Thanks for that, Dennis.
I have not tried to output to the ST60 Multi - one thing at a time. The +
input from the Multi is connected to pin 2 and the - input from the Multi is
connected to pin 5.
I will try shorting out the pins you suggest

Phil


"Dennis Pogson" wrote in message
...
Phil Stanton wrote:
Can anyone help
I have a Raymarine ST60 Multi and want to get NMEA data (Wind &
Depth) into the 9 pin serial port on my laptop. If the laptop is not
connected to anything at all (including power supplies) this works
fine. If I connect it to the boats 12v supply via a cigarette type
laptop power supply, or an inverter using the normal laptop power
lead I get nothing.
Equally if I connect the USB port via a Serial to USB lead to the GPS
and AIS input I immediately loose the NMEA input.
I have been told I need to use an optocoupler (optical isolator) and
have bought a 4N25 chip.
Can anyone suggest what the problem is and / or give me a circuit
diagram of how to use this optocoupler

many thanks

Phil

You don't say whether you have grounded the nmea output to pin 5, but I
have
found that if you don't do this you get no signal, even when pins 2 &3 are
receiving/transmitting. On really old laptpos/PC's we used to also short
out
pins 4 & 6, plus 7 & 8, to prevent the laptop thinking it was connected to
a
modem with buffering protocol, no longer necessary.

Dennis.