Re: Use old phone as microphone

Joerg wrote: 
Hello Richard,

These microphones usually behave as a variable resistor, So you need a
voltage source, and a dropper resistor to act as a potential divider, and
give you a voltage output as the resistance varies. The microphone can be
used as either resistor in the divider. Using it as the bottom resistor,
allows the casing to be connected to ground. Either connection results in
a significant DC voltage being present on the output. This is 'OK' if the
line input is AC coupled, but otherwise a capacitor must be included in
the circuit as shown.


Carbon particle mikes also require that the phone sees a certain line current, usually around 25mA.

Regards, Joerg


Thanks

I didn't know that.

Really need to establish what sort of mike the OP has in his handset.

The idea could be used for Skype - if there were a way of telling the
package that the phone had been answered when the phone was taken off the hook.
.

Relevant Pages

  • Re: Transistor biasing
    ... > upsetting the base voltage ... single base bias resitor only, ... Using potential divider bias, ... resistor, I can't understand how that would stabilize Ic. ...
    (sci.electronics.basics)
  • Re: Use old phone as microphone
    ... voltage source, and a dropper resistor to act as a potential divider, and give you a voltage output as the resistance varies. ... The microphone can be used as either resistor in the divider. ...
    (sci.electronics.design)
  • Re: P2B-DS and generic slotkets
    ... The slockets are labeled "Cpu Card ... processors are requesting 2.0 volts instead of 1.65 volts. ... If R3 is a 56 ohm resistor, ... With regard to the voltage being requested, ...
    (alt.comp.periphs.mainboard.asus)
  • Re: Einsteins Doppler equation wrong?
    ... the voltage is zero, i.e dE/dt is at its greatest, and ceases when the ... short circuit. ... :>: consisted of a connector with a small resistor tying the core ... :>: Without the terminator, the thinnet cable spits back echoes into ...
    (sci.physics.relativity)
  • Re: P2B-DS and generic slotkets
    ... processors are requesting 2.0 volts instead of 1.65 volts. ... If R3 is a 56 ohm resistor, ... With regard to the voltage being requested, ... you sure the slocket doesn't have a way to modify the VID ...
    (alt.comp.periphs.mainboard.asus)
Quantcast