[EMAIL PROTECTED] writes: > I also had a friend who discovered that old pay telephones used to use > the sound of the falling coins striking a bell to determine whether the > money was properly deposited in the phone.
Payphones later used frequency-shifted DTMF tones to signal the deposit of each coin. I changed the crystal in an accoustic speed dialer to make that set of tones... worked quite well until they rigged the phones to mute the mic until money was deposited. And now it is all done as digital signaling out of the voice-frequency range. Steve WD8DAS [EMAIL PROTECTED] http://www.qsl.net/wd8das --------------------------------------- Radio is your best entertainment value. ---------------------------------------
