juggling parts...

[server]

Once you have a few resistors on a schematic, it\'s tempting to do what
you want using existing values. That reduces the BOM and the
pick-and-place setup. There are far more possibilities if you are
willing to compromise things some, or put resistors in series and
parallel. This is a 4-page schematic with 9 different resistors. Doing
this is an enormous PITA.

https://www.dropbox.com/s/aozh6m6mmmik6lb/T502_Parts.jpg?raw=1

Saved a DAC reference chip! Actually, having the DAC voltage
ratiometric on +15 is a benefit here.

That opamp should be stable with the tantalum load and a 1u ceramic at
the DAC, but I\'ll verify that.




--

Father Brown\'s figure remained quite dark and still;
but in that instant he had lost his head. His head was
always most valuable when he had lost it.

 

[Jan Panteltje]

On a sunny day (Sun, 14 Nov 2021 10:27:20 -0800) it happened
jlarkin@highlandsniptechnology.com wrote in
<slk2pghav4cqdg31k20lnr0i2m63k5t6ur@4ax.com>:

On Sun, 14 Nov 2021 17:59:06 GMT, Jan Panteltje
pNaOnStPeAlMtje@yahoo.com> wrote:

On a sunny day (Sun, 14 Nov 2021 09:39:03 -0800) it happened
jlarkin@highlandsniptechnology.com wrote in
1ch2pgh4echute3tflmia84j7uosmor4rv@4ax.com>:

On Sun, 14 Nov 2021 17:11:29 GMT, Jan Panteltje
pNaOnStPeAlMtje@yahoo.com> wrote:

On a sunny day (Sun, 14 Nov 2021 08:39:13 -0800) it happened
jlarkin@highlandsniptechnology.com wrote in
54e2pgl0ir9ucjhtrcq35c0dj7pkadrgf8@4ax.com>:


Once you have a few resistors on a schematic, it\'s tempting to do what
you want using existing values. That reduces the BOM and the
pick-and-place setup. There are far more possibilities if you are
willing to compromise things some, or put resistors in series and
parallel. This is a 4-page schematic with 9 different resistors. Doing
this is an enormous PITA.

https://www.dropbox.com/s/aozh6m6mmmik6lb/T502_Parts.jpg?raw=1

Saved a DAC reference chip! Actually, having the DAC voltage
ratiometric on +15 is a benefit here.

That opamp should be stable with the tantalum load and a 1u ceramic at
the DAC, but I\'ll verify that.

Or a second LM317 for the +3V?

Yuk! That would involve an entire new chain of value juggling.

Really?


The resistor ratio needs to be 1.4:1. I can get 3.125 volts with three
resistors.

What I do not get is: you sell expensive things in low quantity and try to save on a trimpot?

Trimpots are expensive and need manual turning. DACs are automated and
can have cal factors stored in cal tables. I\'m using 16-bit DACs and
there are no 16-bit trimpots.

Some of my customers absolutely forbid trimpots, which I think is
extreme. Once in a while they make sense. They say that if there\'s a
pot, their techs will turn it.


or waste board space with funny resistor combinations?

I have space on this one for a few more 0603s. It\'s inefficient to
load a reel onto the pick-and-place just for one resistor.

The LM317 is huge.

I mean I use 3 resistors to get a LM317 to output some specific voltage all the time..
mostly different ones.
Sure you can use 1 Ohm resistors to do most things, but then you need many,,,,
10 Ohm would work too here.


The +15 charges a timing ramp through resistors, and the DAC feeds
some timing comparators, so it\'s nice if they are ratiometric. 317\'s
are not very good references.

Data sheets suggest that an LM317 can\'t make 3 volts from 5 volts, so
I\'d have to power it off +24.

Power it from the 15V you made with the first one.


OK, but the little opamp works better. Same number of parts, much
smaller, more stable, uses available values. That\'s the game here.

All true
As far as trimmers go, I remember the story of that guy who brought in a defective
radio and said: \"All those screws in those metal cans were loose, I fastened all of those.\"

I have trimpots in use in many things, some have been on for decades.

 

[server]

On Sun, 14 Nov 2021 19:59:43 GMT, Jan Panteltje
<pNaOnStPeAlMtje@yahoo.com> wrote:

On a sunny day (Sun, 14 Nov 2021 10:27:20 -0800) it happened
jlarkin@highlandsniptechnology.com wrote in
slk2pghav4cqdg31k20lnr0i2m63k5t6ur@4ax.com>:

On Sun, 14 Nov 2021 17:59:06 GMT, Jan Panteltje
pNaOnStPeAlMtje@yahoo.com> wrote:

On a sunny day (Sun, 14 Nov 2021 09:39:03 -0800) it happened
jlarkin@highlandsniptechnology.com wrote in
1ch2pgh4echute3tflmia84j7uosmor4rv@4ax.com>:

On Sun, 14 Nov 2021 17:11:29 GMT, Jan Panteltje
pNaOnStPeAlMtje@yahoo.com> wrote:

On a sunny day (Sun, 14 Nov 2021 08:39:13 -0800) it happened
jlarkin@highlandsniptechnology.com wrote in
54e2pgl0ir9ucjhtrcq35c0dj7pkadrgf8@4ax.com>:


Once you have a few resistors on a schematic, it\'s tempting to do what
you want using existing values. That reduces the BOM and the
pick-and-place setup. There are far more possibilities if you are
willing to compromise things some, or put resistors in series and
parallel. This is a 4-page schematic with 9 different resistors. Doing
this is an enormous PITA.

https://www.dropbox.com/s/aozh6m6mmmik6lb/T502_Parts.jpg?raw=1

Saved a DAC reference chip! Actually, having the DAC voltage
ratiometric on +15 is a benefit here.

That opamp should be stable with the tantalum load and a 1u ceramic at
the DAC, but I\'ll verify that.

Or a second LM317 for the +3V?

Yuk! That would involve an entire new chain of value juggling.

Really?


The resistor ratio needs to be 1.4:1. I can get 3.125 volts with three
resistors.

What I do not get is: you sell expensive things in low quantity and try to save on a trimpot?

Trimpots are expensive and need manual turning. DACs are automated and
can have cal factors stored in cal tables. I\'m using 16-bit DACs and
there are no 16-bit trimpots.

Some of my customers absolutely forbid trimpots, which I think is
extreme. Once in a while they make sense. They say that if there\'s a
pot, their techs will turn it.


or waste board space with funny resistor combinations?

I have space on this one for a few more 0603s. It\'s inefficient to
load a reel onto the pick-and-place just for one resistor.

The LM317 is huge.

I mean I use 3 resistors to get a LM317 to output some specific voltage all the time..
mostly different ones.
Sure you can use 1 Ohm resistors to do most things, but then you need many,,,,
10 Ohm would work too here.


The +15 charges a timing ramp through resistors, and the DAC feeds
some timing comparators, so it\'s nice if they are ratiometric. 317\'s
are not very good references.

Data sheets suggest that an LM317 can\'t make 3 volts from 5 volts, so
I\'d have to power it off +24.

Power it from the 15V you made with the first one.


OK, but the little opamp works better. Same number of parts, much
smaller, more stable, uses available values. That\'s the game here.

All true
As far as trimmers go, I remember the story of that guy who brought in a defective
radio and said: \"All those screws in those metal cans were loose, I fastened all of those.\"

I have trimpots in use in many things, some have been on for decades.

One good use for small trimpots is to set the gain in wideband -
hundreds of MHz - things like photodiode amps. Especially when the
product is not digital.

Analog multipliers are expensive and relatively slow. PIN diodes are
great but don\'t work at low frequencies or DC. A tiny DIP switch and
resistors are OK if you don\'t mind coarse resolution. There are some
super wideband many-bits digital RF attenuators, for around $100 each.

Selected resistors are a nuisance.

I think the wonderful Murata 2mm pots are extinct. They worked at 1
GHz or so. And were horrible to adjust.





--

Father Brown\'s figure remained quite dark and still;
but in that instant he had lost his head. His head was
always most valuable when he had lost it.

 

[server]

On Sun, 14 Nov 2021 19:59:43 GMT, Jan Panteltje
<pNaOnStPeAlMtje@yahoo.com> wrote:

On a sunny day (Sun, 14 Nov 2021 10:27:20 -0800) it happened
jlarkin@highlandsniptechnology.com wrote in
slk2pghav4cqdg31k20lnr0i2m63k5t6ur@4ax.com>:

On Sun, 14 Nov 2021 17:59:06 GMT, Jan Panteltje
pNaOnStPeAlMtje@yahoo.com> wrote:

On a sunny day (Sun, 14 Nov 2021 09:39:03 -0800) it happened
jlarkin@highlandsniptechnology.com wrote in
1ch2pgh4echute3tflmia84j7uosmor4rv@4ax.com>:

On Sun, 14 Nov 2021 17:11:29 GMT, Jan Panteltje
pNaOnStPeAlMtje@yahoo.com> wrote:

On a sunny day (Sun, 14 Nov 2021 08:39:13 -0800) it happened
jlarkin@highlandsniptechnology.com wrote in
54e2pgl0ir9ucjhtrcq35c0dj7pkadrgf8@4ax.com>:


Once you have a few resistors on a schematic, it\'s tempting to do what
you want using existing values. That reduces the BOM and the
pick-and-place setup. There are far more possibilities if you are
willing to compromise things some, or put resistors in series and
parallel. This is a 4-page schematic with 9 different resistors. Doing
this is an enormous PITA.

https://www.dropbox.com/s/aozh6m6mmmik6lb/T502_Parts.jpg?raw=1

Saved a DAC reference chip! Actually, having the DAC voltage
ratiometric on +15 is a benefit here.

That opamp should be stable with the tantalum load and a 1u ceramic at
the DAC, but I\'ll verify that.

Or a second LM317 for the +3V?

Yuk! That would involve an entire new chain of value juggling.

Really?


The resistor ratio needs to be 1.4:1. I can get 3.125 volts with three
resistors.

What I do not get is: you sell expensive things in low quantity and try to save on a trimpot?

Trimpots are expensive and need manual turning. DACs are automated and
can have cal factors stored in cal tables. I\'m using 16-bit DACs and
there are no 16-bit trimpots.

Some of my customers absolutely forbid trimpots, which I think is
extreme. Once in a while they make sense. They say that if there\'s a
pot, their techs will turn it.


or waste board space with funny resistor combinations?

I have space on this one for a few more 0603s. It\'s inefficient to
load a reel onto the pick-and-place just for one resistor.

The LM317 is huge.

I mean I use 3 resistors to get a LM317 to output some specific voltage all the time..
mostly different ones.
Sure you can use 1 Ohm resistors to do most things, but then you need many,,,,
10 Ohm would work too here.


The +15 charges a timing ramp through resistors, and the DAC feeds
some timing comparators, so it\'s nice if they are ratiometric. 317\'s
are not very good references.

Data sheets suggest that an LM317 can\'t make 3 volts from 5 volts, so
I\'d have to power it off +24.

Power it from the 15V you made with the first one.


OK, but the little opamp works better. Same number of parts, much
smaller, more stable, uses available values. That\'s the game here.

All true
As far as trimmers go, I remember the story of that guy who brought in a defective
radio and said: \"All those screws in those metal cans were loose, I fastened all of those.\"

I have trimpots in use in many things, some have been on for decades.

One good use for small trimpots is to set the gain in wideband -
hundreds of MHz - things like photodiode amps. Especially when the
product is not digital.

Analog multipliers are expensive and relatively slow. PIN diodes are
great but don\'t work at low frequencies or DC. A tiny DIP switch and
resistors are OK if you don\'t mind coarse resolution. There are some
super wideband many-bits digital RF attenuators, for around $100 each.

Selected resistors are a nuisance.

I think the wonderful Murata 2mm pots are extinct. They worked at 1
GHz or so. And were horrible to adjust.





--

Father Brown\'s figure remained quite dark and still;
but in that instant he had lost his head. His head was
always most valuable when he had lost it.

 

[Edward Hernandez]

The John Doe troll stated the following in message-id
<sdhn7c$pkp$4@dont-email.me>:

> The troll doesn\'t even know how to format a USENET post...

And the John Doe troll stated the following in message-id
<sg3kr7$qt5$1@dont-email.me>:

The reason Bozo cannot figure out how to get Google to keep from
breaking its lines in inappropriate places is because Bozo is
CLUELESS...

And yet, the clueless John Doe troll has itself posted yet another
incorrectly formatted USENET posting on Wed, 17 Nov 2021 08:18:42 -0000
(UTC) in message-id <sn2dt2$s3e$5@dont-email.me>.

This posting is a public service announcement for any google groups
readers who happen by to point out that the John Doe troll does not even
follow it\'s own rules that it uses to troll other posters.

1gPN3spxiUqo

 

[Edward Hernandez]

The John Doe troll stated the following in message-id
<sdhn7c$pkp$4@dont-email.me>:

> The troll doesn\'t even know how to format a USENET post...

And the John Doe troll stated the following in message-id
<sg3kr7$qt5$1@dont-email.me>:

The reason Bozo cannot figure out how to get Google to keep from
breaking its lines in inappropriate places is because Bozo is
CLUELESS...

And yet, the clueless John Doe troll has itself posted yet another
incorrectly formatted USENET posting on Wed, 17 Nov 2021 08:18:42 -0000
(UTC) in message-id <sn2dt2$s3e$5@dont-email.me>.

This posting is a public service announcement for any google groups
readers who happen by to point out that the John Doe troll does not even
follow it\'s own rules that it uses to troll other posters.

1gPN3spxiUqo

 

[TTman]

On 14/11/2021 18:27, jlarkin@highlandsniptechnology.com wrote:

On Sun, 14 Nov 2021 17:59:06 GMT, Jan Panteltje
pNaOnStPeAlMtje@yahoo.com> wrote:

On a sunny day (Sun, 14 Nov 2021 09:39:03 -0800) it happened
jlarkin@highlandsniptechnology.com wrote in
1ch2pgh4echute3tflmia84j7uosmor4rv@4ax.com>:

On Sun, 14 Nov 2021 17:11:29 GMT, Jan Panteltje
pNaOnStPeAlMtje@yahoo.com> wrote:

On a sunny day (Sun, 14 Nov 2021 08:39:13 -0800) it happened
jlarkin@highlandsniptechnology.com wrote in
54e2pgl0ir9ucjhtrcq35c0dj7pkadrgf8@4ax.com>:


Once you have a few resistors on a schematic, it\'s tempting to do what
you want using existing values. That reduces the BOM and the
pick-and-place setup. There are far more possibilities if you are
willing to compromise things some, or put resistors in series and
parallel. This is a 4-page schematic with 9 different resistors. Doing
this is an enormous PITA.

https://www.dropbox.com/s/aozh6m6mmmik6lb/T502_Parts.jpg?raw=1

Saved a DAC reference chip! Actually, having the DAC voltage
ratiometric on +15 is a benefit here.

That opamp should be stable with the tantalum load and a 1u ceramic at
the DAC, but I\'ll verify that.

Or a second LM317 for the +3V?

Yuk! That would involve an entire new chain of value juggling.

Really?


The resistor ratio needs to be 1.4:1. I can get 3.125 volts with three
resistors.

What I do not get is: you sell expensive things in low quantity and try to save on a trimpot?

Trimpots are expensive and need manual turning. DACs are automated and
can have cal factors stored in cal tables. I\'m using 16-bit DACs and
there are no 16-bit trimpots.

Some of my customers absolutely forbid trimpots, which I think is
extreme. Once in a while they make sense. They say that if there\'s a
pot, their techs will turn it.


or waste board space with funny resistor combinations?

I have space on this one for a few more 0603s. It\'s inefficient to
load a reel onto the pick-and-place just for one resistor.

The LM317 is huge.

I mean I use 3 resistors to get a LM317 to output some specific voltage all the time..
mostly different ones.
Sure you can use 1 Ohm resistors to do most things, but then you need many,,,,
10 Ohm would work too here.


The +15 charges a timing ramp through resistors, and the DAC feeds
some timing comparators, so it\'s nice if they are ratiometric. 317\'s
are not very good references.

Data sheets suggest that an LM317 can\'t make 3 volts from 5 volts, so
I\'d have to power it off +24.

Power it from the 15V you made with the first one.


OK, but the little opamp works better. Same number of parts, much
smaller, more stable, uses available values. That\'s the game here.





Pots are your enemy...

--
This email has been checked for viruses by Avast antivirus software.
https://www.avast.com/antivirus

 

[TTman]

On 14/11/2021 18:27, jlarkin@highlandsniptechnology.com wrote:

On Sun, 14 Nov 2021 17:59:06 GMT, Jan Panteltje
pNaOnStPeAlMtje@yahoo.com> wrote:

On a sunny day (Sun, 14 Nov 2021 09:39:03 -0800) it happened
jlarkin@highlandsniptechnology.com wrote in
1ch2pgh4echute3tflmia84j7uosmor4rv@4ax.com>:

On Sun, 14 Nov 2021 17:11:29 GMT, Jan Panteltje
pNaOnStPeAlMtje@yahoo.com> wrote:

On a sunny day (Sun, 14 Nov 2021 08:39:13 -0800) it happened
jlarkin@highlandsniptechnology.com wrote in
54e2pgl0ir9ucjhtrcq35c0dj7pkadrgf8@4ax.com>:


Once you have a few resistors on a schematic, it\'s tempting to do what
you want using existing values. That reduces the BOM and the
pick-and-place setup. There are far more possibilities if you are
willing to compromise things some, or put resistors in series and
parallel. This is a 4-page schematic with 9 different resistors. Doing
this is an enormous PITA.

https://www.dropbox.com/s/aozh6m6mmmik6lb/T502_Parts.jpg?raw=1

Saved a DAC reference chip! Actually, having the DAC voltage
ratiometric on +15 is a benefit here.

That opamp should be stable with the tantalum load and a 1u ceramic at
the DAC, but I\'ll verify that.

Or a second LM317 for the +3V?

Yuk! That would involve an entire new chain of value juggling.

Really?


The resistor ratio needs to be 1.4:1. I can get 3.125 volts with three
resistors.

What I do not get is: you sell expensive things in low quantity and try to save on a trimpot?

Trimpots are expensive and need manual turning. DACs are automated and
can have cal factors stored in cal tables. I\'m using 16-bit DACs and
there are no 16-bit trimpots.

Some of my customers absolutely forbid trimpots, which I think is
extreme. Once in a while they make sense. They say that if there\'s a
pot, their techs will turn it.


or waste board space with funny resistor combinations?

I have space on this one for a few more 0603s. It\'s inefficient to
load a reel onto the pick-and-place just for one resistor.

The LM317 is huge.

I mean I use 3 resistors to get a LM317 to output some specific voltage all the time..
mostly different ones.
Sure you can use 1 Ohm resistors to do most things, but then you need many,,,,
10 Ohm would work too here.


The +15 charges a timing ramp through resistors, and the DAC feeds
some timing comparators, so it\'s nice if they are ratiometric. 317\'s
are not very good references.

Data sheets suggest that an LM317 can\'t make 3 volts from 5 volts, so
I\'d have to power it off +24.

Power it from the 15V you made with the first one.


OK, but the little opamp works better. Same number of parts, much
smaller, more stable, uses available values. That\'s the game here.





Pots are your enemy...

--
This email has been checked for viruses by Avast antivirus software.
https://www.avast.com/antivirus

 

[TTman]

On 14/11/2021 18:27, jlarkin@highlandsniptechnology.com wrote:

On Sun, 14 Nov 2021 17:59:06 GMT, Jan Panteltje
pNaOnStPeAlMtje@yahoo.com> wrote:

On a sunny day (Sun, 14 Nov 2021 09:39:03 -0800) it happened
jlarkin@highlandsniptechnology.com wrote in
1ch2pgh4echute3tflmia84j7uosmor4rv@4ax.com>:

On Sun, 14 Nov 2021 17:11:29 GMT, Jan Panteltje
pNaOnStPeAlMtje@yahoo.com> wrote:

On a sunny day (Sun, 14 Nov 2021 08:39:13 -0800) it happened
jlarkin@highlandsniptechnology.com wrote in
54e2pgl0ir9ucjhtrcq35c0dj7pkadrgf8@4ax.com>:


Once you have a few resistors on a schematic, it\'s tempting to do what
you want using existing values. That reduces the BOM and the
pick-and-place setup. There are far more possibilities if you are
willing to compromise things some, or put resistors in series and
parallel. This is a 4-page schematic with 9 different resistors. Doing
this is an enormous PITA.

https://www.dropbox.com/s/aozh6m6mmmik6lb/T502_Parts.jpg?raw=1

Saved a DAC reference chip! Actually, having the DAC voltage
ratiometric on +15 is a benefit here.

That opamp should be stable with the tantalum load and a 1u ceramic at
the DAC, but I\'ll verify that.

Or a second LM317 for the +3V?

Yuk! That would involve an entire new chain of value juggling.

Really?


The resistor ratio needs to be 1.4:1. I can get 3.125 volts with three
resistors.

What I do not get is: you sell expensive things in low quantity and try to save on a trimpot?

Trimpots are expensive and need manual turning. DACs are automated and
can have cal factors stored in cal tables. I\'m using 16-bit DACs and
there are no 16-bit trimpots.

Some of my customers absolutely forbid trimpots, which I think is
extreme. Once in a while they make sense. They say that if there\'s a
pot, their techs will turn it.


or waste board space with funny resistor combinations?

I have space on this one for a few more 0603s. It\'s inefficient to
load a reel onto the pick-and-place just for one resistor.

The LM317 is huge.

I mean I use 3 resistors to get a LM317 to output some specific voltage all the time..
mostly different ones.
Sure you can use 1 Ohm resistors to do most things, but then you need many,,,,
10 Ohm would work too here.


The +15 charges a timing ramp through resistors, and the DAC feeds
some timing comparators, so it\'s nice if they are ratiometric. 317\'s
are not very good references.

Data sheets suggest that an LM317 can\'t make 3 volts from 5 volts, so
I\'d have to power it off +24.

Power it from the 15V you made with the first one.


OK, but the little opamp works better. Same number of parts, much
smaller, more stable, uses available values. That\'s the game here.





Pots are your enemy...

--
This email has been checked for viruses by Avast antivirus software.
https://www.avast.com/antivirus

 

[TTman]

On 14/11/2021 18:27, jlarkin@highlandsniptechnology.com wrote:

On Sun, 14 Nov 2021 17:59:06 GMT, Jan Panteltje
pNaOnStPeAlMtje@yahoo.com> wrote:

On a sunny day (Sun, 14 Nov 2021 09:39:03 -0800) it happened
jlarkin@highlandsniptechnology.com wrote in
1ch2pgh4echute3tflmia84j7uosmor4rv@4ax.com>:

On Sun, 14 Nov 2021 17:11:29 GMT, Jan Panteltje
pNaOnStPeAlMtje@yahoo.com> wrote:

On a sunny day (Sun, 14 Nov 2021 08:39:13 -0800) it happened
jlarkin@highlandsniptechnology.com wrote in
54e2pgl0ir9ucjhtrcq35c0dj7pkadrgf8@4ax.com>:


Once you have a few resistors on a schematic, it\'s tempting to do what
you want using existing values. That reduces the BOM and the
pick-and-place setup. There are far more possibilities if you are
willing to compromise things some, or put resistors in series and
parallel. This is a 4-page schematic with 9 different resistors. Doing
this is an enormous PITA.

https://www.dropbox.com/s/aozh6m6mmmik6lb/T502_Parts.jpg?raw=1

Saved a DAC reference chip! Actually, having the DAC voltage
ratiometric on +15 is a benefit here.

That opamp should be stable with the tantalum load and a 1u ceramic at
the DAC, but I\'ll verify that.

Or a second LM317 for the +3V?

Yuk! That would involve an entire new chain of value juggling.

Really?


The resistor ratio needs to be 1.4:1. I can get 3.125 volts with three
resistors.

What I do not get is: you sell expensive things in low quantity and try to save on a trimpot?

Trimpots are expensive and need manual turning. DACs are automated and
can have cal factors stored in cal tables. I\'m using 16-bit DACs and
there are no 16-bit trimpots.

Some of my customers absolutely forbid trimpots, which I think is
extreme. Once in a while they make sense. They say that if there\'s a
pot, their techs will turn it.


or waste board space with funny resistor combinations?

I have space on this one for a few more 0603s. It\'s inefficient to
load a reel onto the pick-and-place just for one resistor.

The LM317 is huge.

I mean I use 3 resistors to get a LM317 to output some specific voltage all the time..
mostly different ones.
Sure you can use 1 Ohm resistors to do most things, but then you need many,,,,
10 Ohm would work too here.


The +15 charges a timing ramp through resistors, and the DAC feeds
some timing comparators, so it\'s nice if they are ratiometric. 317\'s
are not very good references.

Data sheets suggest that an LM317 can\'t make 3 volts from 5 volts, so
I\'d have to power it off +24.

Power it from the 15V you made with the first one.


OK, but the little opamp works better. Same number of parts, much
smaller, more stable, uses available values. That\'s the game here.





Pots are your enemy...

--
This email has been checked for viruses by Avast antivirus software.
https://www.avast.com/antivirus

 

[server]

On Sun, 14 Nov 2021 22:14:47 +0000, TTman <kraken.sankey@gmail.com>
wrote:

On 14/11/2021 18:27, jlarkin@highlandsniptechnology.com wrote:
On Sun, 14 Nov 2021 17:59:06 GMT, Jan Panteltje
pNaOnStPeAlMtje@yahoo.com> wrote:

On a sunny day (Sun, 14 Nov 2021 09:39:03 -0800) it happened
jlarkin@highlandsniptechnology.com wrote in
1ch2pgh4echute3tflmia84j7uosmor4rv@4ax.com>:

On Sun, 14 Nov 2021 17:11:29 GMT, Jan Panteltje
pNaOnStPeAlMtje@yahoo.com> wrote:

On a sunny day (Sun, 14 Nov 2021 08:39:13 -0800) it happened
jlarkin@highlandsniptechnology.com wrote in
54e2pgl0ir9ucjhtrcq35c0dj7pkadrgf8@4ax.com>:


Once you have a few resistors on a schematic, it\'s tempting to do what
you want using existing values. That reduces the BOM and the
pick-and-place setup. There are far more possibilities if you are
willing to compromise things some, or put resistors in series and
parallel. This is a 4-page schematic with 9 different resistors. Doing
this is an enormous PITA.

https://www.dropbox.com/s/aozh6m6mmmik6lb/T502_Parts.jpg?raw=1

Saved a DAC reference chip! Actually, having the DAC voltage
ratiometric on +15 is a benefit here.

That opamp should be stable with the tantalum load and a 1u ceramic at
the DAC, but I\'ll verify that.

Or a second LM317 for the +3V?

Yuk! That would involve an entire new chain of value juggling.

Really?


The resistor ratio needs to be 1.4:1. I can get 3.125 volts with three
resistors.

What I do not get is: you sell expensive things in low quantity and try to save on a trimpot?

Trimpots are expensive and need manual turning. DACs are automated and
can have cal factors stored in cal tables. I\'m using 16-bit DACs and
there are no 16-bit trimpots.

Some of my customers absolutely forbid trimpots, which I think is
extreme. Once in a while they make sense. They say that if there\'s a
pot, their techs will turn it.


or waste board space with funny resistor combinations?

I have space on this one for a few more 0603s. It\'s inefficient to
load a reel onto the pick-and-place just for one resistor.

The LM317 is huge.

I mean I use 3 resistors to get a LM317 to output some specific voltage all the time..
mostly different ones.
Sure you can use 1 Ohm resistors to do most things, but then you need many,,,,
10 Ohm would work too here.


The +15 charges a timing ramp through resistors, and the DAC feeds
some timing comparators, so it\'s nice if they are ratiometric. 317\'s
are not very good references.

Data sheets suggest that an LM317 can\'t make 3 volts from 5 volts, so
I\'d have to power it off +24.

Power it from the 15V you made with the first one.


OK, but the little opamp works better. Same number of parts, much
smaller, more stable, uses available values. That\'s the game here.





Pots are your enemy...

When I see a schematic full of trimpots, it\'s a sure bet that the
author doesn\'t understand things.

The Review Of Scientific Instruments is full of trimpots. And
diffamps. And current mirrors.



--

Father Brown\'s figure remained quite dark and still;
but in that instant he had lost his head. His head was
always most valuable when he had lost it.

 

[server]

On Sun, 14 Nov 2021 22:14:47 +0000, TTman <kraken.sankey@gmail.com>
wrote:

On 14/11/2021 18:27, jlarkin@highlandsniptechnology.com wrote:
On Sun, 14 Nov 2021 17:59:06 GMT, Jan Panteltje
pNaOnStPeAlMtje@yahoo.com> wrote:

On a sunny day (Sun, 14 Nov 2021 09:39:03 -0800) it happened
jlarkin@highlandsniptechnology.com wrote in
1ch2pgh4echute3tflmia84j7uosmor4rv@4ax.com>:

On Sun, 14 Nov 2021 17:11:29 GMT, Jan Panteltje
pNaOnStPeAlMtje@yahoo.com> wrote:

On a sunny day (Sun, 14 Nov 2021 08:39:13 -0800) it happened
jlarkin@highlandsniptechnology.com wrote in
54e2pgl0ir9ucjhtrcq35c0dj7pkadrgf8@4ax.com>:


Once you have a few resistors on a schematic, it\'s tempting to do what
you want using existing values. That reduces the BOM and the
pick-and-place setup. There are far more possibilities if you are
willing to compromise things some, or put resistors in series and
parallel. This is a 4-page schematic with 9 different resistors. Doing
this is an enormous PITA.

https://www.dropbox.com/s/aozh6m6mmmik6lb/T502_Parts.jpg?raw=1

Saved a DAC reference chip! Actually, having the DAC voltage
ratiometric on +15 is a benefit here.

That opamp should be stable with the tantalum load and a 1u ceramic at
the DAC, but I\'ll verify that.

Or a second LM317 for the +3V?

Yuk! That would involve an entire new chain of value juggling.

Really?


The resistor ratio needs to be 1.4:1. I can get 3.125 volts with three
resistors.

What I do not get is: you sell expensive things in low quantity and try to save on a trimpot?

Trimpots are expensive and need manual turning. DACs are automated and
can have cal factors stored in cal tables. I\'m using 16-bit DACs and
there are no 16-bit trimpots.

Some of my customers absolutely forbid trimpots, which I think is
extreme. Once in a while they make sense. They say that if there\'s a
pot, their techs will turn it.


or waste board space with funny resistor combinations?

I have space on this one for a few more 0603s. It\'s inefficient to
load a reel onto the pick-and-place just for one resistor.

The LM317 is huge.

I mean I use 3 resistors to get a LM317 to output some specific voltage all the time..
mostly different ones.
Sure you can use 1 Ohm resistors to do most things, but then you need many,,,,
10 Ohm would work too here.


The +15 charges a timing ramp through resistors, and the DAC feeds
some timing comparators, so it\'s nice if they are ratiometric. 317\'s
are not very good references.

Data sheets suggest that an LM317 can\'t make 3 volts from 5 volts, so
I\'d have to power it off +24.

Power it from the 15V you made with the first one.


OK, but the little opamp works better. Same number of parts, much
smaller, more stable, uses available values. That\'s the game here.





Pots are your enemy...

When I see a schematic full of trimpots, it\'s a sure bet that the
author doesn\'t understand things.

The Review Of Scientific Instruments is full of trimpots. And
diffamps. And current mirrors.



--

Father Brown\'s figure remained quite dark and still;
but in that instant he had lost his head. His head was
always most valuable when he had lost it.

 

[Anthony William Sloman]

On Monday, November 15, 2021 at 9:22:55 AM UTC+11, jla...@highlandsniptechnology.com wrote:

On Sun, 14 Nov 2021 22:14:47 +0000, TTman <kraken...@gmail.com> wrote:
On 14/11/2021 18:27, jla...@highlandsniptechnology.com wrote:
On Sun, 14 Nov 2021 17:59:06 GMT, Jan Panteltje <pNaOnSt...@yahoo.com> wrote:
On a sunny day (Sun, 14 Nov 2021 09:39:03 -0800) it happened jla...@highlandsniptechnology.com wrote in <1ch2pgh4echute3tf...@4ax.com>:
On Sun, 14 Nov 2021 17:11:29 GMT, Jan Panteltje <pNaOnSt...@yahoo.com> wrote:
On a sunny day (Sun, 14 Nov 2021 08:39:13 -0800) it happened jla....@highlandsniptechnology.com wrote in <54e2pgl0ir9ucjhtr...@4ax.com>: \\

<snip>

This is a 4-page schematic with 9 different resistors. Doing this is an enormous PITA.

https://www.dropbox.com/s/aozh6m6mmmik6lb/T502_Parts.jpg?raw=1

It is a pity that the drop-box image doesn\'t show much of the schematic.

<snip>

The resistor ratio needs to be 1.4:1. I can get 3.125 volts with three resistors.

What I do not get is: you sell expensive things in low quantity and try to save on a trimpot?

Trimpots are expensive and need manual turning. DACs are automated and can have cal factors stored in cal tables. I\'m using 16-bit DACs and there are no 16-bit trimpots.

Actually there are, or at least there used to be - Vishay did a rather expensive trim-pot with multiple brushes which was a lot easier to set precisely. I earned a few brownie points with final test by modifying a board which had been a swine to set up by replacing the standard Bournes 18-mm 25 turn trimmer with the Vishay drop in part. What we lost on the expensive part we more than saved on the setting up time.

Some of my customers absolutely forbid trimpots, which I think is extreme. Once in a while they make sense. They say that if there\'s a pot, their techs will turn it.

So do graduate students. Covering the slotted adjusting screw with a blob of epoxy after the pot has been set up can be a wise precaution.

<snip>

Pots are your enemy...

When I see a schematic full of trimpots, it\'s a sure bet that the author doesn\'t understand things.

It isn\'t. The author is showing an understanding of things that John Larkin doesn\'t have to worry about.

> The Review Of Scientific Instruments is full of trimpots. And diffamps. And current mirrors.

The Review of Scientific Instruments published essentially one-off designs to be used by physicists who more or less know what they are doing. The circuits aren\'t designed for volume production. Giving graduate students a trim-pot they can twiddle - under supervision - while watching what happens can help the education process no end, and it is lot less risky that swapping soldered-in select-on-test resistors, particularly when you have an over-confident graduate student doing the soldering.

Differential amplifiers and current mirrors can be useful, and they can look cute. Peer-reviewed science is performance art - the aim is to educate your readers, but you have to get their attention first, so a certain amount of smoke and mirrors (even current mirrors) can be handy. I have published in Rev.Sci. Instrum. (if only rude comments about some of the less impressive circuits) and I do have a cited paper in Measurement Science and Technology so I do know more about this than John Larkin - but probably a whole lot less than Phil Hobbs or Winfield Hill.

--
Bill Sloman, Sydney

 

[Anthony William Sloman]

On Monday, November 15, 2021 at 9:22:55 AM UTC+11, jla...@highlandsniptechnology.com wrote:

On Sun, 14 Nov 2021 22:14:47 +0000, TTman <kraken...@gmail.com> wrote:
On 14/11/2021 18:27, jla...@highlandsniptechnology.com wrote:
On Sun, 14 Nov 2021 17:59:06 GMT, Jan Panteltje <pNaOnSt...@yahoo.com> wrote:
On a sunny day (Sun, 14 Nov 2021 09:39:03 -0800) it happened jla...@highlandsniptechnology.com wrote in <1ch2pgh4echute3tf...@4ax.com>:
On Sun, 14 Nov 2021 17:11:29 GMT, Jan Panteltje <pNaOnSt...@yahoo.com> wrote:
On a sunny day (Sun, 14 Nov 2021 08:39:13 -0800) it happened jla....@highlandsniptechnology.com wrote in <54e2pgl0ir9ucjhtr...@4ax.com>: \\

<snip>

This is a 4-page schematic with 9 different resistors. Doing this is an enormous PITA.

https://www.dropbox.com/s/aozh6m6mmmik6lb/T502_Parts.jpg?raw=1

It is a pity that the drop-box image doesn\'t show much of the schematic.

<snip>

The resistor ratio needs to be 1.4:1. I can get 3.125 volts with three resistors.

What I do not get is: you sell expensive things in low quantity and try to save on a trimpot?

Trimpots are expensive and need manual turning. DACs are automated and can have cal factors stored in cal tables. I\'m using 16-bit DACs and there are no 16-bit trimpots.

Actually there are, or at least there used to be - Vishay did a rather expensive trim-pot with multiple brushes which was a lot easier to set precisely. I earned a few brownie points with final test by modifying a board which had been a swine to set up by replacing the standard Bournes 18-mm 25 turn trimmer with the Vishay drop in part. What we lost on the expensive part we more than saved on the setting up time.

Some of my customers absolutely forbid trimpots, which I think is extreme. Once in a while they make sense. They say that if there\'s a pot, their techs will turn it.

So do graduate students. Covering the slotted adjusting screw with a blob of epoxy after the pot has been set up can be a wise precaution.

<snip>

Pots are your enemy...

When I see a schematic full of trimpots, it\'s a sure bet that the author doesn\'t understand things.

It isn\'t. The author is showing an understanding of things that John Larkin doesn\'t have to worry about.

> The Review Of Scientific Instruments is full of trimpots. And diffamps. And current mirrors.

The Review of Scientific Instruments published essentially one-off designs to be used by physicists who more or less know what they are doing. The circuits aren\'t designed for volume production. Giving graduate students a trim-pot they can twiddle - under supervision - while watching what happens can help the education process no end, and it is lot less risky that swapping soldered-in select-on-test resistors, particularly when you have an over-confident graduate student doing the soldering.

Differential amplifiers and current mirrors can be useful, and they can look cute. Peer-reviewed science is performance art - the aim is to educate your readers, but you have to get their attention first, so a certain amount of smoke and mirrors (even current mirrors) can be handy. I have published in Rev.Sci. Instrum. (if only rude comments about some of the less impressive circuits) and I do have a cited paper in Measurement Science and Technology so I do know more about this than John Larkin - but probably a whole lot less than Phil Hobbs or Winfield Hill.

--
Bill Sloman, Sydney

 

[Anthony William Sloman]

On Monday, November 15, 2021 at 9:22:55 AM UTC+11, jla...@highlandsniptechnology.com wrote:

On Sun, 14 Nov 2021 22:14:47 +0000, TTman <kraken...@gmail.com> wrote:
On 14/11/2021 18:27, jla...@highlandsniptechnology.com wrote:
On Sun, 14 Nov 2021 17:59:06 GMT, Jan Panteltje <pNaOnSt...@yahoo.com> wrote:
On a sunny day (Sun, 14 Nov 2021 09:39:03 -0800) it happened jla...@highlandsniptechnology.com wrote in <1ch2pgh4echute3tf...@4ax.com>:
On Sun, 14 Nov 2021 17:11:29 GMT, Jan Panteltje <pNaOnSt...@yahoo.com> wrote:
On a sunny day (Sun, 14 Nov 2021 08:39:13 -0800) it happened jla....@highlandsniptechnology.com wrote in <54e2pgl0ir9ucjhtr...@4ax.com>: \\

<snip>

This is a 4-page schematic with 9 different resistors. Doing this is an enormous PITA.

https://www.dropbox.com/s/aozh6m6mmmik6lb/T502_Parts.jpg?raw=1

It is a pity that the drop-box image doesn\'t show much of the schematic.

<snip>

The resistor ratio needs to be 1.4:1. I can get 3.125 volts with three resistors.

What I do not get is: you sell expensive things in low quantity and try to save on a trimpot?

Trimpots are expensive and need manual turning. DACs are automated and can have cal factors stored in cal tables. I\'m using 16-bit DACs and there are no 16-bit trimpots.

Actually there are, or at least there used to be - Vishay did a rather expensive trim-pot with multiple brushes which was a lot easier to set precisely. I earned a few brownie points with final test by modifying a board which had been a swine to set up by replacing the standard Bournes 18-mm 25 turn trimmer with the Vishay drop in part. What we lost on the expensive part we more than saved on the setting up time.

Some of my customers absolutely forbid trimpots, which I think is extreme. Once in a while they make sense. They say that if there\'s a pot, their techs will turn it.

So do graduate students. Covering the slotted adjusting screw with a blob of epoxy after the pot has been set up can be a wise precaution.

<snip>

Pots are your enemy...

When I see a schematic full of trimpots, it\'s a sure bet that the author doesn\'t understand things.

It isn\'t. The author is showing an understanding of things that John Larkin doesn\'t have to worry about.

> The Review Of Scientific Instruments is full of trimpots. And diffamps. And current mirrors.

The Review of Scientific Instruments published essentially one-off designs to be used by physicists who more or less know what they are doing. The circuits aren\'t designed for volume production. Giving graduate students a trim-pot they can twiddle - under supervision - while watching what happens can help the education process no end, and it is lot less risky that swapping soldered-in select-on-test resistors, particularly when you have an over-confident graduate student doing the soldering.

Differential amplifiers and current mirrors can be useful, and they can look cute. Peer-reviewed science is performance art - the aim is to educate your readers, but you have to get their attention first, so a certain amount of smoke and mirrors (even current mirrors) can be handy. I have published in Rev.Sci. Instrum. (if only rude comments about some of the less impressive circuits) and I do have a cited paper in Measurement Science and Technology so I do know more about this than John Larkin - but probably a whole lot less than Phil Hobbs or Winfield Hill.

--
Bill Sloman, Sydney

 

[Anthony William Sloman]

On Monday, November 15, 2021 at 9:22:55 AM UTC+11, jla...@highlandsniptechnology.com wrote:

On Sun, 14 Nov 2021 22:14:47 +0000, TTman <kraken...@gmail.com> wrote:
On 14/11/2021 18:27, jla...@highlandsniptechnology.com wrote:
On Sun, 14 Nov 2021 17:59:06 GMT, Jan Panteltje <pNaOnSt...@yahoo.com> wrote:
On a sunny day (Sun, 14 Nov 2021 09:39:03 -0800) it happened jla...@highlandsniptechnology.com wrote in <1ch2pgh4echute3tf...@4ax.com>:
On Sun, 14 Nov 2021 17:11:29 GMT, Jan Panteltje <pNaOnSt...@yahoo.com> wrote:
On a sunny day (Sun, 14 Nov 2021 08:39:13 -0800) it happened jla....@highlandsniptechnology.com wrote in <54e2pgl0ir9ucjhtr...@4ax.com>: \\

<snip>

This is a 4-page schematic with 9 different resistors. Doing this is an enormous PITA.

https://www.dropbox.com/s/aozh6m6mmmik6lb/T502_Parts.jpg?raw=1

It is a pity that the drop-box image doesn\'t show much of the schematic.

<snip>

The resistor ratio needs to be 1.4:1. I can get 3.125 volts with three resistors.

What I do not get is: you sell expensive things in low quantity and try to save on a trimpot?

Trimpots are expensive and need manual turning. DACs are automated and can have cal factors stored in cal tables. I\'m using 16-bit DACs and there are no 16-bit trimpots.

Actually there are, or at least there used to be - Vishay did a rather expensive trim-pot with multiple brushes which was a lot easier to set precisely. I earned a few brownie points with final test by modifying a board which had been a swine to set up by replacing the standard Bournes 18-mm 25 turn trimmer with the Vishay drop in part. What we lost on the expensive part we more than saved on the setting up time.

Some of my customers absolutely forbid trimpots, which I think is extreme. Once in a while they make sense. They say that if there\'s a pot, their techs will turn it.

So do graduate students. Covering the slotted adjusting screw with a blob of epoxy after the pot has been set up can be a wise precaution.

<snip>

Pots are your enemy...

When I see a schematic full of trimpots, it\'s a sure bet that the author doesn\'t understand things.

It isn\'t. The author is showing an understanding of things that John Larkin doesn\'t have to worry about.

> The Review Of Scientific Instruments is full of trimpots. And diffamps. And current mirrors.

The Review of Scientific Instruments published essentially one-off designs to be used by physicists who more or less know what they are doing. The circuits aren\'t designed for volume production. Giving graduate students a trim-pot they can twiddle - under supervision - while watching what happens can help the education process no end, and it is lot less risky that swapping soldered-in select-on-test resistors, particularly when you have an over-confident graduate student doing the soldering.

Differential amplifiers and current mirrors can be useful, and they can look cute. Peer-reviewed science is performance art - the aim is to educate your readers, but you have to get their attention first, so a certain amount of smoke and mirrors (even current mirrors) can be handy. I have published in Rev.Sci. Instrum. (if only rude comments about some of the less impressive circuits) and I do have a cited paper in Measurement Science and Technology so I do know more about this than John Larkin - but probably a whole lot less than Phil Hobbs or Winfield Hill.

--
Bill Sloman, Sydney

 

[whit3rd]

On Sunday, November 14, 2021 at 2:14:53 PM UTC-8, TTman wrote:

On 14/11/2021 18:27, jla...@highlandsniptechnology.com wrote:

I have space on this one for a few more 0603s. It\'s inefficient to
load a reel onto the pick-and-place just for one resistor.

Pots are your enemy...

When mailorder is slow, and you have a triangle file and carbon comp
resistor in play, it\'s time to declare armistice or maybe even peace.

Remember, after filing the notch, to use some nail polish for
sealing that surface... or job it out to a cosmetology shop.

 

[whit3rd]

On Sunday, November 14, 2021 at 2:14:53 PM UTC-8, TTman wrote:

On 14/11/2021 18:27, jla...@highlandsniptechnology.com wrote:

I have space on this one for a few more 0603s. It\'s inefficient to
load a reel onto the pick-and-place just for one resistor.

Pots are your enemy...

When mailorder is slow, and you have a triangle file and carbon comp
resistor in play, it\'s time to declare armistice or maybe even peace.

Remember, after filing the notch, to use some nail polish for
sealing that surface... or job it out to a cosmetology shop.

 

[server]

On Sun, 14 Nov 2021 21:34:51 -0800 (PST), whit3rd <whit3rd@gmail.com>
wrote:

On Sunday, November 14, 2021 at 2:14:53 PM UTC-8, TTman wrote:
On 14/11/2021 18:27, jla...@highlandsniptechnology.com wrote:

I have space on this one for a few more 0603s. It\'s inefficient to
load a reel onto the pick-and-place just for one resistor.

Pots are your enemy...

When mailorder is slow, and you have a triangle file and carbon comp
resistor in play, it\'s time to declare armistice or maybe even peace.

Just buy a few sample kits.



--

Father Brown\'s figure remained quite dark and still;
but in that instant he had lost his head. His head was
always most valuable when he had lost it.

 

[server]

On Sun, 14 Nov 2021 21:34:51 -0800 (PST), whit3rd <whit3rd@gmail.com>
wrote:

On Sunday, November 14, 2021 at 2:14:53 PM UTC-8, TTman wrote:
On 14/11/2021 18:27, jla...@highlandsniptechnology.com wrote:

I have space on this one for a few more 0603s. It\'s inefficient to
load a reel onto the pick-and-place just for one resistor.

Pots are your enemy...

When mailorder is slow, and you have a triangle file and carbon comp
resistor in play, it\'s time to declare armistice or maybe even peace.

Just buy a few sample kits.



--

Father Brown\'s figure remained quite dark and still;
but in that instant he had lost his head. His head was
always most valuable when he had lost it.