Hello Babar,

The transformer that I mentioned in previous postings is used to go Offhook when connected to Line in parallel. to go Onhook just disconnect the transformer. A relay can be used to connect the transformer.

Directly connecting an isolation transformer to telephone line for the purpose of placing load (to go off-hook) is not the correct method. The iron core of transformer will saturate with the loop current, unless you have a wet transformer.

I recommend to place a resistor accross TIP and RING in order to go off-hook. The transformer must be ac coupled, what it is meant for. Use 0.1uF/250V capacitor in series with the transformer when connecting it to telephone line.
Use the relay to connect a resistor (of suitable value which draws at least 10mA from line in order to insure that TELCO detects it as off-hook)


Regards

IA