Is this possible to do?

[SparkyCal]

I have hunted around the net, and have found various schematics that may do the following, however, I am looking for a simple way of doing it using parts that are commonly available.

I am looking for a way to hook up a LED so that whenever our phone line is in use, it lights up and stays lit until the line is no longer inn use.

Thank-you

By the way- our phones at home are cordless phones, hooked up to an internet based service (MagicJack).

This is sort of close, but it turns off after 3 minutes. I'd like it to stay on until the phone line is hung up. https://www.electroschematics.com/telephone-lamp/

Presently, when the phone is in use, other phones that are in their cradles show the text "Line in Use" on their display. But the display does not light up, and it is hard to see the text from afar. I want something that can be easily seen.

 

[SparkyCal]

I found this one, which looks easier- but what is a 2A Bridge?

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

 

[Bluejets]

Bridge is a 2A bridge rectifier and (as shown) is made up of 4 diodes.
I would imagine this is made for the old style copper line in where on hook and off hook are at different voltages, along with the ring level.

Best advice would be, stay well away from any telecom gear.
If you send something down their lines and damage any of their gear in any way, you could get your butt sued for millions.
(and don't think for a moment they won't know where it came from)
Go play your guitars.

 

[SparkyCal]

Bridge is a 2A bridge rectifier and (as shown) is made up of 4 diodes.
I would imagine this is made for the old style copper line in where on hook and off hook are at different voltages, along with the ring level.

Best advice would be, stay well away from any telecom gear.
If you send something down their lines and damage any of their gear in any way, you could get your butt sued for millions.
(and don't think for a moment they won't know where it came from)
Go play your guitars.

Thanks Bluejets. My phone line has nothing to do with the phone company. It’s all internet based

 

[Bluejets]

If it's copper line to the house it is .
The telecom company own that and all downstream from there.
This is exactly what I was referring to when I said stay out of it. A little knowledge is dangerous.

 

[crutschow]

I would measure the on-hook and off-hook voltages of your system to see if the circuit is compatible with your MagicJack voltages.

 

[SparkyCal]

Hi. I will probably stay away from this but the magic jack system works through the internet. Not the phone co

 

[crutschow]

I will probably stay away from this but the magic jack system works through the internet

Do you mean you are giving up on the project?

The MagicJack phone output is meant to emulate the POTS signal levels of 48Vdc on-hook and about 7-12Vdc off-hook (with a 15-20mA telephone load), but I don't know how close.
That's why I suggested a measurement of those voltages.

But I see no problem with adding a circuit to detect on-hook and off-hook conditions if the impedances are high enough (probably on-hook current no more than a mA and off-hook current of a few mA, sufficient to light an LED).

(I have an Ooma internet phone, similar to the MagicJack, which works very well.)

 

[SparkyCal]

I don’t have a clue what sort of schematic to use and I don’t have enough know how to figure it out

 

[crutschow]

I don’t have a clue what sort of schematic to use and I don’t have enough know how to figure it out

I can help you with that if you can measure the MagicJack on-hook and off-hook voltages.

 

[SparkyCal]

I can help you with that if you can measure the MagicJack on-hook and off-hook voltages.

If I plug in a phone jack and put my red probe from my multimeter on the green wire and the black probe on the red wire, will that give me the on the hook reading? And then make the same measurement when a call comes. In and is picked by a phone using another jack?

 

[SparkyCal]

Would this work: you figure out how big of a resistor it would take to safely light a LED, assuming a 48 volt power supply. Then install it in line with the green wire, Presumably, when the phone is not being used, the LED is at full brightness. When on a. Call, it is dimmed?

 

[crutschow]

If I plug in a phone jack and put my red probe from my multimeter on the green wire and the black probe on the red wire, will that give me the on the hook reading?

Yes.

And then make the same measurement when a call comes. In and is picked by a phone using another jack?

You don't need a call coming in, just pick up the phone (off-hook) and measure the line voltage.

Would this work: you figure out how big of a resistor it would take to safely light a LED, assuming a 48 volt power supply.

The current would need to be small, since the phone system (MagicJack in this case) detects the 48V current to determine if the phone if off hook, indicating you want to make a call.

 

[SparkyCal]

Thank you crutschow, I will report back once I get a chance to do the measurements

 

[Externet]

Yes, very possible to implement. I did that 40+ years ago, hanged the led on the ceiling where was seen by personnel in a charity/philanthropy office that had only one telco landline and like 4 paralleled telephones to desks...
But works in reverse: When line is available (not in use), led is lit. When busy (in use), led is off.
Use a green led to denote such. If I remember, only red leds existed then. If I remember, a ~22V zener and a ~6KΩ resistor, all in series to the green led; in parallel to red/green wires.

The telco line has about 6 VDC with handset off-cradle. Voltage does not pass trough the zener and led stays off. When handset is on-cradle, voltage is like 50VDC and overcomes the zener, turning the led on.
I think I did not even use a polarity steering bridge, just checked the +/- before connecting the contraption. Cannot even remember if I did something to protect the led from the ringing signal. Probably not and worked fine years and years...

And I did not care about the telco, nothing was injected to risk their circuits.

 

[Audioguru]

A phone that is on-hook draws zero DC current. The green LED in the Circuits-Today circuit draws possibly enough current for the system to be off-hook all the time. Then use a battery or isolated power supply to light the LED and hope that the base bias current for the transistor is low enough not to be detected as off-hook.

 

[SparkyCal]

Hmmm. I tested the line with my multimeter. When it was on the hook, I got a reading of -50.1 v DC. when it was off the hook, it is -5.1 DC. Note that these are negative readings.

 

[crutschow]

Hmmm. I tested the line with my multimeter. When it was on the hook, I got a reading of -50.1 v DC. when it was off the hook, it is -5.1 DC. Note that these are negative readings.

Just reverse the meter leads to get a positive reading.
How did you differentiate the line connection polarity?

Now you can try connecting a LED with a resistor in series across the line when on-hook to see how much it drops the voltage (you likely don't want the voltage to drop to less than 40V).
I calculate the internal impedance of the MagicJack to be about 2.25kΩ, based on a nominal 20mA off-hook draw from the phone.

Start with about 50kΩ in series with the LED (use a high brightness type).
It that's not bright enough you can try reducing the resistor value.

 

[SparkyCal]

Thanks for your help. It worked. I used a 47K resistor and a blue LED. When the line is not in use, the LED is bright. When it is in use, it dims.

It would be better if it were the other way around, but it still works and is useful.

 

[crutschow]

When the line is not in use, the LED is bright. When it is in use, it dims.

If you put a 10v to 20V Zener diode in series with the LED, it should turn off completely off when the phone is off-hook.