Phone line status indicator

[RODALCO]

Phone line status indicator

This simple circuit comes in very handy to check wheater a phone line is free, engaged or receiving a ring signal.
I used to service and install remotely read Time of use kWh meters all over the place which were read by cellphone or landline.
The reason I designed it was that after the installation a reading check was carried out and I was waiting for the meter to be read and never was sure if anything was in progress.
As you already know is that a phone line has a standard no load voltage of around 50 Volts DC.
So to set up the circuit the VU meter needs to read about ¾ schale.
R1 requires a value of around 400 Kilo ohms ¼ Watts. You may have to experiment with different values between 270 and 470 k ohms. as movements vary between 100 and 250 µA.
The bridge rectifier is to avoid having to swap the phone wires over in case the polarity is the other way around.
How it works. If the line is engaged the voltage is about 8 volts dc and the meter will give a low reading. If the ring signal is present it will give a high reading (ring voltage around 90 volts ac). and the no load voltage will give a ¾ schale reading.
I have 3 of these meters connected permanently to my phoneline at home and the loading on the phoneline is negligible.
One near the computer, the other two built in standard house phones.
It comes in very handy to see if the line is engaged to the internet while in the other part of the house.

 

[Analog]

Would a circuit like this affect a DSL connection?

 

[mramos1]

Would a circuit like this affect a DSL connection?

With DSL in the US. They give you line spliters that break off the DSL and the DC/phone side. So if you use the spliter here (in the US) it would not be a problem.

 

[RODALCO]

Don't see any problems.
The circuit draws in standby mode at 50 Volts dc 125µA with the 400 k ohms series resisitor.
Most houses have more than one phone in parrallel with each other which imposes a far larger burden on the phoneline which is in the mA's capacitive through the phones circuitery anyway.

If on a landline for the internet like I am, I use a contactor changeover switch as soon as my computer goes on line. It increases my modemspeed from 28kB/sec to 50.2 or 52 kB/sec.
The contactor basically drops all the phones completely off the phone line.
The meter still remains on my computer connection as status indicator.