Need a bit of design work done

The better solution is to use some logic, perhaps a small
microprocessor that has an A-to-D converter built in, and
has a clock that is entirely contained within the wafer of
the chip.


Well, if it's just not possible to do this with non-clocked logic, then
that's pretty much the way I will necessarily go, but I do want to make
certain that I am not overlooking an approach that a. doesn't have a
clock and b. won't require someone smarter than me to write the code. As
mentioned earlier in this (long) thread, I have in the past found myself
using uP's programmed by someone who has dropped out of sight, taking
the source code with him.

Mike Rocket J. Squirrel Elliott wrote:

... or I can use two PICS to give you the 48 control lines, and if you
are using
reasonable 5V relays, I would need only some diodes to protect the
drivers from
the relay's back EMF. The pics form their own oscillators, and can drive
the relays directly. A two chip solution. The program would only be a
couple
of lines of "C" code.

On 4/3/2005 12:28 PM Mark Borgerson wrote:

In article <4d55b0d8fetonyw_at_ledelec.demon.co.uk>,
tonyw_at_ledelec.demon.co.uk says...

In article <4d5430173dtonyw_at_ledelec.demon.co.uk>,
Tony Williams <tonyw_at_ledelec.demon.co.uk> wrote:


Send the 6-bit output (1 of 64) into 2x 3-8 line
decoders. Arrange the 48 relays into a 6x8 matrix,
with 6x high-side relay drivers and 8x low-side.

Get the make-before-break by slugging the OFF of
each relay...... perhaps with 14x R+C gated gates
before the row and column relay drivers.

Followup.....

There's a problem when trying to do make-before-break
with a matrix. Overlap of two relays is ok until the
selection of the next relay requires a change to both
a new row and column. Two rows and two columns being
active will result in 4 relays being energised.

The only solution I can see is to have an R+C across
each relay. Around about 100 ohms and 47uF will do a
5-10mS holdup.



I presume that you mean to place the R+C across the input
to the relay driver. Placing substantial resistance
and capacitance near the actual relay coils, with their
low resistance and high inductance, sounds like a problem
looking for a place to happen.


It all seems a bit of overkill when you could simply buy
a 46-position stepped attenuator from Marchand Electronics

http://www.marchandelec.com/att.html

Or are you trying to compete with them by offering an
extra two steps?


No, no competing. I've tried those Shallco/Shallcross rotary switches
before and they don't offer a very good "feel."
However, your system makes the electrical connections, the 'feel' is

But I think I owe an apology to all here on sci.electronics.cad -- my
original post was just a solicitation for assistance on this design, to
be taken off-line and done privately. I had not intended to chew up
bandwidth with a non-CAD thread. So to anyone who's gotten a little
tired of this, I apologize for the inconvenience.

Only works if you can predefine the rate the pot is turned.

The better solution is to use some logic, perhaps a small
microprocessor that has an A-to-D converter built in, and
has a clock that is entirely contained within the wafer of
the chip.

Tony Williams wrote:
In article <_46dnR4qh5l7js3fRVn-sQ_at_rcn.net>,
Chuck Harris <cf-NO-SPAM-harris_at_erols.com> wrote:

Only works if you can predefine the rate the pot is turned.

There is a requirement for make before break on the
relays which inherently sets the maximum change rate.

A little comms relay will take not more than about
2 to 3 mS to close. Assume that 48 relays represent
1 full turn of the pot. So that would be about 100
to 140 mS end-end, or equivalent to about 500 rpm.

The better solution is to use some logic, perhaps a small
microprocessor that has an A-to-D converter built in, and
has a clock that is entirely contained within the wafer of
the chip.

A 40 pin PIC with ADC would certainly do the job,
probably allowing Bill's out-of-sequence delayed
matrix driver to be implemented in software.

Software has the advantage of being able to do
extra performance enhancers, without additional
(and expensive) hardware. For example, putting
in a small amount of hysteresis, so that there
is no relay chatter at the switchover points.

The OP said no clocks, but I just realized that a small MCU can use an
entirely internal clock which would produce very, very little in the
way of EMI which is what the "No Clock" requirement is about. Once you
go with an MCU with a clock rate 1000x the relay rate, you can do
pretty much anything you want in software.

BTW, the EMI issue is normally only when the pot is not being turned.
My experience with high end audio is that adjustments like this are
only used when no recording is being done. Clearly the relays make
more EMI than a dozen MCUs with external clocks. But the relays only
change when you twirl the knobs. The MCU clock runs all the time.


Does the clock have to run all the time? I thought some MCUs could

In article <_46dnR4qh5l7js3fRVn-sQ_at_rcn.net>,
Chuck Harris <cf-NO-SPAM-harris_at_erols.com> wrote:

Only works if you can predefine the rate the pot is turned.

There is a requirement for make before break on the
relays which inherently sets the maximum change rate.

A little comms relay will take not more than about
2 to 3 mS to close. Assume that 48 relays represent
1 full turn of the pot. So that would be about 100
to 140 mS end-end, or equivalent to about 500 rpm.

The better solution is to use some logic, perhaps a small
microprocessor that has an A-to-D converter built in, and
has a clock that is entirely contained within the wafer of
the chip.

A 40 pin PIC with ADC would certainly do the job,
probably allowing Bill's out-of-sequence delayed
matrix driver to be implemented in software.

Software has the advantage of being able to do
extra performance enhancers, without additional
(and expensive) hardware. For example, putting
in a small amount of hysteresis, so that there
is no relay chatter at the switchover points.

Then you want an absolute rotary encoder, like the Bourns part I
mentioned.

http://www.bourns.com/pdfs/ACE.pdf

Put a collet knob with a pointer or a dot on the shaft of the encoder,
and make sure that the shaft is sitting in the right place before you
lock the knob onto the shaft by tightening the collet, and you've got
your display and memory.

The running torque is specified as between 0.5 to 1.5 newton-cm (0.75
to 2.5 ounce-inches) so it should stay put if you don't explicitly turn
it.

In article <Ab2dnZGatI8yBM3fRVn-uw_at_adelphia.com>,
j.michael.elliottAT_at_REMOVETHEOBVIOUSgmailDOT.com says...

On 4/3/2005 12:28 PM Mark Borgerson wrote:


In article <4d55b0d8fetonyw_at_ledelec.demon.co.uk>,
tonyw_at_ledelec.demon.co.uk says...


In article <4d5430173dtonyw_at_ledelec.demon.co.uk>,
Tony Williams <tonyw_at_ledelec.demon.co.uk> wrote:



Send the 6-bit output (1 of 64) into 2x 3-8 line
decoders. Arrange the 48 relays into a 6x8 matrix,
with 6x high-side relay drivers and 8x low-side.

Get the make-before-break by slugging the OFF of
each relay...... perhaps with 14x R+C gated gates
before the row and column relay drivers.

Followup.....

There's a problem when trying to do make-before-break
with a matrix. Overlap of two relays is ok until the
selection of the next relay requires a change to both
a new row and column. Two rows and two columns being
active will result in 4 relays being energised.

The only solution I can see is to have an R+C across
each relay. Around about 100 ohms and 47uF will do a
5-10mS holdup.



I presume that you mean to place the R+C across the input
to the relay driver. Placing substantial resistance
and capacitance near the actual relay coils, with their
low resistance and high inductance, sounds like a problem
looking for a place to happen.


It all seems a bit of overkill when you could simply buy
a 46-position stepped attenuator from Marchand Electronics

http://www.marchandelec.com/att.html

Or are you trying to compete with them by offering an
extra two steps?


No, no competing. I've tried those Shallco/Shallcross rotary switches
before and they don't offer a very good "feel."

However, your system makes the electrical connections, the 'feel' is
going to be an element of the mechanical design of the switches and
detents. Perhaps this is an issue for a mechanical engineer rather
than an electrical engineer.

It may definitely be easier to get a good 'feel' if you divide your 48
steps up into 3 revolutions of 16 steps with an electronic indicator.
That isn't easily done with a simple rotary switch.

On 4/2/2005 4:17 AM bill.sloman_at_ieee.org wrote:

Then you want an absolute rotary encoder, like the Bourns part I
mentioned.

http://www.bourns.com/pdfs/ACE.pdf

Put a collet knob with a pointer or a dot on the shaft of the
encoder,
and make sure that the shaft is sitting in the right place before
you
lock the knob onto the shaft by tightening the collet, and you've
got
your display and memory.

The running torque is specified as between 0.5 to 1.5 newton-cm
(0.75
to 2.5 ounce-inches) so it should stay put if you don't explicitly
turn
it.

Does anyone know how to translate a torque spec like this into how a
knob "feels"? On a proper bit of high-end audio, the knobs want to
feel
silky with a bit of resistance, like they are damped with heavy
grease.
A knob that is too hard to turn, feels gritty or rough, or spins like
a
pinwheel with little or no resistance is likely to raise eyebrows.
Raised eyebrows: bad!

Mike Rocket J. Squirrel Elliott wrote:

On 4/2/2005 4:17 AM bill.sloman_at_ieee.org wrote:


Then you want an absolute rotary encoder, like the Bourns part I
mentioned.

http://www.bourns.com/pdfs/ACE.pdf

Put a collet knob with a pointer or a dot on the shaft of the

encoder,

and make sure that the shaft is sitting in the right place before

you

lock the knob onto the shaft by tightening the collet, and you've

got

your display and memory.

The running torque is specified as between 0.5 to 1.5 newton-cm

(0.75

to 2.5 ounce-inches) so it should stay put if you don't explicitly

turn

it.

Does anyone know how to translate a torque spec like this into how a
knob "feels"? On a proper bit of high-end audio, the knobs want to

feel

silky with a bit of resistance, like they are damped with heavy

grease.

A knob that is too hard to turn, feels gritty or rough, or spins like

a

pinwheel with little or no resistance is likely to raise eyebrows.
Raised eyebrows: bad!


Buy one and find out.

On 4/3/2005 8:45 PM Mark Borgerson wrote:

In article <Ab2dnZGatI8yBM3fRVn-uw_at_adelphia.com>,
j.michael.elliottAT_at_REMOVETHEOBVIOUSgmailDOT.com says...

On 4/3/2005 12:28 PM Mark Borgerson wrote:


In article <4d55b0d8fetonyw_at_ledelec.demon.co.uk>,
tonyw_at_ledelec.demon.co.uk says...


In article <4d5430173dtonyw_at_ledelec.demon.co.uk>,
Tony Williams <tonyw_at_ledelec.demon.co.uk> wrote:



Send the 6-bit output (1 of 64) into 2x 3-8 line
decoders. Arrange the 48 relays into a 6x8 matrix,
with 6x high-side relay drivers and 8x low-side.

Get the make-before-break by slugging the OFF of
each relay...... perhaps with 14x R+C gated gates
before the row and column relay drivers.

Followup.....

There's a problem when trying to do make-before-break
with a matrix. Overlap of two relays is ok until the
selection of the next relay requires a change to both
a new row and column. Two rows and two columns being
active will result in 4 relays being energised.

The only solution I can see is to have an R+C across
each relay. Around about 100 ohms and 47uF will do a
5-10mS holdup.



I presume that you mean to place the R+C across the input
to the relay driver. Placing substantial resistance
and capacitance near the actual relay coils, with their
low resistance and high inductance, sounds like a problem
looking for a place to happen.


It all seems a bit of overkill when you could simply buy
a 46-position stepped attenuator from Marchand Electronics

http://www.marchandelec.com/att.html

Or are you trying to compete with them by offering an
extra two steps?


No, no competing. I've tried those Shallco/Shallcross rotary
switches
before and they don't offer a very good "feel."

However, your system makes the electrical connections, the 'feel'
is
going to be an element of the mechanical design of the switches and
detents. Perhaps this is an issue for a mechanical engineer rather
than an electrical engineer.

That's why I want to use a good-feeling potentiometer for the
control.
They are easily found in small quantities, whereas multiple-position
rotary switches with a good "feel" -- once you get past 20 or so
positions -- are not. Designing a custom switch for this application
is
not feasible due to the very small quantities of units to be made.

It may definitely be easier to get a good 'feel' if you divide your
48
steps up into 3 revolutions of 16 steps with an electronic
indicator.
That isn't easily done with a simple rotary switch.

Well . . . I see what you are saying . . . but, um. . . . I dunno.
Let's
see: A 16-step rotary switch that goes from fully CCW to CW, and a
"low," "middle" "high" switch. To ramp the volume up you might start
in
"first gear," crank the knob all the way up, then shift to "second
gear," while cranking the revs . . . I mean the knob back down . . .
I
can see my wife facing such a thing: "I don't drive a stick."

And what if the average range you like is in between step 15 of the
middle range and step 2 of the high range. That could prove to be a
hassle what with knob twisting and range switching all the time.

You glance at a volume control knob and note it is at 12 o' clock.
You
know how loud that is (generally -- after a bit of time with any
system
you get a feel for how the knob pointer relates to sound level).
Automatic transmission operation.

Mike Rocket J. Squirrel Elliott wrote:

On 4/3/2005 8:45 PM Mark Borgerson wrote:


In article <Ab2dnZGatI8yBM3fRVn-uw_at_adelphia.com>,
j.michael.elliottAT_at_REMOVETHEOBVIOUSgmailDOT.com says...


On 4/3/2005 12:28 PM Mark Borgerson wrote:



In article <4d55b0d8fetonyw_at_ledelec.demon.co.uk>,
tonyw_at_ledelec.demon.co.uk says...



In article <4d5430173dtonyw_at_ledelec.demon.co.uk>,
Tony Williams <tonyw_at_ledelec.demon.co.uk> wrote:




Send the 6-bit output (1 of 64) into 2x 3-8 line
decoders. Arrange the 48 relays into a 6x8 matrix,
with 6x high-side relay drivers and 8x low-side.

Get the make-before-break by slugging the OFF of
each relay...... perhaps with 14x R+C gated gates
before the row and column relay drivers.

Followup.....

There's a problem when trying to do make-before-break
with a matrix. Overlap of two relays is ok until the
selection of the next relay requires a change to both
a new row and column. Two rows and two columns being
active will result in 4 relays being energised.

The only solution I can see is to have an R+C across
each relay. Around about 100 ohms and 47uF will do a
5-10mS holdup.



I presume that you mean to place the R+C across the input
to the relay driver. Placing substantial resistance
and capacitance near the actual relay coils, with their
low resistance and high inductance, sounds like a problem
looking for a place to happen.


It all seems a bit of overkill when you could simply buy
a 46-position stepped attenuator from Marchand Electronics

http://www.marchandelec.com/att.html

Or are you trying to compete with them by offering an
extra two steps?


No, no competing. I've tried those Shallco/Shallcross rotary

switches

before and they don't offer a very good "feel."

However, your system makes the electrical connections, the 'feel'

is

going to be an element of the mechanical design of the switches and
detents. Perhaps this is an issue for a mechanical engineer rather
than an electrical engineer.

That's why I want to use a good-feeling potentiometer for the

control.

They are easily found in small quantities, whereas multiple-position
rotary switches with a good "feel" -- once you get past 20 or so
positions -- are not. Designing a custom switch for this application

is

not feasible due to the very small quantities of units to be made.


It may definitely be easier to get a good 'feel' if you divide your

48

steps up into 3 revolutions of 16 steps with an electronic

indicator.

That isn't easily done with a simple rotary switch.

Well . . . I see what you are saying . . . but, um. . . . I dunno.

Let's

see: A 16-step rotary switch that goes from fully CCW to CW, and a
"low," "middle" "high" switch. To ramp the volume up you might start

in

"first gear," crank the knob all the way up, then shift to "second
gear," while cranking the revs . . . I mean the knob back down . . .

I

can see my wife facing such a thing: "I don't drive a stick."

And what if the average range you like is in between step 15 of the
middle range and step 2 of the high range. That could prove to be a
hassle what with knob twisting and range switching all the time.

You glance at a volume control knob and note it is at 12 o' clock.

You

know how loud that is (generally -- after a bit of time with any

system

you get a feel for how the knob pointer relates to sound level).
Automatic transmission operation.


A four postion coarse switch - "quiet", "clear","emphatic" and "loud"
-would allow you to overlap your ranges - say

1-16
11-27
22-37
33-48