rakoczynskij@ncar.ucar.edu (Jurek Rakoczynski) (10/23/90)
A few weeks back, I read where someone was looking for an inexpensive
phone system for the home (play phone for the kids, etc.). It
reminded me of something I built when I lived in a condo. The
neighbors and my wife would talk on the *real* phone quite a bit, so I
decided to become an Alternate Telephone Service supplier. I built a
private telephone system between us (we had a common wall between us).
It's very simple to build with only a few inexpensive components.
How it works:
The +Tip (Grn) and -Ring (Red) lead of the telephones are tied in
series with astandard 9v (transitor) battery. More than enough power
for most/all phones. The sound is so clear you can here a pin drop. :-)
The calling party signals the called party by closing a switch that
operates in series with a battery (Grn or Red lead), one of the
Yel/Blk leads, a buzzer at the called parties phone and to the other
side of the battery.
One picture (200+ ASCII characters) is worth a 1000 words so heres the
ASCII picture:
your house <= | => other house
^
demarkation
point - it's the law :-)
+-BATT-+
| +
+---+ G | G |+---+
------+-------- |G. | ------------+ +| .G| --------+------
| | | R R | | |
To ------|-------- |R. | ------------------- | .R| --------|------ To
Phone | | | Y B | | | Phone
--+---|-------- |Y. | --------\ /-------- | .Y| --------|---+--
| | | | B X Y | | | |
--|---|---+---- |B. | --------/ \-------- | .B| ----+---|---|--
| | | | | | | | | |
| | | +---+ 4 Cond Ca. +---+ | | |
| | | Wall Jack Wall Jack | | |
| | | | | |
+-/-+-O-+ +-O-+-/-+
S1 PB1 PB1 S1
Legend Material List
. = Wire Terminal in Wall Jack 2-S1 Momentary On SPST Push button
G = Green switch - mini
R = Red 1-B1 9V transistor battery &
Y = Yellow snap on connector
B = Black 2-PB1 Piezo buzzer, operate on less
+ = wire splice then 7V.
2-Wall jacks
2-Telephones + cord to wall jack
1 length 4 conductor cable
To clarify the picture: 1. The battery is in series with the Grn lead.
Power to S1/PB1 comes directly from the battery. The polarity of the
battery usually will not matter unless you have a polarity sensitive
phone. Then swap the R/G leads and keep trying. You could located the
battery in either the Red or Green lead. I just picked green for
convenience of the picture.
2. There is a cross-over in the Y/B leads between the wall jacks to
keep the termination of S1/PB1 the same on both ends. It makes it easier.
When I originally built this, I mounted the buzzer and battery on the
wall jack, and the switch on the phone (by drilling a hole in the
phone). You could try mounting the switch and buzzer:
1. both in the phone, or
2. both on an external box with a seperate lead into the phone, or
3. both on an external box that interfaces between the wall jack and phone
so you don't have to modify the phones.
It worked for 1.5 years on the original battery before I moved and it
was still going strong - like that bunny :-).
If you have any questions, you can try sending me mail, but I not sure
how to email out of here. I guess I should learn.
First time poster: Standard apologies apply for header errors, etc..
No .sig yet. Standard disclaimers.