3 ms·
I don't know which came first, but it might have been to make manufacturing easier give the signaling scheme keypad phones used: when you press a key, two sine
by kd5bjo 11y ago
I don't know which came first, but it might have been to make manufacturing easier give the signaling scheme keypad phones used: when you press a key, two sine waves are generated -- one represents the row and the other the column. There's two groups of 4 frequencies for 16 possible buttons; some radios have an extra column with A-D keys for the extra tones.
- DanBC 11y agoSome military phones used the extra keys as part of autovon. https://en.wikipedia.org/wiki/Autovon https://en.wikipedia.org/wiki/Autovon > The Automatic Voice Network (AUTOVON) was a world-wide American military telephone system. The system was built starting in 1963,