retrofitting an auto-mute volume control?
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From: Jon Kirwan on 11 Dec 2009 20:33 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
From: osr on 11 Dec 2009 22:45 THAT Corporation makes nice AGC/MUTE chips with compression/expansion/ log detection. www.thatcorp.com Steve
From: Vladimir Vassilevsky on 11 Dec 2009 23:20 Jon Kirwan wrote: > To start off, I'm not looking for a specific design, though of course > I will be very happy for any such attempts. This is not a technical problem. It can't be solved by any technical means. VLV
From: Jon Kirwan on 12 Dec 2009 00:15 On Fri, 11 Dec 2009 22:20:42 -0600, Vladimir Vassilevsky <nospam(a)nowhere.com> wrote: >Jon Kirwan wrote: >> To start off, I'm not looking for a specific design, though of course >> I will be very happy for any such attempts. > >This is not a technical problem. It can't be solved by any technical means. I'm not sure what problem _you_ are talking about. The question _I_ asked can be addressed from a technical perspective, at least in piecewise fashion. If you are referring to the larger problem of life itself and the issues we as a family face, I wasn't asking for a solution to that. Jon
From: Jon Kirwan on 12 Dec 2009 00:15
On Fri, 11 Dec 2009 19:45:02 -0800 (PST), osr(a)uakron.edu wrote: >THAT Corporation makes nice AGC/MUTE chips with compression/expansion/ >log detection. > >www.thatcorp.com A little too 'jazzy' a web page, for one thing. I'd be fine just building a micro to handle the ADC-to-digipot thing, so if the offering is more expensive or has a longer learning curve for someone used to doing embedded stuff, I may pass. At least, I'd know I'd get exactly what I needed, doing it by hand. Anything there you wanted to draw my attention towards? Jon |