LPT Interface

This LPT interface is intended for use with N1MM Logger for CW and voice .wav files. It receives LPT CW data on pin 17 and keys a simple garden variety NPN switching transistor (like a 2N2222A) which in turn is connected to the CW port of the transceiver. This is set up for positive polarity keying (most modern rigs) and not for grid block keying. This is schematically represented by the green circuit below. This circuit receives PTT data on 16 of the LPT port (for both CW and SSB) and keys a similar circuit to activate the PTT circuit in the transceiver. This is represented by the red circuit below. For my interfaces, I use a small piece of perf board (available from Radio Shack) and install the circuit in a Radio Shack metalized plastic 25 pin male LPT connector. The board fits nicely between the solder tubs on the wiring side of the connector. I also add an RF choke to the lines just to ensure there will be no stray RF pickup.