name this thing.....

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havanashavanas
Posted:
in General Discussion edited January 2014
I'm looking for the name of something but have no luck Googling it.



My old college roommate had one... it looked like it was the seventies.



Basically it was a tiny box which took in an audio single and power from the wall. What it did was vary the voltage/amplitude from the wall in sync with the audio signal being input (either speaker cable or RCA... can't remember).



I hooked my multicolor xMas lights(which circled my ceiling) into it.... suffice to say I never needed to buy drugs at college.... that was good enough... so I want that again.



Does anyone have any kind of name for such a device?

Is it common....does radio shack have them?



Come on ...help me save rave xMas!!!

Comments

  • Reply 1 of 6
    paulpaul Posts: 5,278member
    that would be HOT for our dorm...

    I should take pictures...

    and if this device turns up I will definitely be getting one and posting the results
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  • Reply 2 of 6
    splinemodelsplinemodel Posts: 7,311member
    Ahhhh, analog electronics. I LOVE analog electronics.



    This device is, technically speaking, a DSB modulator. I'd build one for you if I had the time. DSB modulation was used to communicate with early space probes. (Voyager)



    1. 120VAC goes in at 60Hz, an audio signal goes in (0 to 20kHz).



    2. Audio is hit with a big 'ol low pass filter to keep oscillations below, say 5Hz. You want this for several reasons: it allows the multiplier to work well with the 120VAC as the carrier, it keeps light changes to discernable volume changes. A 2nd order butterworth filter should be fine here.



    3. audio signal is normalized. the easiest way to do this is with a voltage divider, but you'll probably want something a little more inteligent. for simplicity, I'd use a potentiometer (knob controlled resistor) followed by a voltage limiter (zener diode bridge) to keep the voltage from -1V to +1V.



    4. build the signal multiplier out of amps and passive elements. cookbook here, but you'll need some beefy amps and passive elements to deal with the currents and high voltages from the 120VAC carrier.



    The output is actually a DSB modulated signal (similar to AM) with a 120V RMS. You could broadcast it if you had a 60Hz antenna, but those take up more space than Rhode Island.
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  • Reply 3 of 6
    curiousuburbcuriousuburb Posts: 3,325member
    pretty sure it would have been sold at Radio Shack. ask them
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  • Reply 4 of 6
    alcimedesalcimedes Posts: 5,486member
    lol, Spline, i hope you realize how far that went over most people's heads.



    although



    http://www.gme.net.au/matv/dsb_modulators.html



    this would help you out.
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  • Reply 5 of 6
    torifiletorifile Posts: 4,024member
    Quote:

    Originally posted by alcimedes

    lol, Spline, i hope you realize how far that went over most people's heads.





    alcimedes, that's Splinemodel's schtick



    -t



    ps - the psychologist is back in the house
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  • Reply 6 of 6
    splinemodelsplinemodel Posts: 7,311member
    Quote:

    Originally posted by alcimedes

    lol, Spline, i hope you realize how far that went over most people's heads.



    although



    http://www.gme.net.au/matv/dsb_modulators.html



    this would help you out.



    Yeah, I got a little carried away there. At the time I was actually solving a problem involving noise in an AM receiver. Much of the math between AM and DSB is similar.



    As for the link, I don't think it would work. As for DSB, it is pretty dead, at least in this country. Broadcast TV actually uses SSB (single side band, rather than dual side band. . . too much to explain), but that's because it has been around for so long. With digital, a lot of the noise problems as well as the bandwidth problems of analog can be overcome. There are costs involved, namely transmission power and reciever/transmitter complexity, but it's worth the cost in most cases, especially these days when you can get a PPC 750 board or whatnot and do an enormous amount of calculations on less than 5W.



    Anyway, for a little survey lesson, DSB never got much use because it's hard to make a DSB receiver. An AM receiver is easy to make. . . really easy. It was used on probes because it has a more efficient transmission characteristic than AM (or pretty much anything else).



    But the lights don't need to demodulate, so the carrier phase isn't important.
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