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loumeinhart

need help electronic/relay problem phone horn

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I need to ring a phone that activates a loud ass horn. Phone has no audio ports. I'd be tapping into the 2 wires that connect from phone circuit board to the phone ring speaker.

Inside the handset, the 2 wires show .035-.045 VAC (probed with multimeter while the phone "rings") and connect to an 8 Ohm 2W speaker inside the phone. This 8 Ohm 2W speaker needs to be replaced with a very loud horn or buzzer.

-I purchased a generic 12VDC piezo horn. Need to feed it 12VDC when phone rings. That's all. 

I'm stumped. Low signal relay? Some type of inline amp? I can solder a bit, and have only  a very basic understanding of this stuff. 

Do I look for a low signal relay? like .03VAC to 12VDC?

Thank you

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On 12/19/2021 at 8:05 AM, loumeinhart said:

I need to ring a phone that activates a loud ass horn.

OK.  First you need something like a 'scope to see the signal.  Remove the piezo then look at the ring signal with the 'scope.  You'll see a square wave with some amplitude and frequency.

If that amplitude is over .6 volts you're in luck.  You can drive the base of an NPN transistor with that, and use the transistor to drive a much larger speaker at the same frequency.

If you need a different frequency, you'll need a filter to remove the AC frequency after the transistor amplifier, then use that DC signal to turn on a louder horn.

If it's below .6 volts you will need to get fancier with a bias network so that the transistor can amplify the weaker signal.  That's still doable but you'd need to know what the waveform was first.

(To get an oscilloscope find a friend who works with electronics.  They are common items.)

Quote

(someone else said) that can't be right. 2W at 0.035V means 57A of current.

The speaker is rated 2W.  Doesn't mean it's always outputting 2W.

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my first question would be is this a landline or cell phone?  pots lines make 24vdc or thereabouts when they ring, should be fairly easy to step down with something like a small resistor but it's been a while and i'd have to look it up.  if it's a cell, then i have no idea at all.

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