9-pin null modem cable
Nullmodem Cable, 9 to 9 Pin Female D-SUB
1 - Carrier Detect
2 - Receive Data
3 - Transmit Data
4 - Data Terminal Ready
5 - System Ground
6 - Data Set Ready
7 - Request to Send
8 - Clear to Send
Pins 6 &1 are wired together to simulate 'on-line' status. This Nullmodem configuration is also for gameply like Westwood's Command & Conquerer "Tiberian Sun".
1133 22 August 2007
The telephone ring generator shown below generates the needed high voltage from a simple switching mode power supply.
The circuit presented here can be used for connecting two telephones in parallel and also as a 2-line intercom.
Circuit to illuminate an LED when any phone extension is off-hook. LED should illuminate when circuit is off-hook.