check out rat ring its a PIC to telco interface Jinx wrote: Looking around, I find a variety of phone line interfaces. Some are for simple ring detection, others are for analogue signals. I'd like to know if the circuit attached will do what I hope it will, and also what components (protection, isolation, steering etc) may need to be added For compliance, because there's a mains-powered PIC-based circuit, I believe a transformer would be mandatory. Most of the projects I found on the web use resistors or optos, often with zeners/caps/diodes. They are generally powered by line voltage. Many have a few hundred pF at various positions across the line. There seems to be no concensus about that The rectified HVAC ring voltage is detected by the PIC, which then turns on the relay for the LV analogue voltage. I figure this is the equivalent of the hook switch. The incoming signal is buffered, the outgoing is driven Should I wait for a ring pause (ie no AC) before engaging the relay, to protect the analogue side from ring voltage, or does the exchange stop that voltage as soon as the relay is engaged ? Any other gotchas to be aware of ? TIA ================================= For a successful technology, reality must take precedence over public relations, for nature cannot be fooled -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist --------------------------------- Be a better sports nut! Let your teams follow you with Yahoo Mobile. Try it now. -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist