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GPS City Q&A » Marine Network » Why and for what is 3 k ohm resistor needed?

Marine Network (3 replies)

Item

Original Question

Why and for what is 3 k ohm resistor needed?

› Lowrance NMEA 0183 Adapter Cable

Author

Reply

Martin
Copenhagen

Original question asked on Dec 22, 2011, 12:06pm

In series with the tramsmit wire are mounted a 3 k ohm resistor, and the transmit wire is connected to the cathode of a 4148 diode. The anode are connected to ground.
Why and for what is that needed?

Jordan
GPS City

Reply #1 on Dec 22, 2011, 1:26pm

The resistor and Diode is to control the voltage level for non RS232 based NMEA 0183 devices. If your device needs true RS232 voltage levels you can cut the resistor and diode out. Before doing so you may want to contact Lowrance and the maker of the other device to make sure if cutting it off for that set up is needed

Martin
Copenhagen

Reply #2 on Dec 23, 2011, 2:36am

Thanks! I suppose the resistor is doing the voltage limitation. How many listeners( max current in mA) can be connected to the tramsmit output? Do you know what the minimum "1" voltage for NMEA is?

Jordan
GPS City

Reply #3 on Dec 27, 2011, 12:53pm

They do not specify the current draw or the max number of devices listening to the one NMEA output. I have attached three devices to one NMEA transmitting line on a similar device in the past. I am sure you can do more.

Just be careful when hooking up multiple devices that you do not get data collision by hooking two transmitting devices to the same receive line without special circuitry to manage the transmission. Multiple listeners on one transmit line is normally fine. But every device is different.

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