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Old 28th June 2006, 07:11 AM   #1
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Join Date: May 2006
Default Read "volume" level and display remotely

OK, I'm a "Radio Shack" electrician, and barely that. But I know enough to put together things like IR extenders where I took an IR receiver and aimplified it a tiny amount out to several IR emmitters so that I can control my stereo components with the remote and with the solid wood doors closed. Just the receiver sitting on top of the TV and the emitters running and stuck to the inside of the cabinet doors.

There are, however, times when you'd really like to know information that is only displayed on one of those units behind the door. Most often, it's the amplifier volume level (yes, I know you could just go up/down a bit and see where you're at, but these new amps use logarithmic scales for their volume sweeps and it makes it tricky and annoying (but appropriate, as that's how our hearing also works)).

So, I'd like to be able to hook something up to the amp, I was first think the phono out (as I never use it, and certainly not with the cabinet door closed), but interrupting that circuit turns the speakers off. Then I was thinking about a line level out or one of the set of speaker outs, the first being preferred because of much lower voltage levels.

HEre, however, is where my electronics knowledge ends. Anyone know if a circuit design that could be hooked up to a numeric LED (or "LED tree", etc...) to show what the current volume level was, relative to the max/min? Thanks for any ideas,

Terry Parker
terryparker@myself.com
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Old 28th June 2006, 07:37 AM   #2
AndrewT is offline AndrewT  Scotland
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Location: Scottish Borders
Hi,
those LED bargraph displays are available as log and lin and can be set for dot or bar mode.
They can be cascaded, but I suspect the accuracy of the log version may be suspect when used this way. Maybe accuracy is not an issue.

Hopefully someone will point you to a numerical log scaled output driver.
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Old 5th November 2006, 04:55 AM   #3
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Default Still stuck on this one

I had posted this on another board and someone mentioned a product they'd seen somewhere, but couldn't remember where, that would do just what I was looking for. Anyone know of such a product or can you point me to a design that would work?

It seems to me that you should be able to take one of the line level or pre-outs that isn't being used, amp it up a bit to the voltage level needed to drive an LED tree and voila, I've got some way of seeing where the volume "is" and how much I'm turning it up/down.

My understanding is that standard line level reference is +4dbV or about 1.22 volts. Most of the LED's I have or have seen run around 12 volts (and I haven't found a "tree" or something that'll convert a voltage level into a number, that would take at least some type of ttl chip, I'm assuming).

It's a little problem, but it's an annoying one.
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Old 5th November 2006, 08:24 AM   #4
AndrewT is offline AndrewT  Scotland
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Join Date: Jul 2004
Location: Scottish Borders
Hi,
LM3915 is the log scaled version of the bargraph display.
They are also available in lin and Vu.

A similar chip is available from other manufacturers.
Look up the datasheet for details of circuits and cascading.

A twenty dot display (on each channel) with peak hold (rather than slow decay) is impressive. Much better than the 6 dot on the DCX2496.
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