Digital potmeter with on/off switch?

Joerg · Apr 17, 2006

Hello Folks,

Is there any device that can not only perform digital potmeter action
with up/down rubber buttons but also replace the power switch? Ideally
suitable up to 20V, automotive or so. However, that 20V could possibly
be done via some regulator.

I am looking into replacing a switch/potmeter combo. It is 1M but lower
values are ok. Main thing is that the whole setup does not consume more
than a few uA in the switched off state.

I know that all this can be accomplished with a uC but this is meant for
a quick demo.

Regards, Joerg

Luhan · Apr 17, 2006

Joerg said:
I am looking into replacing a switch/potmeter combo.

I would suggest simply not doing this; the cost of a pot/switch is only
a few dollars and may be the best solution.

Luhan (low tech) Monat

Joerg · Apr 17, 2006

Hello Luhan,

I would suggest simply not doing this; the cost of a pot/switch is only
a few dollars and may be the best solution.

Well, I wouldn't either. But this is just for a demo, along the lines of
"This is how it would look and feel to a user if...". The real solution
will, of course, be done with a low end uC. Sans crystal, bare bones.

Potmeters are notorious for failures. In most gear they are the number
one items when it comes to QC end test failures or field failures.

Luhan (low tech) Monat

I am a penny pincher myself. I hope this changes when I retire so I
won't go on my wife's nerves too much

Regards, Joerg

Frank Bemelman · Apr 17, 2006

Joerg said:
Hello Folks,

Is there any device that can not only perform digital potmeter action
with up/down rubber buttons but also replace the power switch? Ideally
suitable up to 20V, automotive or so. However, that 20V could possibly
be done via some regulator.

I am looking into replacing a switch/potmeter combo. It is 1M but lower
values are ok. Main thing is that the whole setup does not consume more
than a few uA in the switched off state.

I know that all this can be accomplished with a uC but this is meant for
a quick demo.

Well, all the digital potmeters I've seen had a i2c or SPI or up/dn
control inputs, not suitable for direct pushbutton connections. I'm
afraid you will need a small uC anyway. Maxim has plenty of choice
for digital pots.

I suppose you could make a FF from two cmos nand gates, and power
the uC/pot circuit from one of the outputs, to get that 'few uA when off'.
The 'up' button would always set the FF. The uC can reset the FF,
once the 'down' button has steered the wiper all the way down, and
putting everything to sleep.

Frank Bemelman · Apr 17, 2006

Joerg said:
I am a penny pincher myself. I hope this changes when I retire so I
won't go on my wife's nerves too much

It even works on our nerves sometimes

Joerg · Apr 17, 2006

Hello Frank,

Well, all the digital potmeters I've seen had a i2c or SPI or up/dn
control inputs, not suitable for direct pushbutton connections. I'm
afraid you will need a small uC anyway. Maxim has plenty of choice
for digital pots.

Dallas has some that support direct button connections. They have
de-bounce on board. I have no clue why AD didn't think of that with some
of their digipots.

I suppose you could make a FF from two cmos nand gates, and power
the uC/pot circuit from one of the outputs, to get that 'few uA when off'.
The 'up' button would always set the FF. The uC can reset the FF,
once the 'down' button has steered the wiper all the way down, and
putting everything to sleep.

Currently there is no uC, it's just for a few demo models. I am afraid
I'll have to cook up some logic like usual. I wonder why there is no
product for the typical scenario: Dormant upon power-up, wiper at bottom
and not in the middle like most of them. Hit UP button, unit turns on or
a logic output goes high. Hit UP some more and pot wiper goes upwards.
All that's needed would be a logic output, the rest could be done with
FETs and stuff. Holding the DOWN button long enough would turn it all
off again.

Regards, Joerg

Frank Bemelman · Apr 17, 2006

Currently there is no uC, it's just for a few demo models. I am afraid
I'll have to cook up some logic like usual. I wonder why there is no
product for the typical scenario: Dormant upon power-up, wiper at bottom
and not in the middle like most of them. Hit UP button, unit turns on or
a logic output goes high. Hit UP some more and pot wiper goes upwards.
All that's needed would be a logic output, the rest could be done with
FETs and stuff. Holding the DOWN button long enough would turn it all
off again.

Yes, I see the DS1809 now, that looks okay. Add a 4538 kludge and
you're all done.

BTW, the typical scenario is that users search for an on/off
switch. They panic when they can't find such button

The old potmeter + switch worked, because it also gives the
audible click when turned CCW.

Oh, please add the little speaker that plays "tingel di dum" when
powered on, and "ta di da dom" when powered off

Joerg · Apr 17, 2006

Hello Frank,

Yes, I see the DS1809 now, that looks okay. Add a 4538 kludge and
you're all done.

It'll still be pretty messy and the pot must start at wiper bottom. Most
of these need 5V or some other logic supply which this circuit doesn't
have unless I add some more parts. But I guess this digipot/logic combo
is the only way.

BTW, the typical scenario is that users search for an on/off
switch. They panic when they can't find such button

Just add ON and OFF to the + and - symbols. Or one of those pictograms
that nobody understands ;-)

The old potmeter + switch worked, because it also gives the
audible click when turned CCW.

Oh, please add the little speaker that plays "tingel di dum" when
powered on, and "ta di da dom" when powered off

And offer the capability to download ringtones. For a fee, of course.
Just got a cell phone. It came with six tones, all of them some weird
music stuff and all IMHO pretty disgusting. I guess kids would like this
metallica stuff. They don't even offer a simple beep in there. Arrrgh.

If at least they had that old Radio Noordzee jingle or the one from
Wolfman Jack.

Regards, Joerg

Michael · Apr 18, 2006

Joerg said:
Hello Frank,

It'll still be pretty messy and the pot must start at wiper bottom. Most
of these need 5V or some other logic supply which this circuit doesn't
have unless I add some more parts. But I guess this digipot/logic combo
is the only way.

Just add ON and OFF to the + and - symbols. Or one of those pictograms
that nobody understands ;-)

And offer the capability to download ringtones. For a fee, of course.
Just got a cell phone. It came with six tones, all of them some weird
music stuff and all IMHO pretty disgusting. I guess kids would like this
metallica stuff. They don't even offer a simple beep in there. Arrrgh.

If at least they had that old Radio Noordzee jingle or the one from
Wolfman Jack.

Regards, Joerg

Joerg, if I'm not mistaken a DalSemi digipot can - but does not necessarily -
remember its setting through a power down/up. Whether wiper posn is saved or
not is decided by the implementer (you, in this case). I think this is the
case; it's been forever since I read the datasheet.

I think digipots are cool .... for certain applications. Not for others. I
hated the radio that came with my 1986 Saab because it had no knobs at all. The
day after I took delivery, on a trip from NY to Virginia, I found myself playing
dodge-em with evening rush-hour traffic around Washington D.C. while
simultaneously drilling through the ^%$%#! radio menus to get to the treble/bass
controls! The day after I returned home I ripped that sucker out and dropped it
on the dealer's desk.

Rich Grise · Apr 19, 2006

Hello Luhan,
[Joerg wrote]

I would suggest simply not doing this; the cost of a pot/switch is only
a few dollars and may be the best solution.

Click to expand...

Well, I wouldn't either. But this is just for a demo, along the lines of
"This is how it would look and feel to a user if...". The real solution
will, of course, be done with a low end uC. Sans crystal, bare bones.

If it's just a demo, how important is it to _really_ keep the "off"
current less that a uA, or can you just _tell_ them that it is? (or
will be, of course). Are they going to be measuring it? After all, it's
trivial to implement power-down with a micro, so you'll include that in
the vinal version anyway, right? ;-)

But running a counter up and down with buttons is so trivial - couldn't
you dash off a uP program in an hour or so?

i.e., use a micro for
the demo?

Good Luck!
Rich

Rich Grise · Apr 19, 2006

Hello Frank,
...

Just add ON and OFF to the + and - symbols. Or one of those pictograms
that nobody understands ;-)

And offer the capability to download ringtones. For a fee, of course.
Just got a cell phone. It came with six tones, all of them some weird
music stuff and all IMHO pretty disgusting. I guess kids would like this
metallica stuff. They don't even offer a simple beep in there. Arrrgh.

If at least they had that old Radio Noordzee jingle or the one from
Wolfman Jack.

I'd like to track down a .wav of that unique "ring" tone they used for
the red hot-line phone in "Our Man Flint". Or maybe it was "Dr.
Strangelove". ?:-/

Cheers!
Rich

Joerg · Apr 19, 2006

Hello Rich,

If it's just a demo, how important is it to _really_ keep the "off"
current less that a uA, or can you just _tell_ them that it is? (or
will be, of course). Are they going to be measuring it? After all, it's
trivial to implement power-down with a micro, so you'll include that in
the vinal version anyway, right? ;-)

It is very important. They might take a few with them, leave them on the
shelf for a week and then take them somewhere else. If the battery is
flat by then it would be a major embarrassment. Remember that most of
those feasibility study products will be in the hands of non-EEs.
Whatever you do with feasibility studies you've got to come as close to
the 'real thing' as you can. I am almost there now.

But running a counter up and down with buttons is so trivial - couldn't
you dash off a uP program in an hour or so? i.e., use a micro for
the demo?

Sure, a little MSP430 can do it. But the client that has to show it
needs to be able to play with all the parameters. I can't make them load
the whole IAR Suite, learn how to fiddle with C or assembler source code
and compile and how to rig up the JTAG or serial download. At least not
within a couple of days since they've got other pressing items to tend
to. Nothing beats the ease of swapping a resistor to adjust some timing.
Takes 30 seconds tops.

Regards, Joerg

Joerg · Apr 19, 2006

Hello Michael,

I think digipots are cool .... for certain applications. Not for others. I
hated the radio that came with my 1986 Saab because it had no knobs at all. The
day after I took delivery, on a trip from NY to Virginia, I found myself playing
dodge-em with evening rush-hour traffic around Washington D.C. while
simultaneously drilling through the ^%$%#! radio menus to get to the treble/bass
controls! The day after I returned home I ripped that sucker out and dropped it
on the dealer's desk.

It's not just the radios. I just had a rental car in Phoenix, Toyota
Corolla, same car that my wife is driving except that it was much
younger or 'new and improved'. When I hop into my wife's car I reach for
the rear view and adjust it to my height within two seconds. This one
had an electrified version. I guess that is called progress. Luckily the
person who had the car before me must have been the same height (or gave
up trying to adjust it...). It seemed not to be controlled via the usual
arrow thingie to the left of the steering wheel. That would have been
too simple, wouldn't it?

Regards, Joerg

Jim Thompson · Apr 19, 2006

Hello Michael,

It's not just the radios. I just had a rental car in Phoenix, Toyota
Corolla, same car that my wife is driving except that it was much
younger or 'new and improved'. When I hop into my wife's car I reach for
the rear view and adjust it to my height within two seconds. This one
had an electrified version. I guess that is called progress. Luckily the
person who had the car before me must have been the same height (or gave
up trying to adjust it...). It seemed not to be controlled via the usual
arrow thingie to the left of the steering wheel. That would have been
too simple, wouldn't it?

Regards, Joerg

You mean you couldn't figure out how to program it ?

I love that sort of thing. My wife opens the door on the Q45 and
presses "1" and the seat and mirrors move to her position, except the
seat is pushed back until she sits down and inserts the key, then it
moves forward.

I'm secondary in command, so I press "2" ;-)

...Jim Thompson
--
| James E.Thompson, P.E. | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona Voice

480)460-2350 | |
| E-mail Address at Website Fax

Joerg · Apr 19, 2006

Hello Jim,

You mean you couldn't figure out how to program it ?

Oh, I could have. But when you arrive at 9:00pm and want to meet someone
at a hotel shortly thereafter there ain't much time to crack out the
manuals in the glove compartment. Plus it's dark.

Alamo at PHX was interesting. You aren't assigned a car in a particular
stall but they point you to a group of cars and tell you "Pick one of
these". And your main roads are indeed in better shape than the ones out
here. No pothole dodging. Neighborhoods seem as mixed as here. Filling
up at a gas station on Dobson near 202 my credit card was rejected. The
same one I used to pay at the hotel without a hitch. "See
attendant...". Kind of embarrassing since I had two high-level managers
with me in the car. Turns out the station didn't take cards from
out-of-staters.

I love that sort of thing. My wife opens the door on the Q45 and
presses "1" and the seat and mirrors move to her position, except the
seat is pushed back until she sits down and inserts the key, then it
moves forward.

This can be dangerous if kids are in the car.

Regards, Joerg

Jim Thompson · Apr 19, 2006

Hello Jim,

Oh, I could have. But when you arrive at 9:00pm and want to meet someone
at a hotel shortly thereafter there ain't much time to crack out the
manuals in the glove compartment. Plus it's dark.

I know, I was just razzing you ;-) Had a similar problem with a
big-ass Ford SUV last year in Boston.

Alamo at PHX was interesting. You aren't assigned a car in a particular
stall but they point you to a group of cars and tell you "Pick one of
these".

I've noticed that a number of car rental places are doing that now.

And your main roads are indeed in better shape than the ones out
here. No pothole dodging. Neighborhoods seem as mixed as here. Filling
up at a gas station on Dobson near 202 my credit card was rejected. The
same one I used to pay at the hotel without a hitch. "See
attendant...". Kind of embarrassing since I had two high-level managers
with me in the car. Turns out the station didn't take cards from
out-of-staters.

That's odd. Was it a national card or on a local bank? In my recent
trip to southern California I had no problems. But years ago I did
have problems in Boston with a card from a little Arizona
one-of-a-kind neighborhood bank.

This can be dangerous if kids are in the car.

Regards, Joerg

If kids are in the car they're belted up prior to my/her entrance into
the driver's seat. Plus the "Q" has ample foot-room even with the
seat all the way back... it's not a "toy" car after all ;-)

(And I have the kiddie locks set.)

...Jim Thompson
--
| James E.Thompson, P.E. | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona Voice

480)460-2350 | |
| E-mail Address at Website Fax

Joerg · Apr 19, 2006

Hello Jim,

That's odd. Was it a national card or on a local bank? In my recent
trip to southern California I had no problems. But years ago I did
have problems in Boston with a card from a little Arizona
one-of-a-kind neighborhood bank.

Biggest bank there is. I was puzzled. Possibly they put card readers in
the pumps and then the neighborhood crime rate became too high? The area
looked ok to me. Anyway, the attendant said "Oh no, here you have to
pre-pay". So I left a bill inside and then went back to retrieve the
balance. The only other times I have seen that were in Oakland (CA) and
in Queens (NY). Areas that I'd never visit at night.

Regards, Joerg

Michael · Apr 19, 2006

Joerg said:
Hello Michael,

It's not just the radios. I just had a rental car in Phoenix, Toyota
Corolla, same car that my wife is driving except that it was much
younger or 'new and improved'. When I hop into my wife's car I reach for
the rear view and adjust it to my height within two seconds. This one
had an electrified version. I guess that is called progress. Luckily the
person who had the car before me must have been the same height (or gave
up trying to adjust it...). It seemed not to be controlled via the usual
arrow thingie to the left of the steering wheel. That would have been
too simple, wouldn't it?

Regards, Joerg

Gruess Gott, Joerg

Electric rearview mirrors? What's this world coming to?! I've seen electric
*side* mirrors (sehr gut when weather is sleeting) but not rearview. I guess
the "improvements" are getting harder and harder to dream up, now that cup
holders, individual DVD monitors, zoned climate controls, and-on-and-on are
(probably) standard equipment. Oh! ... and rear-facing video camera; gotta have
*that* (not). I'm not much on cars - I walk or bicycle - so I wouldn't be
surprised if there are even more ridiculous gotta-haves in today's cars.

The Saab radio I wrote about was a Clarion. Great sound, lousy usability, but
with two super features that were sorely missed when I got rid of it: auto scan
tuning; multiple sets of both AM and FM station memories. Happily, fifteen
years later I got a Radio Shack "headset" with those features, on close-out for
just $25.

Jim Thompson · Apr 19, 2006

Hello Jim,

Biggest bank there is. I was puzzled. Possibly they put card readers in
the pumps and then the neighborhood crime rate became too high? The area
looked ok to me. Anyway, the attendant said "Oh no, here you have to
pre-pay". So I left a bill inside and then went back to retrieve the
balance. The only other times I have seen that were in Oakland (CA) and
in Queens (NY). Areas that I'd never visit at night.

Regards, Joerg

480)460-2350 | |
| E-mail Address at Website Fax

Joerg · Apr 20, 2006

Hello Jim,

Dobson/Loop 202 is no garden spot, but I wouldn't think high crime
either. Probably their data link was down.

Maybe but it trundled a while, then asked me for the zip code (that
request must have come via the link). They do this back east, too, but
then the pump opens up.

What surprised me was the instant answer "you can't use that here, got
to pre-pay".

Regards, Joerg

Moore's Lobby Podcast

Menu

Categories

Platforms

Content

Connect With Us

Network

Digital potmeter with on/off switch?

Digital potmeter with on/off switch?

Joerg

Luhan

Joerg

Frank Bemelman

Frank Bemelman

Joerg

Frank Bemelman

Joerg

Michael

Rich Grise

Rich Grise

Joerg

Joerg

Jim Thompson

Joerg

Jim Thompson

Joerg

Michael

Jim Thompson

Joerg

Similar threads