Beehive terminals

[Chuck Guzis]

On 12/31/2005 at 12:17 AM ard at p850ug1.demon.co.uk wrote:

>I thought the touch-tone keypad was 2 transistors, one for the column 
>frequencies, one for the row frequencies. But I've never seen one.

No sir, it used only a single transistor.  Transistors were viewed as the
least reliable part of a telephone and so usage was minimized.  Here's a
schematic of the dial on one of them:

http://www.bellsystemmemorial.com/images/2526bm_schematic_2.gif

I remember learning this from a friend and being more than a little
skeptical.  But 'tis true - a dual mode oscillator.  There's also a
reference on this forum:

http://www.castalk.com/ftopic8083-15.html

I think WE doesn't get nearly enough credit for creating some really
bulletproof designs.

Cheers,
Chuck