Eight tips aid USB use

Here are eight tips on successfully using a USB-Serial convertor for data acquisition on a Windows computer.

Many measurement devices can send data to a computer over RS232 links.

As USB ports have largely replaced RS232 ports on new computers, people are increasingly using USB-Serial convertors to access data from their instruments.

The convertors are simple to use but sometimes need careful setting up if they are to work properly.

Here are eight tips on successfully using a USB-Serial convertor for data acquisition on a Windows computer.

1: When you install a USB-Serial convertor, Windows will assign it a COM port.

Check this by opening Windows Control Panel and choosing first System, then Device Manager, then Ports.

It will look something like "USB serial port(Com X)", where X is the COM port number assigned.

A question mark indicates that there is a problem with the drivers or the connection.

2: You may find that Windows assigns your convertor a COM port number that is higher than your software can handle.

If so, use Device Manager to reassign the COM port to a lower number.

Select your convertor and click Properties.

Choose Port Settings, then Advanced.

Make a note of this number and the other settings listed.

You will need to enter them in your data acquisition software.

3: Windows may list all the lower COM port numbers as being in use.

This is not always so.

Look at the computer's actual COM ports physically available and you may find a lower port number.

4: If your USB-Serial device is "designed for Windows" then it will have a serial number.

Windows reads this and uses it to remember which driver and COM port number to use for that device.

This means that when you unplug the convertor, Windows continues to consider its COM port number in use and you can't then plug another device or convertor into that COM port.

If necessary use Control Panel's Device Manager to over-ride this COM port setting.

5: When using a USB-Serial convertor, you need to make sure that it is providing data in the way expected by your data acquisition software.

The serial settings must be the same.

To find out the communication settings use Device Manager.

6: If you have set your data acquisition software to continually acquire data you must make sure that your USB-to-Serial convertor is continually providing data and not buffering it.

How you do this depends on your convertor.

For an Edgeport convertor, for example, you need to use its utility program to set its ports for "low latency" and "fast read and writes".

7: From the computer's perspective, the adapter is an active USB device.

What this means is that it will only be available, or listed as an option, if it's plugged in.

8: To download free data acquisition software to collect data from RS232 instruments go to the Windmill Software website.

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