The Siren Board

i have pondered this question for a while, what happens when a whelen or any kind of FS siren is activated i know it uses dtmf but how does that signal activates a warning tone

whelen4004tech wrote:i have pondered this question for a while, what happens when a whelen or any kind of FS siren is activated i know it uses dtmf but how does that signal activates a warning tone

Well basically that DTMF tone is received and recognized by the receiver/decoder and then that activates the control (sound card circuits and other circuits?) and starts up the drivers in the signal required by the DTMF sequence.

Hopefully somebody can take this a bit more in depth.

Thunderboltlover wrote:

whelen4004tech wrote:i have pondered this question for a while, what happens when a whelen or any kind of FS siren is activated i know it uses dtmf but how does that signal activates a warning tone

Well basically that DTMF tone is received and recognized by the receiver/decoder and then that activates the control (sound card circuits and other circuits?) and starts up the drivers in the signal required by the DTMF sequence.

Hopefully somebody can take this a bit more in depth.

i can't seem to find patents on them either, but i guess that whelens and some federal signal controllers might use digital signal processors (DSP)

The two tone, DTMF, or digital signal gets received by the radio transceiver, and the logic in the controller wakes up and decides what to do with the request, whether that be to activate the requested siren signal, run a test sequence, rotate the siren, play a voice message, broadcast live voice, cancel a signal, etc.

They are always listening as long as they have power, working radios and intact antennas. It also helps greatly if there's no radio interference.

Usually the two tone sequence decoders are one way, the base can only command the sirens. Fire voice pagers like the Minitors are also activated this way.

The DTMF speed dial that Whelen uses, the FSK signal used by American Signal Compualert, and the MSK signal used by Federal's controllers are all usually two way where the siren units can/do report back to the base console if it is OK or not:

"siren5 to base, I am here and all is working" or
"siren5 to base, help! my batteries are DEAD!" (for instance)

There's lots of examples of two tone and DTMF activations on Youtube.

ASC's Compualert sounds like a nice warbling noise.
The Federal Commander protocol sounds like a raspy squawk, much like packet radio if any of you are familiar with that at all.

One of these days I need to capture nice clean examples of all of these live off the air here.

Whelen, Federal, and ASC all have manuals describing their *RTUs in great detail on their respective sites if you need more detail.

*RTU remote terminal unit, i.e. the controller cabinet on the post at each siren station.

-b-