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I am to develop a system that senses an alert from a software running on the computer and triggered the MCU

In more detail, there is a program that is running on the computer that alerts the person with a really loud sound(like a siren), so what happens is this person could be away sometimes. so I need to find out when that alarm is going off and signal my MCU to do "it's thing"

The problem that I am having is how to make that triggering; 1- Reliable 2- Secure so it won't go off by any other noise. I need to make it as easy as possible, do you think i have to write a program to read the sound card and triggers the MCU when the alarm went off or can I use a microphone, and analog sig. Find the Freq of the 'siren', and signal the MCU when it heard a sound in that freq from the computer?

Any help will be much appreciated

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  • \$\begingroup\$ What software are you using? \$\endgroup\$
    – HL-SDK
    Commented Sep 16, 2013 at 20:53
  • \$\begingroup\$ I can't make any changes to the software, it's a software that the security personnel use 24/7 so I don't want to interfere with the software, I am trying to acquire signal (in this case loud sound) and use it as my input \$\endgroup\$
    – Caspian
    Commented Sep 16, 2013 at 20:54
  • \$\begingroup\$ I was thinking about that, but there are other sounds, is it possible to limit the inout, maybe a pass filter for something in that Freq? at least limit them some how \$\endgroup\$
    – Caspian
    Commented Sep 16, 2013 at 21:05
  • \$\begingroup\$ A series resistor connecting the speaker output to a microcontroller input would be the lowest-cost lowest-effort solution. On the micro you could then detect presence/absence of a signal. If you can turn all other computer sounds off except the alarm, you will not get false positives (except for plugging/unplugging) \$\endgroup\$
    – HL-SDK
    Commented Sep 16, 2013 at 21:06
  • \$\begingroup\$ Yes, you should make a bandpass filter if you need selectivity but this is not reliable enough in my opinion. Depends on the alarm. \$\endgroup\$
    – HL-SDK
    Commented Sep 16, 2013 at 21:07

1 Answer 1

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There s a simple solution. The duration of the alarm tone may be the trigger you need for arduino. Match electrically arduino input with speaker output. A simple RC circuit may do. Add another capacitor, to integrate the sound voltage, from gnd to the input pin. This will at least soften the audio waveform. In software, make a permissive routine, that for certain amount of time must receive certain amount of pulses or analog readings. This model will ignore clicks and sudden noises.

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