Serial Port Opto-Isolator

Using an Optical Isolator on the serial cable between a WeatherMAX/WeatherLogger and a PC


The serial port connection on a personal computer contains a poor connection to earth ground. Many factors can cause a difference in electrical voltage between the ground of the serial port and the ground of a mast. If the voltage difference is large enough then it can discharge through the instrument and computer causing one or both to latch-up or fail.

The least expensive way to avoid this potential problem is to disconnect the serial port cable when static producing storms are in your area.

However, if you want to monitor the weather in real time during storms, you need to leave the serial cable connected. In this situation, you can use an optical isolator to break the ground connection between the instrument and computer.

A recommended isolator

Optical isolators for RS-232 ports are available from a few different manufacturers. We have tested a unit manufactured by B & B Electronics that is an excellent unit at a very good price. As of 12/97, the price for the isolator and the required power supplies is less than $90.00.

You can order the units from the manufacturer.

B & B Electronics Manufacturing Company

707 Dayton Road
PO Box 1040
Ottawa IL 61350 
Tel: (815) 433-5100
Fax: (815) 434-7094

The isolator is Model 232OP4 and it requires two Model 232PS power supplies.

Cables needed to use the 232OP4 with a WeatherMAX/WeatherLogger

You need to use a null modem cable (or a modem cable and a null modem adapter) between the PC and the isolator. You also need to use a DB-25 Male to Female null modem adapter with the WeatherMAX/WeatherLogger serial cable.

Please refer to the following diagram:

2320P4 Cable Configuration


2320P4 Cable Configuration

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