Need a bit of design work done

[Mike Rocket J. Squirrel E]

I'm an analog guy and I need for a bit of logic/adc design work done,
will pay. The design is essentially to sample the voltage on the wiper
of a potentiometer, and use it to drive one of 48 relays, depending on
the wiper voltage. The relays need to be driven in a make-before-break
style. I don't want to run any clocks in the product if at all possible.
Low-speed stuff. I reckon this is digital design 101 as taught in 1980.

Please private mail me for more information if this sounds like
no-brainer stuff to you and you have the time and are interested.

I'm located in Carlsbad, CA.
--
Mike "Rocket J Squirrel" Elliott
71 Type 2: the Wonderbus
84 Westfalia: "Mellow Yellow (The Electrical Banana)"
KG6RCR

 

[Mike Rocket J. Squirrel E]

On 3/29/2005 11:02 PM polleke wrote:

that is very easy one.
Use a multiswitch with a lot of contacts that is the trick. You
will not have to use any electronics only some 1 % resistors.
You also can use a coarse and fine switch as 48 pos switches are
rare.

Of course I would do this if good-feeling 48 position rotary switches
with four decks (stereo balanced signals) were available. The
fine/coarse idea is interesting but not very user-friendly.

--
Mike "Rocket J Squirrel" Elliott
71 Type 2: the Wonderbus
84 Westfalia: "Mellow Yellow (The Electrical Banana)"
KG6RCR

 

[Mike Rocket J. Squirrel E]

On 3/29/2005 6:13 PM nospam wrote:

"Mike Rocket J. Squirrel Elliott"
j.michael.elliottAT@REMOVETHEOBVIOUSgmailDOT.com> wrote:


Oops -- Thanks! (Wrong chip, right family. The LM3914 is the linear one.)


The LM3914 has overlapping comparators and no hysteresis so for some of the
pot you will have one relay on, some of the pot you will have two relays
on, and the rest of the pot you will have one on and one buzzing with the
slightest noise in the system.

Aw fudge.

Clocks and potential interference. The product will be a vacuum-tube
high end audio phono preamplifier.

And I thought is was going to be something sensible like a tapped inductor
for an antenna tuner ;|

Hah. As if. Sensible -- if I wanted to do something sensible I'd have
found another line of work. Or maybe not: I'm going back to college to
get my Master's degree in social work. How sensible is that?


--
--
Mike "Rocket J Squirrel" Elliott
71 Type 2: the Wonderbus
84 Westfalia: "Mellow Yellow (The Electrical Banana)"
KG6RCR

 

[nospam]

"Mike Rocket J. Squirrel Elliott"
<j.michael.elliottAT@REMOVETHEOBVIOUSgmailDOT.com> wrote:

Clocks and potential interference. The product will be a vacuum-tube
high end audio phono preamplifier.

And I thought is was going to be something sensible like a tapped inductor
for an antenna tuner ;|

Hah. As if. Sensible -- if I wanted to do something sensible I'd have
found another line of work. Or maybe not: I'm going back to college to
get my Master's degree in social work. How sensible is that?

Well high end audio is more of a social than electronic phenomena.

If you insist on a non-processor solution I think I would use a 6 bit
up/down counter clocked at a few Hz. Drive a DAC from the counter and
slightly tricky dual comparators compare its output with a voltage from the
pot. The comparators will produce up/down enables for the counter.

That would take about 5 chips and give you a 6 bit binary code which tracks
the pot with no missing counts and a defined maximum slew rate.

The make before break is tricky and perhaps depends on how you can drive
the relays.

7 off 3 to 8 line decoders like the 4051 will give you one of 48 outputs
from a 6 bit code.

If the relays need drivers then integrating an R/C turn off delay on each
driver might be the simplest. If the relays can be driven by 'logic' then
it may be simpler to have two 6 to 48 line decoders driving the relays, one
from the up/down counter and another from a latched copy of the counter
delayed by one clock.

 

[Mike Rocket J. Squirrel E]

On 3/30/2005 3:26 PM nospam wrote:

"Mike Rocket J. Squirrel Elliott"
j.michael.elliottAT@REMOVETHEOBVIOUSgmailDOT.com> wrote:


Clocks and potential interference. The product will be a vacuum-tube
high end audio phono preamplifier.



And I thought is was going to be something sensible like a tapped inductor
for an antenna tuner ;|


Hah. As if. Sensible -- if I wanted to do something sensible I'd have
found another line of work. Or maybe not: I'm going back to college to
get my Master's degree in social work. How sensible is that?


Well high end audio is more of a social than electronic phenomena.

If you insist on a non-processor solution I think I would use a 6 bit
up/down counter clocked at a few Hz. Drive a DAC from the counter and
slightly tricky dual comparators compare its output with a voltage from the
pot. The comparators will produce up/down enables for the counter.

That would take about 5 chips and give you a 6 bit binary code which tracks
the pot with no missing counts and a defined maximum slew rate.

The make before break is tricky and perhaps depends on how you can drive
the relays.

7 off 3 to 8 line decoders like the 4051 will give you one of 48 outputs
from a 6 bit code.

If the relays need drivers then integrating an R/C turn off delay on each
driver might be the simplest. If the relays can be driven by 'logic' then
it may be simpler to have two 6 to 48 line decoders driving the relays, one
from the up/down counter and another from a latched copy of the counter
delayed by one clock.

I'd like to reply to this privately -- please drop me a note to my
e-mail address.

--
--
Mike "Rocket J Squirrel" Elliott
71 Type 2: the Wonderbus
84 Westfalia: "Mellow Yellow (The Electrical Banana)"
KG6RCR

 

[Tony Williams]

In article <zrGdnan-KMNxPNTfRVn-2Q@adelphia.com>,
Mike Rocket J. Squirrel Elliott

Hmmm. I like the way you think! Does anyone make IC's with
multiple window comparators with something like one-pin control
of hysteresis . . . ?

This is a repost of a post that didn't seem to make it.

A 6-bit flash ADC has the required comparators and
no clock.

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.

--
Tony Williams.

 

[Mike Rocket J. Squirrel E]

On 4/1/2005 8:04 AM bill.sloman@ieee.org wrote:

Mike Rocket J. Squirrel Elliott wrote:

On 3/29/2005 2:50 PM Helmut Sennewald wrote:


"Mike Rocket J. Squirrel Elliott"
j.michael.elliottAT@REMOVETHEOBVIOUSgmailDOT.com> schrieb im

Newsbeitrag

newsPmdnd2iT_QmKdTfRVn-pw@adelphia.com...


On 3/29/2005 10:43 AM Mike Rocket J. Squirrel Elliott wrote:



On 3/29/2005 3:08 AM Robert Baer wrote:



Mike Rocket J. Squirrel Elliott wrote:



I'm an analog guy and I need for a bit of logic/adc design work

done,

will pay. The design is essentially to sample the voltage on the

wiper

of a potentiometer, and use it to drive one of 48 relays,

depending on

the wiper voltage. The relays need to be driven in a

make-before-break

style. I don't want to run any clocks in the product if at all
possible. Low-speed stuff. I reckon this is digital design 101

as

taught in 1980.

Please private mail me for more information if this sounds like
no-brainer stuff to you and you have the time and are

interested.

I'm located in Carlsbad, CA.

Oops -- Thanks! (Wrong chip, right family. The LM3914 is the linear

one.)

I don't know how to write code, so programming a uC would require

paying

someone for that. And buying hardware to program the uC. I can't

debug

code, either, so I would need to keep bothering the programmer. I've

had

difficulty in the past with code that needed debugging a couple years


later, only to find that the programmer guy was no longer available.

A

hardware implementation, like this simple IC approach, is something I


can understand and debug myself. I guess I prefer to do things myself

if

possible using technology even I can understand.

Clocks and potential interference. The product will be a vacuum-tube
high end audio phono preamplifier. I personally don't think that

having

an oscillator in this product will be a problem with halfway decent
shielding. But the marketplace will have more trust in the product if

it

is dead quiet (EMI-wise) inside. High-end audio is odd that way. Far
easier to not build in a perceived problem then try to defend

challenges

later.


Have you thought about using a rotary encoder?

Rotary encoders don't provide visual feedback about there the volume is
set. A regular old potentiometer is generally connected to a knob, and
the knob generally has a pointer. One can glance at the pointer to see
where the volume is set before pushing "play" on the CD player, or
lowering the stylus onto the record. All the rotary encoders I've ever
seen go 'round and 'round w/o any real reference and w/o any pointer.
The only way that I know of to provide visual feedback about where the
volume is set when using a rotary encoder is with a display of some
sort, generally a VFL dot-matrix thingy, which requires a micro to run
and lots of other things to sort out.

As always, I could be wrong.
--
Mike "Rocket J Squirrel" Elliott
71 Type 2: the Wonderbus
84 Westfalia: "Mellow Yellow (The Electrical Banana)"
KG6RCR

 

[Tony Williams]

In article <4d5430173dtonyw@ledelec.demon.co.uk>,
Tony Williams <tonyw@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.

--
Tony Williams.

 

[Bill Sloman]

"Tony Williams" <tonyw@ledelec.demon.co.uk> schreef in bericht
news:4d55b0d8fetonyw@ledelec.demon.co.uk...

In article <4d5430173dtonyw@ledelec.demon.co.uk>,
Tony Williams <tonyw@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.

For strictly sequential selection you can fix this by adding extra lines
(view with a fixed width font, like Courier)

1 3 5 7 9 11 13 15
17 19 21 23 25 27 29 31
33 35 37 39 41 43 45 47

2 4 6 8 10 12 14 16
18 20 22 24 26 28 30 32
34 36 38 40 42 44 46 48

The number of drivers required rises from 14 (6x8) for 48 relays, to 16
(6x10) . I like the division into two blocks of odd an even relays - I
expect that it would make the logic simpler.

With this arrangment, when you need to select two row and two columns, the
two extra intersections selected are empty.

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.

That would work too, and wouldn't require fancy logic .....

Bill Sloman, Nijmegen

 

[Chuck Harris]

Tony Williams wrote:

In article <4d5430173dtonyw@ledelec.demon.co.uk>,
Tony Williams <tonyw@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.

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.

-Chuck

 

[Mark Borgerson]

In article <4d55b0d8fetonyw@ledelec.demon.co.uk>,
tonyw@ledelec.demon.co.uk says...

In article <4d5430173dtonyw@ledelec.demon.co.uk>,
Tony Williams <tonyw@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?


Mark Borgerson

 

[Mike Rocket J. Squirrel E]

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

In article <4d55b0d8fetonyw@ledelec.demon.co.uk>,
tonyw@ledelec.demon.co.uk says...

In article <4d5430173dtonyw@ledelec.demon.co.uk>,
Tony Williams <tonyw@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."

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.

--
Mike "Rocket J Squirrel" Elliott
71 Type 2: the Wonderbus
84 Westfalia: "Mellow Yellow (The Electrical Banana)"
KG6RCR

 

[Mike Rocket J. Squirrel E]

On 4/3/2005 9:03 AM Chuck Harris wrote:

Tony Williams wrote:

In article <4d5430173dtonyw@ledelec.demon.co.uk>,
Tony Williams <tonyw@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.


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

No problem. Think about the volume control on a stereo -- it's rare that
someone will grab it and wrench it from one extreme to another, most
motions are more deliberate.

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
71 Type 2: the Wonderbus
84 Westfalia: "Mellow Yellow (The Electrical Banana)"
KG6RCR

 

[Chuck Harris]

Chuck Harris wrote:

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.

It occurs to me, that I can even do the job with just one pic, and no extra
relay drivers, and just a dozen back EMF diodes.

The magic of software!

-Chuck

 

[Tony Williams]

In article <_46dnR4qh5l7js3fRVn-sQ@rcn.net>,
Chuck Harris <cf-NO-SPAM-harris@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.

--
Tony Williams.

 

[Mark Borgerson]

In article <1112636001.110071.183040@l41g2000cwc.googlegroups.com>,
spamgoeshere4@yahoo.com says...

Tony Williams wrote:
In article <_46dnR4qh5l7js3fRVn-sQ@rcn.net>,
Chuck Harris <cf-NO-SPAM-harris@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

shut off all the clocks until an interrupt. That interrupt could be
from a pin level change on the bits from an optical encoder.
After the level change, you could latch whatever bits are needed
for the visual feedback display and relays, and have the MCU
go back to sleep.


Mark Borgerson

 

[Mike Rocket J. Squirrel E]

On 4/2/2005 4:17 AM bill.sloman@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
71 Type 2: the Wonderbus
84 Westfalia: "Mellow Yellow (The Electrical Banana)"
KG6RCR

 

[Mike Rocket J. Squirrel E]

On 4/4/2005 3:25 PM bill.sloman@ieee.org wrote:

Mike Rocket J. Squirrel Elliott wrote:

On 4/2/2005 4:17 AM bill.sloman@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.

Oh -- the empirical approach. Right.

--

Mike "Rocket J Squirrel" Elliott
71 Type 2: the Wonderbus
84 Westfalia: "Mellow Yellow (The Electrical Banana)"
KG6RCR

 

[Mike Rocket J. Squirrel E]

On 4/5/2005 2:01 AM bill.sloman@ieee.org wrote:

Mike Rocket J. Squirrel Elliott wrote:

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


In article <Ab2dnZGatI8yBM3fRVn-uw@adelphia.com>,
j.michael.elliottAT@REMOVETHEOBVIOUSgmailDOT.com says...


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



In article <4d55b0d8fetonyw@ledelec.demon.co.uk>,
tonyw@ledelec.demon.co.uk says...



In article <4d5430173dtonyw@ledelec.demon.co.uk>,
Tony Williams <tonyw@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

Okay, it's an interesting approach which solves many of the problems . .
.. and I appreciate the brain power you put into it. The names for the
ranges are especially noteworthy.

(Is the market ready for a 4-speed manual volume control?)

--
Mike "Rocket J Squirrel" Elliott
71 Type 2: the Wonderbus
84 Westfalia: "Mellow Yellow (The Electrical Banana)"
KG6RCR

 

[Chuck Harris]

Mike Rocket J. Squirrel Elliott wrote:

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.

Hi Mike,

There are easy ways to work, and hard ways to work. I could design the
system using 48 comparitors, and 48 precision resistors, and a passel of
relay drivers, and a little magic to make the relays make before break.
The board would take a bunch of chips, and would offer plenty of opportunities
for failure.

.... or, I could design a simple processor based solution that would take
one chip that would do the A-to-D, and the overlapping switching, and then
use a mux, and a pile of relay drivers to fan out to all of the relays.

.... 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.

As to programming microprocessors, I always give the code to the customer
simply because it is the right thing to do. And I can program as many of
the parts as needed as part of the contract.

-Chuck