Silence Detector

[Albert H]

It's happened to all of us - CD skips while you're not in the studio, someone fails to load sufficient programmes into the playout computer, DJ falls asleep in the studio..... They all lead to the same result - silence!
There are all sorts of ways of detecting silence, but this was about the most reliable way I could come up with with a very limited supply of components and at short notice after a friend's student station had gone silent for a couple of hours overnight:

silence_detect_V2-1.jpg

The logic is simple, and the analogue timing might be (slightly) inaccurate (depending on the tolerance of the 220µ timing capacitor), but it gets the job done. The relay output can be used to sound an alarm (or set off a small charge under the DJ's chair!), or trigger the sprinklers (but that's really evil!).....

With a bit more effort, I could have derived seconds from a crystal divided down and counted them to give exact timing, resetting the counter when audio is present. This would be the way I'd go if I was going to write a PIC for a silence detector..... I might try that way in the future - I'll put up the code on here if it would be useful to anyone.

The switches can reset (pushbutton) or disable (toggle switch), and the LEDs indicate what it's doing. I used 5mm LEDs across the front panel - blue for power present, red for disabled, green for enabled (could be a bicolour type if you have one available), amber that blinks with audio and comes on solidly on silence, and finally a 15mm hyper red job for the alarm. I used internal jumpers to set the way it works - the silence period allowed and whether it automatically resets or not.

[rigmo]

interested to finish and check it ?

[Albert H]

That's quite neat. It occurred to me to use a ULN2004 IC (full of Darlington pairs) to drive the LEDs and the relay, to get rid of all the discrete transistors.

It might also be worth making the sensing threshold adjustable to cater for various line levels, or make the input stage have variable gain. I'd also be inclined to bring the adjustment points out to the same edge of the board as the LEDs so that these could be adjusted through small tweaking holes in the front panel. The audio, power and relay output terminals should come out of the opposite edge of the board to the LEDs so that they would easily go to rear panel sockets.

I started working on the PIC version of the silence detector, and it looks like I'll be able to put it into a 16F628 with ease! The permitted silence period would be selected with DIP switches (in binary), and the audio detection might have to still be done in hardware, but I'm trying to see if I can do that in the PIC too.

[radium98]

That what i was looking for , and just to hobbie fan needs , i did one before , adewind who made me the design , i will search for picture but failed to work , i saw one digital also . but my need is like this but if the main audio fail it turn to audio b , if audio b fail can trigger an extra relay , and if main audio A is back it return back , and threshold and foldback time is set by a pot

[radium98]

good morning . promised to put what i have and what i did but failed , so i wait what you will do guys ...
two pictures is the one i did with ne555 and 4066 . the other one is picture from the internet about a digital one , named mp3 guard with can trigger an mp3 player etc ....with some random jingles .

[Albert H]

I've thrown mine together on stripboard, and tried it out. It works reasonably well, but the delay can be a bit variable (because of the leakage of the timing capacitor). I'm going to (slightly) re-design it, with a crystal-derived clock and a presettable counter which can be accurately set in seconds.

Watch this space!

[RF-Head]

I made mine version with a LM3915 (ledbar ic) and used the 8 led to feed a optocoupler with a capacitor on the input as time delay and the output of the optocoupler to a relay
Later version used a DG211 as a audio switch I(like 4066)

[rigmo]

[3metrejim]

Seems a little complicated. I'd use a 4060 with RC oscillator that keeps being reset by the audio detection instead of the mono-stables. When the count reaches a certain output (some multiple of 2) a transistor disables further reset pulses and the alarm is activated. A similar circuit has been used for years to keep extractor fans running after their trigger signal has been removed.

[3metrejim]

I hope that this isn't another 'bob-in-eye' post. Walsh encoder from an amateur radio site, a modulator re-drawn from vrtp, and now something with more than a passing resemblance to this...

http://www.blitzfamily.eclipse.co.uk/pa ... p/art1.htm

(go down the page to the high res circuit, there are definite signs of plagiarism - now I am sad )

[Albert H]

Nope - it's been on a certain German site I used to frequent since 2011 or so, but got updated recently to add the front panel. A company in Hungary are making a version of it using a crystal-derived seconds timer, using my PCB sketches that were uploaded too. As I recall, there are board layouts up on OSHpark. This version was knocked together because I was working in a school and had limited component access at the time (I had to use what was available). There are other iterations of this circuit around (including one made by Alice and sold through Canford) and it uses almost exactly the same audio detector (which is the best possible solution because it can be calibrated to ignore low level noise frequently found in cheap studio set-ups). I've got the very original prototype here on a chunk of Veroboard...... The original has 10-turn presets for the level detection settings!

[radium98]

what is new here ? rigmo. Anyone is planning to make it on pcb ?