BSII as "Dead Air" detector?

Vern Graner

Before I "reinvent the wheel" I wanted to know if anyone had created a "dead air" detector using the Basic Stamp?

For those of you not aware of this term, "dead air" refers to what happens when a radio station stops sending audio. For example if the DJ goes off to the restroom and the song finishes and there's no one there to kick off the commercials, talk or spin another disk, you get "dead air" which is anathama to radio stations.

I have a request to create a device that would monitor the audio output from the station and then perform a digital task if it detects dead air (i.e. send an email, or auto-trigger a CDplayer to play some music etc.). I was envisioning using a full-wave bridge rectifier to convert headphone audio output AC to DC, then using a small cap to smooth it out. Add a zener diode to clamp the voltage level to a reasonable level, then hooking that to a pin on the stamp and watching for the input to go to "zero" (i.e. dead air).

Anyone done this already, or does anyone have any comments on my design?

Vern

Paul Roy

I haven't tried it, but I think the Basic stamp could do it though by monitoring the voltage of the signal and if it stays at zero for so long then trip a relay to trip the alarm.

I know the station I work for uses the Gentner Silence sensor Part Number 910074001.

That's my thought.

Paul

Newzed

Why not use an ADC to monitor the audio voltage.· When the ADC digital output drops below a certain level - there is your "alarm".

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Sid Weaver
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Worapoht

Another idea, using external comparator (such as LM311) and tied output to Stamp.
write code as timer.. and use comparator input as timer reset.
if no any signal on time, alarm it..

abstract circuit, set sound sensitivity level by potentiometer at invert pin(+)
and audio input with RC lowpass filter to non-invert pin(-) and output to Stamp with 10k resistor pullup.. then apply some code..



Post Edited (Worapoht) : 10/29/2004 3:21:30 PM GMT

Jon Williams

I know this to be possible because I wrote the code for such a device (before joining Parallax) that gets used by some radio stations (the circuit was designed by somone else). I will see if I can track down the code to figure out which compoent was actually used to detect "dead air."

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Jon Williams
Applications Engineer, Parallax
Dallas Office

Chris Savage

I agree with Worapoht's idea, which I have used before to detect silence and shut down a power-amp after a specified period of time.· The input was fed into comparator through a half wave rectifier using a cap as a filter.· Then you can adjust the sesitivity as Worapoht said, using a pot on the other input.· Center pin to the input, one outer pin to ground, one to Vcc.

Another idea uses a chip which I myself use for VU Meters, but which a member of the Yahoo Group (I don't know if he's on this forum) used to detect the end of a song in his Home-Brew Jukebox.· As I recall he used an LM3914 Dot/Bar Display Driver chip.· This chip will output a low on 10 different outputs indicating the level of music.· I believe he tested the lowest pin for low output, and if not low for a specified time, the song was over.

You can also half-wave rectify the signal and buffer it with a cap for better response.· Both ideas work best with Line Level audio (1V Peak to Peak).



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Chris Savage

Knight Designs
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P.O. Box 97
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