SJS132@psuvm.psu.edu (02/10/91)
Well, I saw that a few people wanted to BUY a indicator for their
extentions to show when it was busy ... BUT ... for those that would
rather build one, and save the dough, then here are the plans.
*Note* : I'm not responsible if you hook it up wrong ... I did it, and
it works fine. Also, I origanally go it out of a magazine, which I
have long lost ... but it was published. I don't have an address to
write to, to ask for permission to post it here. If you don't like it,
buy the magazine. I at least did have the name of the author, and do
give him full credit.
Anything I left out??? Oh yeah, there is one place that almost looks
like two lines shoud be connected ... DONT. It is actually overlapping
(ie, a jumper) and could cause problems. That's why, if two lines
are connected, I use 'o' indicate a connection.
Well, thats it ... enjoy, and watch out when stripping those phone
wires ... you can get a nasty jolt if you do it with your TEETH! (like
me!)
Phone Line "Busy" indicator
Taken out of Modern Electronics
November. 1988
Written by: Robert M. Harkey
(I only wrote it up, and condensed it.)
This little circuit is VERY nice to have, especially if you use a
MODEM on a multi-Extention line. It is small enough to be built on a
small circuit board, and then added to the phones on the extension
(PUT IT INSIDE THEM! Its neater and better for the reliability of the
circuit. Compared to if you had the wires hanging out where they can
be ripped out of the phone by a cat or small child.)
Here's the Circuit:
Note:
o is for where a connection |-----------+
has been made... R4 /c |R5
_____/\/\/\___|b <-Q2 /\/\/\
| \e |
R1 /b | ---
o-----/\/\/\/\----o-----|c <-Q1 | Led1
| \e | |
to R3 | |----------------|-----------o
phone /\/\/\/\ | |
| | |
R2 | | |
o----/\/\/\/\-----o------------------------o----|:|:|--+
B1
What does all that mean? Well, here is a list of parts...
R1,R2 : 2.2M ohm Resistors
R3 : 330K Resistor
R4 : 33K Resistor
R5 : 220 ohm Resistor
Q1 : NPN Transitor#> 2N3906
Q2 : NPN Transitor#> 2N3904
B1 : 3V external battery supply (2x AA batteries)
Led1 : General purpose Light emitting diode
All can be found at Radio Shack...
For Beginners:
One particular thing to note: On Q1 and Q2, When I drew them above, it
was hard. So I labeled each with their corresponding E - C - B...
What is ECB?? It stands For Emitter, Collector, Base. I hope I did
them right, Its been a while, and I wasn't sure, but basically, if you
get the right transistor number you don't have to worry, just put it
in the circuit with the E being the little ARROW coming off of the
picture on the back of the Transistor pack.
Good Luck...
Steven Shimatzki RD#1 Box 20-A Dunbar, Pa 15431
InterNet: SJS132@PSUVM.PSU.EDU BBS: (412) 277-0548
Disclaimer: I have nothing to do with the people I know, nor do I know
the people I am with. I just like the money they pay me.