This project interfaces an emergency broadcast radio to my home's paging network. If there is a tornado warning, it will connect the radio to my PBX and broadcast the audio all over the house, and out to our cellphones, etc. This works GREAT and it has been in use for 11 years now. The problem is that a few times a year, it mysteriously trips and just clicks on and off for around 20 minutes. This is very annoying, especially if it happens at 3 am.
So here's the theory. The radio receiver headphone jack is connected to J2. I used an LM358 as a detector, and a time delay. When audio is detected, U2 is energized and the audio is coupled to a 600 ohm isolation transformer connected to the PBX paging system at J3. It works great.
On the rare occasions I get this false triggering, if I unplug the audio from J2 it stops. However, there is nothing happening on the radio when the false trigger occurs that I can detect. The radio is squelched. I thought that T1, the 600:600 transformer would sufficiently isolate the radio from the LM358. It also provides the necessary 600 ohm load that triggers the phone system. R10 was added as an afterthought to lower the volume, I know it's ugly.
Any help on how I can improve this and eliminate the ghost pages? Thanks for looking.
So here's the theory. The radio receiver headphone jack is connected to J2. I used an LM358 as a detector, and a time delay. When audio is detected, U2 is energized and the audio is coupled to a 600 ohm isolation transformer connected to the PBX paging system at J3. It works great.
On the rare occasions I get this false triggering, if I unplug the audio from J2 it stops. However, there is nothing happening on the radio when the false trigger occurs that I can detect. The radio is squelched. I thought that T1, the 600:600 transformer would sufficiently isolate the radio from the LM358. It also provides the necessary 600 ohm load that triggers the phone system. R10 was added as an afterthought to lower the volume, I know it's ugly.
Any help on how I can improve this and eliminate the ghost pages? Thanks for looking.
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