Digital/Standard Phone Line Tester

It appears that you are using AdBlocking software. The cost of running this website is covered by advertisements. If you like it please feel free to a small amount of money to secure the future of this website.

Radio Shack sells a similar device without the high current function. It detects one or two lines on an RJ-11 and tells you its polarity.

The schematic is:

                 |          | 
                 \          | 
         Line 1  /680      \ / red/green LED 
                 \ .5W     --- 
                 |          | 

The circuit for Line 2 is identical. Note that each red/green LED comes standard as reverse wired (red LED “forward”, green LED “reversed).

Based on the above, I think an appropriate modification to include a high current indicator would be: (I’ve tested it)

           |         |           |          | 
           |         |           \         --- 
           +--->|----+           /         / \  red/green LED 
            red/green            \ 680      | 
              LED                | .5W      | 

You can adjust the 20ohm resistor value to set what is considered “high current”. 20ohms lights the LED at around 90ma.


  • Dan Ts’o



© 1998-2019 – Nicola Asuni - - All rights reserved.
about - disclaimer - privacy