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FM Transmitter Question...

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TMKChef19

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I have always wondered if one could do this:
If one has a transmitter that plugs into the headphone jack on an iPod or mp3 player but wanted to turn it into a broadcaster could they just simply strip the headphone cord and attach a microphone to it?
 
No, not directly at least, microphone's don't output any signal without power going to them. Typical microphones are electret mics, AKA piezo microphones. They require 2-9 volts of DC current applied to them and a resistor to bias the built in FET amplifier, the signal you get from this is still pretty weak so it will need to go through a pre-amp to give you an output signal that's compatible with a line output (headphones) Since the microphone requires a DC bias for power AC coupling is required. You could use MANY simple audio mixing hardware to feed the RF adapter a signal from a microphone though..

One possible source for this type of audio equipment on the cheap is a local Salvation Army or any similar type of thrift store, many people offload older AV equipment, and you'll find quality stuff if you look.

Another easy solution is to use your PC, they almost always have a mic input, and through the mixer in the audio control panel you can cause it to output the microphone to the speakers, which you would just replace with your RF adapter.
 
...Another easy solution is to use your PC, they almost always have a mic input, and through the mixer in the audio control panel you can cause it to output the microphone to the speakers, which you would just replace with your RF adapter.

Wow, I never actually thought of going around it that way. I will actually have to try that. Thanks for that!
 
Because I believe this category is more fitting for the subject...and I don't know how to delete threads so I just left them both up.
 
No, not directly at least, microphone's don't output any signal without power going to them. Typical microphones are electret mics, AKA piezo microphones. They require 2-9 volts of DC current applied to them and a resistor to bias the built in FET amplifier.
No. A piezo mic is a completely different animal. It needs no power and electrically is a capacitor. It produces a signal when it is flexed.
An electret mic is a condenser mic but the 48VDC polarizing voltage used externally with a condenser mic is permanently built into the electret material.


Isn't it fun to jump back and forth beween his identical threads?? I will try not to repeat myself.
 
AG, are you not feeling well? A piezo mic is a completely different animal? It needs no power and is electrically a capacitor?
Piezo elements produce signals when flexed. in an electret mic, that condensor (capacitor) is the same thing, the polarization in an electret mic is from a permanently embeded field in a dielectric subtrate nearby, hence the term electret mic. They all work with the EXACT same excitation element, and are all directly related. A common electret device however has a jfet or mosfet amplier built into the element at the source of the signal to allow the low level piezo signaled to hae a hope of getting anywhere else unaided, hence the required DC bias of an electret mic, it's not for the polarizing voltage, it's to bias the fet element.
 
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Sceadwian,
You can read in Wikipedia about the enormous differences of a rare and old piezo microphone (where a stiff wafer of crystal is flexed) and a modern electret type (where a thin foil or film is vibrated) that is produced by the billions each year. A piezo crystal generates a voltage in its piezo material like a BBQ lighter without using a polarizing voltage. Today they are sensors for electric drums. They can also be driven to produce sound.
An electret mic has a 48V polarizing voltage built-in as a bias voltage for the capacitance between its foil plate and its structure forming a capacitive voltage divider. The do not produce sound.
 
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