Forums

Phone in use circuit not working

Started by steve February 28, 2013
I tested and built the following circuit.

http://www.circuitstoday.com/telephone-in-use-indicator

It all worked fine untill I tried to test it by calling into my phone.
(the one test I didnt do before I soldered it all together)

What happens is taht the phone rings for a about 1/2 a ring then stops ringing.
To my surprise when I life the phone up the line is alive eg. Its like the device has answered the phone.

I think that the circuit must be drawing too much power and then telling the phone that it has been answered, because the voltage has gone down. 

I have had to replace the Transistors with NTE199, which according to the book are the same. I have also used a rectifier that is a 2 amp 400v SIP 2KBP04M-1.
Im wondering if I used a different rectifier if that would change the results?

I recognize that your not suppse to take power from the phone co. but I would like to get this circuit working. Can anyone tell me why its not working.
thanks.
steve says...

 > What happens is taht the phone rings for a about 1/2 a
 > ring then stops ringing. To my surprise when I life the
 > phone up the line is alive eg. Its like the device has
 > answered the phone.

 > I think that the circuit must be drawing too much power
 > and then telling the phone that it has been answered,
 > because the voltage has gone down.

That sounds right.  The phone company senses an off-hook
state based on DC current passing through the local loop.
So your explanation makes sense.

I think your part substitutions are correct.  But I wonder
if you have the bridge rectifier wired correctly - the phone
lines connected to the ~ pins.  Or, could that part be
faulty?

If everything is wired correctly, try removing R4 from the
circuit and see if ringing works properly then.  If it does,
then you may just need a higher value resistor for R1.

Actually, I don't much care for the circuit. During each
cycle of the ring signal, the voltage on your circuit will
go to zero.  It won't go negative because of the rectifier,
but it will go to zero.  As it gets near zero, then again as
it comes back up, Q2 will turn on for a bit, and current
will flow, until the voltage gets high enough to turn on Q1,
which will turn off Q2.  But during that Q2-on period, maybe
enough current will flow to signal an off-hook to the
central office.  Well, I'm clearly just guessing, but I find
myself wanting to put a capacitor from the base of Q1 to
ground.

Anyway, good luck.

Thank you for your comments.

Well I have wired the phone line to the middle pins on the SIP [ + | | - ]
And + to plus and - to Neg of the diagram.

Thanks for the tips. I will try them.

By the way one thing. The diagram calls for R2 to be 33k. But a comment on =
the bottom says that the value should be the same as R1 3.3. So I made R2 3=
.3. I asumed that the poster was right, because I know how scematics get sc=
rewed up some times. In your opinion should R2 be 3.3k or 33k. Maybe thats =
whats wrong?
Regards.
steve says...

 > Well I have wired the phone line to the middle pins on
 > the SIP [ + | | - ] And + to plus and - to Neg of the
 > diagram.

Yes, I think that's right.

 > By the way one thing. The diagram calls for R2 to be
 > 33k. But a comment on the bottom says that the value
 > should be the same as R1 3.3. So I made R2 3.3. I asumed
 > that the poster was right, because I know how scematics
 > get screwed up some times. In your opinion should R2 be
 > 3.3k or 33k. Maybe thats whats wrong?

Well, using 33k will make the circuit draw less current, but
the green LED probably will not light up enough to be
visible.  But of course you really don't need the green LED,
just the red one.

My concern is that the circuit just draws too much current,
and therefore shows as off-hook.  I would try it at 33k, and
take the green LED out (or just temporarily jumper across
it, and see if it works.  Beyond that, you could increase
the resistance of R1, but then that will make the red LED
dimmer.

There is another version of this circuit that uses MOSFETs
instead of NPN transistors, and all but the LED resistor are
in megohms, so it draws very little current when on-hook.
That's because the MOSFETs switch based on voltage instead
of current.

http://www.zen22142.zen.co.uk/Circuits/Misc/tiuc.htm


steve wrote:
> I tested and built the following circuit. > > http://www.circuitstoday.com/telephone-in-use-indicator > > It all worked fine untill I tried to test it by calling into my phone. > (the one test I didnt do before I soldered it all together) > > What happens is taht the phone rings for a about 1/2 a ring then stops ringing. > To my surprise when I life the phone up the line is alive eg. Its like the device has answered the phone. > > I think that the circuit must be drawing too much power and then telling the phone that it has been answered, because the voltage has gone down. > > I have had to replace the Transistors with NTE199, which according to the book are the same. I have also used a rectifier that is a 2 amp 400v SIP 2KBP04M-1. > Im wondering if I used a different rectifier if that would change the results? > > I recognize that your not suppse to take power from the phone co. but I would like to get this circuit working. Can anyone tell me why its not working. > thanks.
I think some one gave you some bad transistor numbers.. THe phone system in the US rings at around 100 Volts AC and on hook is around 50Volts. Off hook may give you around 10 volts and it depends on how many phones you have at one time off hook. The 2N3392 can only handle 25Volts and it may work if you can insure that the unit will switch on in time to load it down. Further more, the other transistor will be sitting there with this 50v (on hook), leaking through the collector. The NTE199 replacement isn't much better, it has a 70V limit at best and most likely will work find when on hook, but when it rings, you can expect some leaking to be taking place. You first need to get HV transistors. Try getting some 2N5550 transistors, or the 2N5551 which is a little higher.. Mouser.com has 2N5551 for 0.78 ech and they have over 3k in stock. Jamie
Peabody wrote:

> steve says... > > > Well I have wired the phone line to the middle pins on > > the SIP [ + | | - ] And + to plus and - to Neg of the > > diagram. > > Yes, I think that's right. > > > By the way one thing. The diagram calls for R2 to be > > 33k. But a comment on the bottom says that the value > > should be the same as R1 3.3. So I made R2 3.3. I asumed > > that the poster was right, because I know how scematics > > get screwed up some times. In your opinion should R2 be > > 3.3k or 33k. Maybe thats whats wrong? > > Well, using 33k will make the circuit draw less current, but > the green LED probably will not light up enough to be > visible. But of course you really don't need the green LED, > just the red one. > > My concern is that the circuit just draws too much current, > and therefore shows as off-hook. I would try it at 33k, and > take the green LED out (or just temporarily jumper across > it, and see if it works. Beyond that, you could increase > the resistance of R1, but then that will make the red LED > dimmer. > > There is another version of this circuit that uses MOSFETs > instead of NPN transistors, and all but the LED resistor are > in megohms, so it draws very little current when on-hook. > That's because the MOSFETs switch based on voltage instead > of current. > > http://www.zen22142.zen.co.uk/Circuits/Misc/tiuc.htm > >
That one would most likely work better, at least the transistors are rated at 200V, which is your biggest problem with the first circuit.. Also this circuit has much less load since it seems to only work when off hook. Jamie
On 2/28/2013 6:30 PM, Jamie wrote:
> Peabody wrote: > >> steve says... >> >> > Well I have wired the phone line to the middle pins on >> > the SIP [ + | | - ] And + to plus and - to Neg of the >> > diagram. >> >> Yes, I think that's right. >> >> > By the way one thing. The diagram calls for R2 to be >> > 33k. But a comment on the bottom says that the value >> > should be the same as R1 3.3. So I made R2 3.3. I asumed >> > that the poster was right, because I know how scematics >> > get screwed up some times. In your opinion should R2 be >> > 3.3k or 33k. Maybe thats whats wrong? >> >> Well, using 33k will make the circuit draw less current, but >> the green LED probably will not light up enough to be >> visible. But of course you really don't need the green LED, >> just the red one. >> >> My concern is that the circuit just draws too much current, >> and therefore shows as off-hook. I would try it at 33k, and >> take the green LED out (or just temporarily jumper across >> it, and see if it works. Beyond that, you could increase >> the resistance of R1, but then that will make the red LED >> dimmer. >> >> There is another version of this circuit that uses MOSFETs >> instead of NPN transistors, and all but the LED resistor are >> in megohms, so it draws very little current when on-hook. >> That's because the MOSFETs switch based on voltage instead >> of current. >> >> http://www.zen22142.zen.co.uk/Circuits/Misc/tiuc.htm >> >> > That one would most likely work better, at least the transistors > are rated at 200V, which is your biggest problem with the first > circuit.. > > Also this circuit has much less load since it seems to only work > when off hook. > > Jamie >
Here's one I used for years without problem. Similar to what Peabody posted, one less FET. http://i395.photobucket.com/albums/pp37/Qmavam/PhoneLineInUseIndicator_zpsf78c4525.png I can't find the original URL. Mikek
amdx wrote:

> On 2/28/2013 6:30 PM, Jamie wrote: > >> Peabody wrote: >> >>> steve says... >>> >>> > Well I have wired the phone line to the middle pins on >>> > the SIP [ + | | - ] And + to plus and - to Neg of the >>> > diagram. >>> >>> Yes, I think that's right. >>> >>> > By the way one thing. The diagram calls for R2 to be >>> > 33k. But a comment on the bottom says that the value >>> > should be the same as R1 3.3. So I made R2 3.3. I asumed >>> > that the poster was right, because I know how scematics >>> > get screwed up some times. In your opinion should R2 be >>> > 3.3k or 33k. Maybe thats whats wrong? >>> >>> Well, using 33k will make the circuit draw less current, but >>> the green LED probably will not light up enough to be >>> visible. But of course you really don't need the green LED, >>> just the red one. >>> >>> My concern is that the circuit just draws too much current, >>> and therefore shows as off-hook. I would try it at 33k, and >>> take the green LED out (or just temporarily jumper across >>> it, and see if it works. Beyond that, you could increase >>> the resistance of R1, but then that will make the red LED >>> dimmer. >>> >>> There is another version of this circuit that uses MOSFETs >>> instead of NPN transistors, and all but the LED resistor are >>> in megohms, so it draws very little current when on-hook. >>> That's because the MOSFETs switch based on voltage instead >>> of current. >>> >>> http://www.zen22142.zen.co.uk/Circuits/Misc/tiuc.htm >>> >>> >> That one would most likely work better, at least the transistors >> are rated at 200V, which is your biggest problem with the first >> circuit.. >> >> Also this circuit has much less load since it seems to only work >> when off hook. >> >> Jamie >> > Here's one I used for years without problem. > Similar to what Peabody posted, one less FET. > http://i395.photobucket.com/albums/pp37/Qmavam/PhoneLineInUseIndicator_zpsf78c4525.png > > I can't find the original URL. > Mikek >
I remember buying an off hook relay module for a phone line from radio shaft years ago, back in the old days, it never worked. would never switch on. Also, they stopped selling them. Must of been a reason for it :) Some times it is more sensible to buy ready made over making it. Jamie
amdx says...

 > Similar to what Peabody posted, one less FET.

>http://i395.photobucket.com/albums/pp37/Qmavam/PhoneLineInUseIndic
ator_zpsf78c4525.png Yes, and that has the capacitor I kept wanting to put into the first circuit. That should delay the turn-on of the FET enough to keep the LED off during ringing.
On 2/28/13 11:22 AM, steve wrote:
> I tested and built the following circuit. > > http://www.circuitstoday.com/telephone-in-use-indicator > > It all worked fine untill I tried to test it by calling into my phone. > (the one test I didnt do before I soldered it all together) > > What happens is taht the phone rings for a about 1/2 a ring then stops ringing. > To my surprise when I life the phone up the line is alive eg. Its like the device has answered the phone. > > I think that the circuit must be drawing too much power and then telling the phone that it has been answered, because the voltage has gone down. > > I have had to replace the Transistors with NTE199, which according to the book are the same. I have also used a rectifier that is a 2 amp 400v SIP 2KBP04M-1. > Im wondering if I used a different rectifier if that would change the results? > > I recognize that your not suppse to take power from the phone co. but I would like to get this circuit working. Can anyone tell me why its not working. > thanks. >
I remember as a teenager, I was playing around with the phone line. I learned two things. One, if you hook the right resistance across the line, incoming calls get a "busy" signal, but you can still make outgoing calls. Two, when someone is calling you, you can get a jolt if you're holding both ends of the line. So, when the phone rings, you get a 60V AC signal. Perhaps you need slightly more resistance in the line. Unless D2 is already too dim, I'd try changing R1 to a higher resistance.