31 Dec
2005
31 Dec
'05
1:18 p.m.
On 12/31/2005 at 12:17 AM ard at p850ug1.demon.co.uk wrote:
I stnad corrected.
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:
Interesting. I think the Post Office in England thought the same way at
one point. They had a little transistorised signal tracer with a 4 (?)
transsitor amplifier in it. Most of the amplifier was a potted module,
but the transistors were mounted on top and soldered to pins sticking out
of the potting compound so they could be replaced.
I think WE doesn't get nearly enough credit for
creating some really
bulletproof designs.
I find it a great pity that now that transistors have become so cheap
(particularly when in ICs), most people don't care how many are used, and
most modern designs use far too many of them. It's amazing what could be
done with 2 or 3 of the things, but those clever designs have been mostly
forgotten.
-tony