NB - potentially unreliable due to arduino timings, buyer beware!
Code to read output from chartplotter (NMEA DPT sentence)
Then parse out depth
Convert to 7 segments etc
Then write out to NASA Depth Repeater
I2C bit banging and 7 segment code from modified from Peter Holtermann
See... http://wiki.openseamap.org/wiki/De:NASA_Clipper_Range
white lead - SDA
red lead - SCL