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Telephone in use indicator Help

S

steve

Jan 1, 1970
0
I have made the circuit at the link below.

http://www.techlib.com/electronics/telephone.html

Its the first one in the list "Telephone in use indicator"

It works fine accept that when there is no one on the phone the LED
glows a little. (On hook I think they call it)

What can I do to stop it from glowing and using up the battery. I tried
to put a 500 ohm resister just after the LED between the LED and
positive eg LED --[500]--+ . This did not change anything.
Also is it right that when the circuit is not connected to the phone
system but the battery installed that the LED blinks. It stops blinking
when I hook it up to the phone system (it just glows a little)

Thanks
 
M

mc

Jan 1, 1970
0
steve said:
I have made the circuit at the link below.

http://www.techlib.com/electronics/telephone.html

Its the first one in the list "Telephone in use indicator"

It works fine accept that when there is no one on the phone the LED
glows a little. (On hook I think they call it)
What can I do to stop it from glowing and using up the battery. I tried
to put a 500 ohm resister just after the LED between the LED and
positive eg LED --[500]--+ . This did not change anything.

The first thing I'd do is use a voltmeter to measure the voltage across the
phone line. It should be above 45 volts on-hook, below 10 volts off-hook.
If that's not the case, let us know.

The second thing would be to look for a wiring error in the input circuit
(the diodes, the 22 M and 1 M resistors, and the first transistor). Maybe
even a defective first transistor.
Also is it right that when the circuit is not connected to the phone
system but the battery installed that the LED blinks. It stops blinking
when I hook it up to the phone system (it just glows a little)

Yes. When disconnected, it is picking up stray electrical fields from its
surroundings.

Frankly, that strikes me as a very complicated circuit to do a simple job.
I'm sure there are simpler designs, but if this one works for other people,
it should work for you.
 
S

steve

Jan 1, 1970
0
Thanks for your comments.

I tested the voltage On Hook its 51 VDC. Off Hook its 51 VCD.

I have tested the four Diodes they seem to be ok. Closed one way .5 to
..6 Ohms the other way. If I understand it right.

I have gone over the circuit one more time looking for human error.
Cant seem to see anything wrong.

The one thing I did not mention was that I am using the 2n4401 instead
of the MPSA-18, as the schematic suggests I can do.

I must say when I tested the resisters they do vary a lot when your at
the 22M size. My little digital meter reads them anywhere from about 21
to about 25. My meter has a 20M scale and then a 200. So I have to set
it on the 200M scale to test 22M. I figure its doing pretty good to get
in anywhere near 22M.

Short of any other answers I could test the Transistors. But IM not
always sure I know what to look for or how acurate it is on my little
Digital MM. (which is all I have being a Novice.)

The reason I chose this circuit I suppose is because it looked
relatively simple and used an external power source which should last
for some time. Im always wary of all the warnings about causing
problems with stealing power from the poor phone company. And possible
other issues that can come up.

Any thoughts?

Regards
 
S

steve

Jan 1, 1970
0
steve said:
Thanks for your comments.

I tested the voltage On Hook its 51 VDC. Off Hook its 51 VCD.

Correction..

SORRY I MIS WROTE

I mean On hook is 51vdc and off hook is 10.9vdc

sorry
 
M

mc

Jan 1, 1970
0
steve said:
Thanks for your comments.

I tested the voltage On Hook its 51 VDC. Off Hook its 51 VCD.

Same voltage both ways? No...
I have tested the four Diodes they seem to be ok. Closed one way .5 to
.6 Ohms the other way. If I understand it right.

Open one way, 0.6 volt (the diode test range on your meter reads in volts,
not ohms), is correct.
I have gone over the circuit one more time looking for human error.
Cant seem to see anything wrong.

The one thing I did not mention was that I am using the 2n4401 instead
of the MPSA-18, as the schematic suggests I can do.

2N4401 is reliable and should work.
I must say when I tested the resisters they do vary a lot when your at
the 22M size. My little digital meter reads them anywhere from about 21
to about 25. My meter has a 20M scale and then a 200. So I have to set
it on the 200M scale to test 22M. I figure its doing pretty good to get
in anywhere near 22M.

It's the meter's problem, not the resistors... It's hard to measure
resistances that high. I doubt there is anything wrong with the resistors.
Short of any other answers I could test the Transistors. But IM not
always sure I know what to look for or how acurate it is on my little
Digital MM. (which is all I have being a Novice.)

Does it have an hFE (transistor gain) measurement? If so, try that.
The reason I chose this circuit I suppose is because it looked
relatively simple and used an external power source which should last
for some time. Im always wary of all the warnings about causing
problems with stealing power from the poor phone company. And possible
other issues that can come up.

Any thoughts?

It looks like a reliable design, although a bit on the complicated side.

Please check over and over again for wiring errors. Even the best of us
make plenty of them.
 
S

steve

Jan 1, 1970
0
I'll check the transistors. Yes my meter does have hFE measurement.
Perhaps as I test them It will give me another opportunity to check
that every thing hooked up right.

I'll get back with hFE readings.
 
R

Rich Grise

Jan 1, 1970
0
I have made the circuit at the link below.

http://www.techlib.com/electronics/telephone.html

Its the first one in the list "Telephone in use indicator"

It works fine accept that when there is no one on the phone the LED
glows a little. (On hook I think they call it)

What can I do to stop it from glowing and using up the battery. I tried
to put a 500 ohm resister just after the LED between the LED and
positive eg LED --[500]--+ . This did not change anything.
Also is it right that when the circuit is not connected to the phone
system but the battery installed that the LED blinks. It stops blinking
when I hook it up to the phone system (it just glows a little)

Is this thing supposed to flash just when the phone is off-hook? That's
not the way it's done anywhere else, at least in the USA. When you're
off-hook, it's supposed to be steady on, and it flashes when you put the
line on hold. (to put a phone line on hole, I've been told, just put a
600 ohm resistor across the line, and disconnect the phone, of course.)

Frankly, overall, the circuit looks a little flaky to me, but I'm just
a tech. ;-)

Good Luck!
Rich
 
J

Jonathan Kirwan

Jan 1, 1970
0
<snip>
The reason I chose this circuit I suppose is because it looked
relatively simple and used an external power source which should last
for some time. Im always wary of all the warnings about causing
problems with stealing power from the poor phone company. And possible
other issues that can come up.

I learned that you need to be wary about such things, too. I believe
that the total loading on the line when on-hook should be greater than
about 5M ohm. That's not so easy to achieve.

I did take the trouble, though, to design a circuit that presents a
constant load of 40Mohm when the home is on-hook and pulls a constant
current of 400uA to drive an LED when off-hook (I use a very low
current voltage trigger to set the threshold.) I have another that
presents about 40Mohm at all times and blinks a tiny LED slowly at low
voltage and faster at high voltage. That one is probably better, as
it doesn't ever load the line much.

I suspect that a professional could do better still, too, and adhere
well to the loading specs. The reason I targeted 40Mohm is that I
wanted to use a couple of them on the line.

Jon
 
S

steve

Jan 1, 1970
0
I tested the transisters

reading from left to right
the first 2N4401 is hF 266
the second 2N4403 is hf 287
the third 2N4401 is hf 241.

Not sure, Im guessing these numbers are ok.
 
M

mc

Jan 1, 1970
0
steve said:
I tested the transisters

reading from left to right
the first 2N4401 is hF 266
the second 2N4403 is hf 287
the third 2N4401 is hf 241.

Not sure, Im guessing these numbers are ok.

Yes, definitely. They are in fact toward the high end of the range, and
it's conceivable the designer of the circuit had lower ones, and this might
have affected the performance of the unit in some way. You might try
swapping out the first transistor, just to see what happens.

Also look for bad solder joints.
 
J

Jamie

Jan 1, 1970
0
steve said:
Thanks for your comments.

I tested the voltage On Hook its 51 VDC. Off Hook its 51 VCD.

I have tested the four Diodes they seem to be ok. Closed one way .5 to
.6 Ohms the other way. If I understand it right.

I have gone over the circuit one more time looking for human error.
Cant seem to see anything wrong.

The one thing I did not mention was that I am using the 2n4401 instead
of the MPSA-18, as the schematic suggests I can do.

I must say when I tested the resisters they do vary a lot when your at
the 22M size. My little digital meter reads them anywhere from about 21
to about 25. My meter has a 20M scale and then a 200. So I have to set
it on the 200M scale to test 22M. I figure its doing pretty good to get
in anywhere near 22M.

Short of any other answers I could test the Transistors. But IM not
always sure I know what to look for or how acurate it is on my little
Digital MM. (which is all I have being a Novice.)

The reason I chose this circuit I suppose is because it looked
relatively simple and used an external power source which should last
for some time. Im always wary of all the warnings about causing
problems with stealing power from the poor phone company. And possible
other issues that can come up.

Any thoughts?

Regards
my seven cents worth!
a few years ago i did some house hold phone research
for a project of mine!. this is what we have..

When ringing,
100 V AC!
when not ringing and phone on the hook (no line connection).
50 V DC of a fixed polarity.
when the phone is taken off the hook, it drops in the area of
6..12 volts of the same polarity if memory serves.
when dialing with the old rotary, this turns into a 0 to 6..9 volt
pulse., the Tones simply modulate the line like does the voice..
and the last and most important is this, when the party on the other
end picks up!, the polarity changes on the line!
i guess this is how answering machines know when the party is still
there because when they hang up the polarity switches back.
don't know if it is still that way in the USA but i would guess it is.
 
J

Jamie

Jan 1, 1970
0
mc said:
Ah! Much better.
and don't forget, the polarity reverses depending
on the state of the connection to your party!
 
E

ehsjr

Jan 1, 1970
0
steve said:
I have made the circuit at the link below.

http://www.techlib.com/electronics/telephone.html

Its the first one in the list "Telephone in use indicator"

It works fine accept that when there is no one on the phone the LED
glows a little. (On hook I think they call it)

What can I do to stop it from glowing and using up the battery. I tried
to put a 500 ohm resister just after the LED between the LED and
positive eg LED --[500]--+ . This did not change anything.
Also is it right that when the circuit is not connected to the phone
system but the battery installed that the LED blinks. It stops blinking
when I hook it up to the phone system (it just glows a little)

Thanks

Remove the 2N4401 nearest the battery. Does the LED
still glow? If so you are seeing the unavoidable
(in this circuit) current from the battery + through
the LED and the 1 meg and 2.2 meg series resistor to
the - of the battery. That current is very low -
9/3300000 which is roughly 3 uA. The lowest I have
seen a LED glow is 27 uA, and then I had to look at
it *very* closely.

Anyway, I expect you will not see it glow with the
transistor removed. If it does not glow, put the
transistor back in, and add a 1 meg resistor from
its base to ground. If it does glow, check the
resistance (with the thing disconnected and the
battery removed) from the junction of the two
1 meg resistors to ground.

Ed
 
S

steve

Jan 1, 1970
0
Results

Removed 3erd tr. Nearest Battery. (4401)
Very subtle glow when (circuit not connect to telephone)
Connect same circuit to phone line
On Hook seems to glow
Off hook dims
(of course in the above test there is no flashing)

Added resister and put back tr.
When I hook up to phone line. there is a glow ON HOOK.

Checking the resistence from the juncktion of the two 1 Meg Reisisters.

Im not sure what you mean by with the thing disconnected. Im asuming
you mean not connected to the phone line.

With your 1 Meg R. in place it settles down to about 3.2M
W/out the addition of your 1M R. It grows from about 1.4 to 2.7 then
back down again to 1.4 backup to 2.7.(roughly)
I guess this has to do with the capacitor. charging and releasing??

Those are my results.
 
D

Don Bowey

Jan 1, 1970
0
my seven cents worth!
a few years ago i did some house hold phone research
for a project of mine!. this is what we have..

When ringing,
100 V AC!
when not ringing and phone on the hook (no line connection).
50 V DC of a fixed polarity.
when the phone is taken off the hook, it drops in the area of
6..12 volts of the same polarity if memory serves.
when dialing with the old rotary, this turns into a 0 to 6..9 volt
pulse., the Tones simply modulate the line like does the voice..
and the last and most important is this, when the party on the other
end picks up!, the polarity changes on the line!
i guess this is how answering machines know when the party is still
there because when they hang up the polarity switches back.
don't know if it is still that way in the USA but i would guess it is.

A POTS line in the US does not change polarity when the "far end" answers.

Don
 
E

ehsjr

Jan 1, 1970
0
steve said:
Results

Removed 3erd tr. Nearest Battery. (4401)
Very subtle glow when (circuit not connect to telephone)

Ok. Get a different circuit. You've got roughly 3 uA
current which is unavoidable with this circuit, and it
makes your LED glow. You either have to live with
that or change to a different circuit. I can't see
any glow with only 3 uA through an LED, but it is your
eyes you need to satisfy, not mine.

Ed
 
D

DecaturTxCowboy

Jan 1, 1970
0
Jamie said:
and the last and most important is this, when the party on the other
end picks up!, the polarity changes on the line!
i guess this is how answering machines know when the party is still
there because when they hang up the polarity switches back.
don't know if it is still that way in the USA but i would guess it is.

The polarity doesn't change for the duration of the call, but it does
after the far end hangs up. Its called reverse answer supervision. When
you call and an answering machine answers - and then you hangup, the
Central Office momentarily reverses the polarity back towards the called
party and the answering machine knows to hang up.
 
S

steve

Jan 1, 1970
0
Thanks I guess that waht I will have to do.
Yes the glow is faint. I turn off the light int he room Im in and there
it is glowing. I have tried various resistors in various places of
various sizes. I can reduce it but not get rid of it completely.

Rats. Just when things are working they dont.

Regards
 
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