Phone in Use Indicator

[princessphone]

Hello there. I've been a bit bored lately and needed a project. Pulled out my old book: "Telephone Projects for the Evil Genius" and wanted to build a "Phone in Use Indicator" (page 124). Its very basic but I can't get it to work. I tried it several years ago but gave up. When the line is available a green LED should be on, and a red LED when the line is occupied. For me both lights are on when the line is free and all go out when occupied. I've rechecked the wiring, soldering, diagram etc. to no avail. Even set it up on a "bread board". The whole project uses 4 diodes (for the polarity rectification) plus 5 resisters, 2 LED lights and 2 transistors. Has the Bell System changed something that affects my service? I live in Ontario, Canada. Also have internet service with Bell through the phone wires. When I was a bit younger, like in the sixties, I assembled my Hi Fi receiver and amplifier Heathkit AA-15 and AJ15. Wharfedale speakers and Dual 1229 turntable. The system still works and sounds great. I took up ROCK in college - besides space.
Any comment would be greatly appreciated. Oh yes I forgot, I do have a Viking ring booster incorporated in my phone system, however I tested my contraption at my neighbour's house with same results.
Thanks, John DeJonge       

[RB]

Hi John.
It sounds like one of your led's is workin fine.
The other one, seems to be in parallel with the first one???
You are needing a flip/flop type result in your second Led.
I know that book, but do not know the schematic.
Maybe you could provide?
It appears, that you have an Led, "GRN", responding to line being open. A low input to the transistor, if you will.
And a "Red" Led, responding to the line being closed, A High input on the transistor, if you will.
There are examples of Led lites that indicate DC polarity, that is the basis for your device.
All this is assuming the transistors are driving the Led's.
Or, I could be WAAAAAAAAAAAAy out in left field.
You could also achieve your goal with a relay...
When the loop closes, the relay fires, and switches the lite from grn to red...
Good luck

[princessphone]

Hello RB. Thanks for response. I'm a bit challenged posting pictures however here's a website that shows an identical schematic drawing with the exact values of components.  www.circuitstoday.com/telephone-in-use-indicator  I hope that you can find it and let me know what you think.  Thanks again.  John   

[dsk]

I read: "The circuit is powered from the phone line itself and no external power supply is required."  That may be on the edge of what the line sensors in the exchange will accept.  It may work on some lines, and fail on others. 

dsk

[tubaman]

If both LEDs are on when on-hook then Q2 isn't being turned on hard enough. Depending on the LEDs you've used it may be trying to pull too much current from the line?

[countryman]

As I understand it the device does not seize the line, but the phone still works as it should?
It is a voltage indicator. A voltage around 10...12 V should trigger Q1 through a very small current through the green LED (not enough to light it up). Full line voltage of 48 V then also triggers Q2, activating the green LED and putting the basis of Q1 on low level, so the red LED extinguishes.
Possibly the LEDs of the time when the circuit appeared were not as efficient, pulling more current before lighting up. Try putting 1 kOhm across the green LED?
It might also have to do with your DSL service, using high frequency to transmit the data.
Check the voltages inside the circuit when on and off hook. >0.5...0.6 Volt on the transistor basis should make it conductive and the light should come on. Any small NPN transistor should work here. I have not tested the circuit, it might as well have a design flaw.

[princessphone]

Thank you all for your shown interest. Here's The circuit description from my Evil Genius book.

"When all the phones are on-hook, transistor Q2's base is turned on by a voltage divider switch circuit, which consists of R3 and R5. Note that the value for R5 causes the device to switch over at about 9 V. This can be changed to facilitate other voltage levels if desired. Transistor Q2 allows current to flow through R2 and LED2 or D6, indicating that the phone line is not in use. It also effectively grounds the base of Q1 and forces LED1 or D5 to remain off. When the voltage drops because the phone goes off-hook, Q2 stops conducting, allowing a small flow of current from R2, D6, and R4 to Q1's base. When that occurs, Q1 conducts, energizing D5, and D6 is deprived of sufficient current to light up. The bridge rectifier compensates for a possible reversal between the tip and ring wires, and rectifies the ring signal to power the circuit".

I hope that this helps to help me find a solution.  John

[princessphone]

In my previous description D5 should read as D2 (the red LED) and D6 should read as D3 (the Green LED). One diagram labels the bridge as D1,D2,D,D4, and the 2 LED's D5, D6. And another diagram labels the whole bridge as D1, hence the The LED diodes D2 and D3.
John 

[princessphone]

I kinda wish that the author of said project had supplied the specs for the LED light bulbs. I've tried two different sizes, same results. I don't know the specs on them. I'll try to find out. I wonder if incandescent bulbs would work? As far as I know they don't care if its AC or DC.

[Key2871]

Can you post a schematic of the circuit?
And LEDs are not light bulbs, they are light emitting diodes.

[countryman]

Incandescent bulbs would draw too much power and seize the line.
@Key2871, the diagram is already given in the thread, scroll up a little.

[Key2871]

Whoops missed it.. That's the same I saw online.

[RB]

Led's will work with either AC, or DC. they are, in fact, a diode.
with AC, the Led will flicker, and annoy the s#!t out of you, lol.
So they work better with DC

[princessphone]

Hi there. Still struggling with this "simple, basic" project. What I've done so far is simply removed the red LED. Now the green LED stays on when the line is free (on-hook), and when busy/occupied (off-hook) the green LED turns off. Not exactly what I wanted. Any further suggestions would be appreciated.
John   

[Key2871]

Sounds like a bad transistor for the red led.
Or are you using a wrong one?
They are both supposed to be NPN, but if one is incorrect that would account for the circuit not working right. And there is a 3.3 and another 330 ohm resistor.
If the tolerance is too far out of spec that could account for it.