
Vout 1.4V to 16V variable.

In stock Digikey $2.70/1
https://www.digikey.com/product-detail/en/renesas-electronics-america-inc/ICL7663SCPAZ/ICL7663SCPAZ-ND/1063222

• Guaranteed 10A Maximum Quiescent Current Over All
Temperature Ranges
• Wider Operating Voltage Range - 1.6V to 16V
• Guaranteed Line and Load Regulation Over Entire
Operating Temperature Range Optional
• 1% Output Voltage Accuracy (ICL7663SA)
• Output Voltage Programmable from 1.3V to 16V
• Improved Temperature Coefficient of Output Voltage
• 40mA Minimum Output Current with Current Limiting
• Output Voltages with Programmable Negative
Temperature Coefficients
• Output Shutdown via Current-Limit Sensing or External
Logic Level
• Low Input-to-Output Voltage Differential
• Improved Direct Replacement for Industry Standard
ICL7663B and Other Second-Source Products


Datasheet
https://www.intersil.com/content/dam/Intersil/documents/icl7/icl7663s.pdf


Russell

[Sean Breheny]

Hi Martin,

I was taught how to build and repair PCs by a blind man in the 1990s. He
was very resourceful as it is clear that you are, too. I have used these
photovoltaic optos before and the pitch is even wider than 0.1 inch so I am
sure you could manage it. The problem is that I believe they only output
around 10uA but you'd have to check the datasheet for the particular one
you have in mind.

Sean

Post by Martin McCormick
It is good to know these parts exist but I am not as excited as I
was. As one who is blind, I have been able to prototype easily
over the past 35 or so years with through-hole and wire-wrap
technology and I certainly understand why everything is going
surface-mount since it is easy to crank out a million widgets
with parts on both sides of a board and the performance is better
as the surface-mount parts do not have as much stray capacitance
and inductance as do through-hole parts but to do one's and two's this
way is a lot more trouble and expense and, if you discover that
the board needs a modification, you either go through the whole
process again or tack something together with wire-wrap wire and
hope it doesn't touch something else after a bit of vibration.
I have used wire-wrap sockets that hold surface-mount
parts such as the Motorola 68HC11. That chip has 52 pins at .05
inch spacing and it snaps in to a socket which has 52
through-hole pins that can even be pushed in to a corresponding
wire-wrap socket.
The footprint on the other side is a square within a
slightly larger square with all the pins being on .1-inch
centers so it fits in to perph board. You count even numbers
around one square and odd numbers in the other square.
When I solder, it is to the round leads of components and
to ground and VCC strips as the round leads eventually unwrap
themselves especially if they are allowed to wiggle so the idea
is to make the leads fast. Wire wrap pins are square and the
wire bites in to each pin and tends to stay good forever.
The TLP190B chip sounds like it is a gull-wing form
which means a socket probably could be made if it firmly held the
rows of pins in a little vice.
I am not arguing that through-hole construction is
superior, only that prototyping technology should exist that
works for very limited runs.
When you can design and build a solution on a little
square of perforated board and stick it in something for 30
years, that's useful.
In case anybody is curious, .1-inch spacing is still
fairly easy to navigate. .05-inch spacing is harder for normal
fingers to resolve. It gets to the point where one's fingers
can't feel enough resolution to tell whether or not one is doing
well or making a mess of things.
A toothpick or the end of a pin is sometimes helpful in
counting a long line of pins and one's fingernails can usually
feel if solder is smooth or crusty. Crusty usually means trouble.
Note to the slow. Let it cool down first.
Martin
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[Martin McCormick]

Post by Sean Breheny
Hi Martin,
I was taught how to build and repair PCs by a blind man in the 1990s. He
was very resourceful as it is clear that you are, too. I have used these
photovoltaic optos before and the pitch is even wider than 0.1 inch so I am
sure you could manage it. The problem is that I believe they only output
around 10uA but you'd have to check the datasheet for the particular one
you have in mind.

Thank you. I should be able to determine the actual current
requirement by running the meter in the mode that uses the cell
and using a second multimeter to see what the draw is on that
cell.

More than likely, it will be more than 10uA but it sure
is worth a try.

If it is, then it will be another battery and a regulator
plus a sense circuit to detect when the meter is needing that
power source.

I will probably buy a couple of TLP190B's the next time I
buy parts even if they don't work in this circuit. They might
work as phantom voltage sources for condenser microphones or
anywhere one needs very low current that shouldn't reference the
system's power supply for whatever reason.

Martin WB5AGZ

[Denny Esterline]

If it's close-ish, you could parallel a couple of them for more current
It's been a couple years, but somewhere in the foggy mist of my mind I seem
to recall somebody stuffing hundreds of them on a PCB for that very reason.