Mapping voice and voltage levels to frequency

[berrymaleek]

My project is about creating a transmitter using the low frequency range (30kHz -300kHz), I am in need of of the right circuits to put together that would map both the voice and digits to frequency, that is, for every sample inputted into the system through a mic condenser for example, frequency is being generated and for the digits, for every key pressed, the voltage levels are converted to frequency and can be transmitted at low frequency range. I hope the little explanation given gives an idea of what I am trying to talk about and any help what so ever will be really appreciated.

 

[MikeMl]

Key pressed to specific frequency is easy, but this a very primitive way of encoding a digital message. Look at standard methods that computers communicate...

Voice requires using a standard modulation technique, either Frequency Modulation (FM) or Amplitude Modulation (AM), techniques which have existed for most of a century...

 

[unclejed613]

on those low frequencies, FM is probably a bad idea because of the ratio of operation frequency to the amount of frequency change (deviation) required for an intelligible signal. AM and double sideband are both very easy to do (difficulty on a scale of 1-10, AM is about a 2, DSB is about a 3 or 4). for AM and DSB, your bandwidth is going to depend on where you set your cutoff frequency for the audio, and the bandwidth will be equal to twice the audio cutoff frequency. for receiving, AM demodulation is simple, requiring only a diode and filter circuit, DSB can use the same circuit as an AM detector, but requires injecting a local carrier wave to make it demodulate properly.