retrofitting an auto-mute volume control?
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From: ehsjr on 14 Dec 2009 12:27 Jon Kirwan wrote: > On Sun, 13 Dec 2009 22:47:39 -0500, ehsjr wrote: > > >>Jon Kirwan wrote: >> >>><snip> >>>Do I get the gist so far? >> >>Yes, I think you understand it. The hysteresis does what you said, but >>it was more to make the trigger "window" a little wider, and make the >>switching crisp and definite. As far as moving the control in either >>direction, it is solvable as you said. Maybe use a second comparator >>set up to switch when the control moves in the other direction. As >>far as muting, use the comparator output(s) to reset the timer, and >>the timer output to switch the audio output line from the speaker(s) >>to a resistor or resistors and vice versa. >> >>Regarding the existing pot setup, it is often like this, >>where the signal comes from the preamp: >> Signal---[cap]---+ >> | >> P >> O<---- signal out to amplifier stage >> T >> | >> Gnd -------------+ > > > Yes. I anticipate this _after_ the first stage's conditioning of the > input and well before the final power stage. > > Suppose that the 'signal out' you mention passes through yet another > cap before the next stage. If so, isn't this a problem for a DC path? > > || C1 > IN --------||-----, > || | > | > \ > Rx / || > \ <----||----- OUT > / || C2 > \ > | > | > --- > /// > > No DC current path, right? > > In any case, I just opened up my first victim. The pot has 7 points > of attachment into the PC board. Two of them are twist tabs for the > main mounting and are themselves grounded. Of the other five, they > are on 5-hole line tangent at the circumference. One of these is tied > to the same ground. But the other four 'go somewhere'. > > Call the pins A, B, C, D, and E. Pin B is tied to the negative rail > (ground.) (Since there is a battery system, as well as AC, I can > verify that it is the most negative rail by using the most negative > side of the battery pack connection.) > > Here are the measurements against ground for two rotation positions: > > MIN VOL MAX VOL > --------------------------- > A 0.5 ohm 32.3k ohm > B --- --- > C 0.5 ohm 32.3k ohm > D 220 ohm 32.3k ohm > E 47.7k ohm 32.3k ohm > > Obviously, in-circuit and not desoldered. Interestingly, the > resistance between A and C goes from about 0 ohms to about 64.5k ohms > going from MIN to MAX volume, respectively. The resistance from C to > D goes from 220 ohms to 0 ohms going from MIN to MAX, respectively. > > That's enough to make this interesting. I need to think more closely > to be sure, but the pot appears to not be a single resistor track and > wiper, at first blush. > > I think I need to assume every other system will be just as messy. > Then, at least, the only way is down -- easier -- from there. > > >>>Another issue is what mutes the output. If I actively mute, that act >>>itself will affect what those same nodes do for the comparator inputs >>>(filtered and unfiltered) since those nodes must be involved in the >>>muting, itself. That presents a possible problem. What I may like to >>>do is separate things so that I isolate the pot and 'copy' its value >>>to the prior nodes being controlled. Well, that gives me some thought >>>lines to move along. >> >>It should't affect the comparators if it occurs between the final >>amplifier and the speaker(s). > > > I have a hard time imagining a pot right at the final stage, because > of the power (few watts, at least) involved. But you might be talking > about something else I said. > > >>>Possible variations are discrete circuits, IC circuits, and a host of >>>topologies to ferret out and design around. Maybe the best way to >>>start is to just start. I'll open up one of the devices and see what >>>I see there. >> >>Good luck! > > > Thanks. Looks like I'm going to need it. Blasted thing. > > Jon Hi Jon, Usually the pot is early in the audio chain, between the preamp and the power amp stage, something like this: input===>preamp===>pot===ground | +===>power amp======>speaker Regarding the following: > || C1 > IN --------||-----, > || | > | > \ > Rx / || > \ <----||----- OUT > / || C2 > \ > | > | > --- > /// > > No DC current path, right? Correct, and that is what you need. The caps keep the DC for the automute out of the audio circuitry. You need to apply DC to the top of the pot, and take DC off the wiper prior to the cap. If the DC for the auto-mute circuit is completely isolated from the supply for the device, ie, no common ground, no common +, then there's no need to worry about the AC signal being attenuated by finding a path through the DC supply circuit. If it is not isolated, then it becomes a try it and see, with possible difficulty setting a DC level at the top of the pot that works. If you can't isolate, then there is another possible approach. You could apply narrow DC pulses to the top of the pot - too narrow for the audio to be affected. For example, say the pulse was 5 or 10 microseconds long, once every 50 miliseconds. The audio from the speaker should be unaffected even with a common power supply, yet a train of digital pulses would be available at the wiper. A difference in pulse amplitude would indicate that the pot has been moved. Get the pulses at the wiper, and adc to establish a level in a register in a micro. The micro can compare saved_level to current_level and if the delta is equal to or greater than a target, reset the timer. Wouldn't matter if the pot was moved up or down as the micro only cares about the delta between the new reading and the old reading. You still need to be able to find the right connection points to the pot, whatever you try. It's probably worth trying to get schematics for all of the gear you might want to automute. If you can get at least some schematics, it'll save you some work and head scratching. Ed
From: Jon Kirwan on 14 Dec 2009 13:59 On Mon, 14 Dec 2009 12:27:04 -0500, ehsjr <ehsjr(a)nospamverizon.net> wrote: >Jon Kirwan wrote: >> On Sun, 13 Dec 2009 22:47:39 -0500, ehsjr wrote: >> >> >>>Jon Kirwan wrote: >>> >>>><snip> >>>>Do I get the gist so far? >>> >>>Yes, I think you understand it. The hysteresis does what you said, but >>>it was more to make the trigger "window" a little wider, and make the >>>switching crisp and definite. As far as moving the control in either >>>direction, it is solvable as you said. Maybe use a second comparator >>>set up to switch when the control moves in the other direction. As >>>far as muting, use the comparator output(s) to reset the timer, and >>>the timer output to switch the audio output line from the speaker(s) >>>to a resistor or resistors and vice versa. >>> >>>Regarding the existing pot setup, it is often like this, >>>where the signal comes from the preamp: >>> Signal---[cap]---+ >>> | >>> P >>> O<---- signal out to amplifier stage >>> T >>> | >>> Gnd -------------+ >> >> >> Yes. I anticipate this _after_ the first stage's conditioning of the >> input and well before the final power stage. >> >> Suppose that the 'signal out' you mention passes through yet another >> cap before the next stage. If so, isn't this a problem for a DC path? >> >> || C1 >> IN --------||-----, >> || | >> | >> \ >> Rx / || >> \ <----||----- OUT >> / || C2 >> \ >> | >> | >> --- >> /// >> >> No DC current path, right? >> >> In any case, I just opened up my first victim. The pot has 7 points >> of attachment into the PC board. Two of them are twist tabs for the >> main mounting and are themselves grounded. Of the other five, they >> are on 5-hole line tangent at the circumference. One of these is tied >> to the same ground. But the other four 'go somewhere'. >> >> Call the pins A, B, C, D, and E. Pin B is tied to the negative rail >> (ground.) (Since there is a battery system, as well as AC, I can >> verify that it is the most negative rail by using the most negative >> side of the battery pack connection.) >> >> Here are the measurements against ground for two rotation positions: >> >> MIN VOL MAX VOL >> --------------------------- >> A 0.5 ohm 32.3k ohm >> B --- --- >> C 0.5 ohm 32.3k ohm >> D 220 ohm 32.3k ohm >> E 47.7k ohm 32.3k ohm >> >> Obviously, in-circuit and not desoldered. Interestingly, the >> resistance between A and C goes from about 0 ohms to about 64.5k ohms >> going from MIN to MAX volume, respectively. The resistance from C to >> D goes from 220 ohms to 0 ohms going from MIN to MAX, respectively. >> >> That's enough to make this interesting. I need to think more closely >> to be sure, but the pot appears to not be a single resistor track and >> wiper, at first blush. >> >> I think I need to assume every other system will be just as messy. >> Then, at least, the only way is down -- easier -- from there. >> >> >>>>Another issue is what mutes the output. If I actively mute, that act >>>>itself will affect what those same nodes do for the comparator inputs >>>>(filtered and unfiltered) since those nodes must be involved in the >>>>muting, itself. That presents a possible problem. What I may like to >>>>do is separate things so that I isolate the pot and 'copy' its value >>>>to the prior nodes being controlled. Well, that gives me some thought >>>>lines to move along. >>> >>>It should't affect the comparators if it occurs between the final >>>amplifier and the speaker(s). >> >> >> I have a hard time imagining a pot right at the final stage, because >> of the power (few watts, at least) involved. But you might be talking >> about something else I said. >> >> >>>>Possible variations are discrete circuits, IC circuits, and a host of >>>>topologies to ferret out and design around. Maybe the best way to >>>>start is to just start. I'll open up one of the devices and see what >>>>I see there. >>> >>>Good luck! >> >> >> Thanks. Looks like I'm going to need it. Blasted thing. >> >> Jon > >Hi Jon, > >Usually the pot is early in the audio chain, between the >preamp and the power amp stage, something like this: > > input===>preamp===>pot===ground > | > +===>power amp======>speaker > > > >Regarding the following: > > || C1 > > IN --------||-----, > > || | > > | > > \ > > Rx / || > > \ <----||----- OUT > > / || C2 > > \ > > | > > | > > --- > > /// > > > > No DC current path, right? > >Correct, and that is what you need. The caps keep the DC for >the automute out of the audio circuitry. You need to apply DC to >the top of the pot, and take DC off the wiper prior to the cap. yes. I had drawn that modification in a schematic I was going to post and then just removed it because I figured calling attention to it would be enough and I hoped you'd say what I see you saying above. Because it makes complete sense to me (and I was able to figure it out on my own, which is a good thing.) >If the DC for the auto-mute circuit is completely isolated from >the supply for the device, ie, no common ground, no common +, >then there's no need to worry about the AC signal being attenuated >by finding a path through the DC supply circuit. If it is not >isolated, then it becomes a try it and see, with possible >difficulty setting a DC level at the top of the pot that works. Got it. >If you can't isolate, then there is another possible approach. >You could apply narrow DC pulses to the top of the pot - too >narrow for the audio to be affected. For example, say the pulse >was 5 or 10 microseconds long, once every 50 miliseconds. >The audio from the speaker should be unaffected even with a common >power supply, yet a train of digital pulses would be available at >the wiper. A difference in pulse amplitude would indicate that the >pot has been moved. Get the pulses at the wiper, and adc to >establish a level in a register in a micro. The micro can compare >saved_level to current_level and if the delta is equal to or greater >than a target, reset the timer. Wouldn't matter if the pot was >moved up or down as the micro only cares about the delta between >the new reading and the old reading. Understood. That I can do, as well. >You still need to be able to find the right connection points >to the pot, whatever you try. It's probably worth trying to get >schematics for all of the gear you might want to automute. >If you can get at least some schematics, it'll save you some >work and head scratching. Yeah. So there is the pain. Finding that damned schematics for each case. I had early posted the "wish" that this would be applied right at the speaker itself and drew its power from speaker drive power itself. The pair of speaker wires is pretty much universal. Of course, that's a whole other bag of worms. But after looking at this single unit, I'm wondering if it might be worth thinking a little more about. Or just build my own amplifier system, for gosh sake! Then I _know_ what I'm doing and can make it work properly without all the hassle. Of course, I'll need a 'pick-off' point for the existing boxes and devices. Which _could_ be the speakers, though that isn't the usual point -- if I conditioned that before applying it to the amplifier chain. Now why can't manufacturers just realize that an auto-mute function would be handy! I'd buy that. Okay. That seems like the right direction even though it adds an external box that makes this more complex for her and us and takes up more space and adds yet another 'wire system' to trip over or break when she drags things around. Screw the auto-mute built into the boxes. I'll just work on the amplifier design (or select an easily modifiable system that includes case and power.) Jon
From: ehsjr on 14 Dec 2009 22:50 Jon Kirwan wrote: > On Mon, 14 Dec 2009 12:27:04 -0500, ehsjr <ehsjr(a)nospamverizon.net> > wrote: > > >>Jon Kirwan wrote: >> >>>On Sun, 13 Dec 2009 22:47:39 -0500, ehsjr wrote: >>> >>> >>> >>>>Jon Kirwan wrote: >>>> >>>> >>>>><snip> >>>>>Do I get the gist so far? >>>> >>>>Yes, I think you understand it. The hysteresis does what you said, but >>>>it was more to make the trigger "window" a little wider, and make the >>>>switching crisp and definite. As far as moving the control in either >>>>direction, it is solvable as you said. Maybe use a second comparator >>>>set up to switch when the control moves in the other direction. As >>>>far as muting, use the comparator output(s) to reset the timer, and >>>>the timer output to switch the audio output line from the speaker(s) >>>>to a resistor or resistors and vice versa. >>>> >>>>Regarding the existing pot setup, it is often like this, >>>>where the signal comes from the preamp: >>>>Signal---[cap]---+ >>>> | >>>> P >>>> O<---- signal out to amplifier stage >>>> T >>>> | >>>>Gnd -------------+ >>> >>> >>>Yes. I anticipate this _after_ the first stage's conditioning of the >>>input and well before the final power stage. >>> >>>Suppose that the 'signal out' you mention passes through yet another >>>cap before the next stage. If so, isn't this a problem for a DC path? >>> >>> || C1 >>> IN --------||-----, >>> || | >>> | >>> \ >>> Rx / || >>> \ <----||----- OUT >>> / || C2 >>> \ >>> | >>> | >>> --- >>> /// >>> >>>No DC current path, right? >>> >>>In any case, I just opened up my first victim. The pot has 7 points >>>of attachment into the PC board. Two of them are twist tabs for the >>>main mounting and are themselves grounded. Of the other five, they >>>are on 5-hole line tangent at the circumference. One of these is tied >>>to the same ground. But the other four 'go somewhere'. >>> >>>Call the pins A, B, C, D, and E. Pin B is tied to the negative rail >>>(ground.) (Since there is a battery system, as well as AC, I can >>>verify that it is the most negative rail by using the most negative >>>side of the battery pack connection.) >>> >>>Here are the measurements against ground for two rotation positions: >>> >>> MIN VOL MAX VOL >>>--------------------------- >>>A 0.5 ohm 32.3k ohm >>>B --- --- >>>C 0.5 ohm 32.3k ohm >>>D 220 ohm 32.3k ohm >>>E 47.7k ohm 32.3k ohm >>> >>>Obviously, in-circuit and not desoldered. Interestingly, the >>>resistance between A and C goes from about 0 ohms to about 64.5k ohms >>>going from MIN to MAX volume, respectively. The resistance from C to >>>D goes from 220 ohms to 0 ohms going from MIN to MAX, respectively. >>> >>>That's enough to make this interesting. I need to think more closely >>>to be sure, but the pot appears to not be a single resistor track and >>>wiper, at first blush. >>> >>>I think I need to assume every other system will be just as messy. >>>Then, at least, the only way is down -- easier -- from there. >>> >>> >>> >>>>>Another issue is what mutes the output. If I actively mute, that act >>>>>itself will affect what those same nodes do for the comparator inputs >>>>>(filtered and unfiltered) since those nodes must be involved in the >>>>>muting, itself. That presents a possible problem. What I may like to >>>>>do is separate things so that I isolate the pot and 'copy' its value >>>>>to the prior nodes being controlled. Well, that gives me some thought >>>>>lines to move along. >>>> >>>>It should't affect the comparators if it occurs between the final >>>>amplifier and the speaker(s). >>> >>> >>>I have a hard time imagining a pot right at the final stage, because >>>of the power (few watts, at least) involved. But you might be talking >>>about something else I said. >>> >>> >>> >>>>>Possible variations are discrete circuits, IC circuits, and a host of >>>>>topologies to ferret out and design around. Maybe the best way to >>>>>start is to just start. I'll open up one of the devices and see what >>>>>I see there. >>>> >>>>Good luck! >>> >>> >>>Thanks. Looks like I'm going to need it. Blasted thing. >>> >>>Jon >> >>Hi Jon, >> >>Usually the pot is early in the audio chain, between the >>preamp and the power amp stage, something like this: >> >> input===>preamp===>pot===ground >> | >> +===>power amp======>speaker >> >> >> >>Regarding the following: >> >>> || C1 >>> IN --------||-----, >>> || | >>> | >>> \ >>> Rx / || >>> \ <----||----- OUT >>> / || C2 >>> \ >>> | >>> | >>> --- >>> /// >>> >>>No DC current path, right? >> >>Correct, and that is what you need. The caps keep the DC for >>the automute out of the audio circuitry. You need to apply DC to >>the top of the pot, and take DC off the wiper prior to the cap. > > > yes. I had drawn that modification in a schematic I was going to post > and then just removed it because I figured calling attention to it > would be enough and I hoped you'd say what I see you saying above. > Because it makes complete sense to me (and I was able to figure it out > on my own, which is a good thing.) > > >>If the DC for the auto-mute circuit is completely isolated from >>the supply for the device, ie, no common ground, no common +, >>then there's no need to worry about the AC signal being attenuated >>by finding a path through the DC supply circuit. If it is not >>isolated, then it becomes a try it and see, with possible >>difficulty setting a DC level at the top of the pot that works. > > > Got it. > > >>If you can't isolate, then there is another possible approach. >>You could apply narrow DC pulses to the top of the pot - too >>narrow for the audio to be affected. For example, say the pulse >>was 5 or 10 microseconds long, once every 50 miliseconds. >>The audio from the speaker should be unaffected even with a common >>power supply, yet a train of digital pulses would be available at >>the wiper. A difference in pulse amplitude would indicate that the >>pot has been moved. Get the pulses at the wiper, and adc to >>establish a level in a register in a micro. The micro can compare >>saved_level to current_level and if the delta is equal to or greater >>than a target, reset the timer. Wouldn't matter if the pot was >>moved up or down as the micro only cares about the delta between >>the new reading and the old reading. > > > Understood. That I can do, as well. > > >>You still need to be able to find the right connection points >>to the pot, whatever you try. It's probably worth trying to get >>schematics for all of the gear you might want to automute. >>If you can get at least some schematics, it'll save you some >>work and head scratching. > > > Yeah. So there is the pain. Finding that damned schematics for each > case. > > I had early posted the "wish" that this would be applied right at the > speaker itself and drew its power from speaker drive power itself. The > pair of speaker wires is pretty much universal. Of course, that's a > whole other bag of worms. But after looking at this single unit, I'm > wondering if it might be worth thinking a little more about. > > Or just build my own amplifier system, for gosh sake! Then I _know_ > what I'm doing and can make it work properly without all the hassle. > Of course, I'll need a 'pick-off' point for the existing boxes and > devices. Which _could_ be the speakers, though that isn't the usual > point -- if I conditioned that before applying it to the amplifier > chain. > > Now why can't manufacturers just realize that an auto-mute function > would be handy! I'd buy that. > > Okay. That seems like the right direction even though it adds an > external box that makes this more complex for her and us and takes up > more space and adds yet another 'wire system' to trip over or break > when she drags things around. Screw the auto-mute built into the > boxes. I'll just work on the amplifier design (or select an easily > modifiable system that includes case and power.) > > Jon Well, you could do it at the existing speaker(s) with an active rectifier to develop a DC level, but I can't figure out how to make it reliable, because audio level constantly changes without moving the volume control. So your idea of building an amp with automuting sounds best. One other possibility, which depends on your life situation knowledge. A ten minute (or whatever) timer mutes the speaker AND turns on a mic & amp VOX circuit. The mic circuit would be off during the 10 minute period so that it won't detect sound from the equipment when it is not muted. If that circuit detects noise from her normal activity, it resets the timer and un-mutes. The noise from her normal activity is the key - if her activity to go to the equipment & turn the volume control can be detected that approach might work. Ed
From: Jon Kirwan on 14 Dec 2009 23:33 On Mon, 14 Dec 2009 22:50:23 -0500, ehsjr <ehsjr(a)nospamverizon.net> wrote: ><snip> >Well, you could do it at the existing speaker(s) with an active >rectifier to develop a DC level, but I can't figure out how to >make it reliable, because audio level constantly changes >without moving the volume control. So your idea of building >an amp with automuting sounds best. There is plenty of power when the volume is UP, which is when I most need muting after a delay. Other times it would work if it could stand out of the way and not mute, I suppose. Best is to have a consistent muting behavior, though. Higher power outputs (and we have some that are blasting away at 20-30 watts, maybe) mean fairly high drive voltages and passing and blocking those may not be straight-forward. In any case, deriving power for the circuit from the speaker output power only makes the whole thing seem even more outside my skills. I think most of the stuff I have either has a headphone jack or else a line out (or both.) The line out wouldn't disable output, while the headphone jack usually does. Their signal levels and drive impedances are different, so each would need a slightly different 1st stage -- but I could arrange an either-or circuit for that (after I figure out what the signals are like.) The rest isn't hard and I don't need high fidelity or high power outputs. This doesn't have to be a 30-watt plastic tiger. A quasi-complimentary output and perhaps a diff-amp pair before it seems all that is necessary. I _do_ need to spend some time figuring out what phone jack and line outputs look like though. I am ignorant, there. >One other possibility, which depends on your life situation >knowledge. A ten minute (or whatever) timer mutes the speaker >AND turns on a mic & amp VOX circuit. The mic circuit would be >off during the 10 minute period so that it won't detect sound >from the equipment when it is not muted. If that circuit detects >noise from her normal activity, it resets the timer and un-mutes. >The noise from her normal activity is the key - if her activity >to go to the equipment & turn the volume control can be detected >that approach might work. You are making me like the homebrew amplifier even more. ;) Jon
From: JosephKK on 19 Dec 2009 14:17
On Fri, 11 Dec 2009 17:33:16 -0800, Jon Kirwan <jonk(a)infinitefactors.org> wrote: >To start off, I'm not looking for a specific design, though of course >I will be very happy for any such attempts. I'd like some thoughts >about approaches or problems I may need to consider. I'd be happy to >then expose some design I come up with, to criticism. > >I need an auto-mute circuit that I can use to retrofit devices that >provide an amplified audio output to a speaker or speaker pair. These >include television sets which use UP/DOWN buttons to set volume all >the way to resistor-based knobs and wheels that set volume. > >I could consider not "getting everything" and instead just focusing >only on those devices which use a resistor to control the volume, >interceding at that point (using the existing control but adding a >circuit around it.) In that case, the circuit would need to behave >the same regardless of which resistive 'end' was used to set the >highest volume. I'd like to handle TV sets that use UP/DOWN buttons, >too. But even _some_ solutions are better than none. > >By 'retrofit' I mean that I cannot add new control systems to existing >ones by drilling holes and making the operation more complex to handle >-- the operation must be fully automatic and set by me _before_ I open >up the units and insert the circuit, without having to create any >external access holes or buttons, etc. > >My daughter has grand mal seizures that my wife and I need to hear the >beginnings of. My daughter loves to turn on stereo systems and music >boxes, quite loud at times. She enjoys listening and often has her >computer software playing something loud while having a CD player >playing something else in the same room, while still something else is >playing on a CD player in the next room, as well. We don't want to >take that away from her, but it also makes for a noisy environment >which can easily mask our ability to detect a seizure as early as we'd >like to. The results of our missing the early sounds of a seizure >event could potentially lead to broken arms, or even death in an >extreme case. So this can have very important consequences. > >We've used timers on the power plugs. But besides the fact that she >moves things around from place to place if it "doesn't work" from her >point of view, using a timer greatly complicates our own life. She >needs to have the ability to initiate the operation by using controls >that already exist on the device. (She is 25 years old, but operates >much like a 4 year old. She can learn some things, like how to turn >the volume control knob, but using timer boxes greatly complicates >operation and thus greatly complicates both her and our lives.) > >What I need is something that doesn't increase the complexity of her >use of the device. She simply needs to learn to "adjust the volume" >as she always does to cause the mute operation to cease, instantly. >But that action should initiate the start of a new timing cycle. The >auto-mute effect needs to take place after about 10 minutes of use, >but I'd like to be able to set that range from perhaps 1 minute to 15 >minutes. That said, to be completely honest about it, I could live >with a fixed 10-minute delay. > >The power source is an issue. These devices I'd modify _do_, of >course, have internal power supplies and I could scarf around to find >something to attach to, of course. How the ground will relate to the >speakers, I don't know. It may depend on the device. The speaker >outputs may even be galvanically isolated. Best would be that energy >is derived from the sound system's own delivered power to the >speakers, so that it's 'universal' in that regard. This would save me >from replacing batteries or having to make custom designs for each and >every situation's internal supply modifications. (While the voltage >is building up in such a case, though, I'd like the unpowered circuit >situation to be 'unmuted.') But battery powered, if necessary, is >acceptable if I don't have to replace them more often than once every >few months and so long as I'm able to fit the battery system inside >(in some cases, that will be 'hard'.) > >What would work best for her is that if she 'fiddles' with the volume >control, the mute operation ceases and the timer starts. > >This needs to work on CD and karaoke players, stereo and mono >amplifiers, TVs, etc. Almost all are wall-plug powered. Not all, >though. Some use multiple D-cells ('boom boxes') or allow an >'either-or' operation, using batteries if unplugged from the wall. > >I've only just begun to think about this and my own limitations in >experience are suddenly in evidence to me. My first thought would >only work on the resistive type controls, would use a micro to monitor >the value (ADC) and then control a digital POT I select. It would >need power but I could use an MSP430 to mitigate that problem, using a >small CR2025 or CR2032 which would last quite a while. (The timing >requirement of minutes, alone, almost forces me to think in terms of a >micro, though I can think of a few analog circuits using a cap and >mosfet that would handle such times.) I would probably need custom >programming, a tweak for the input gain perhaps, and perhaps a >different digital POT for each unit I modified. But at least I can >see how to handle that. > >Thoughts and criticisms meant constructively are appreciated. > >Jon For bog simple muting and low energy consumption consider latching relays: maybe like this of even in a to99 can. http://www.futurlec.com/Datasheet/Relays/HFD2.pdf And whenever possible, switch at signal levels. |