ELEKTOR FORUMS

GPS Receiver on USB -- FAQ (frequently asked questions)
Elektor Electronics June 2005

By Paul Goossens, Elektor Electronics labs

www.elektor-electronics.co.uk

Q1. What operating systems are suitable for the USB GPS module?
The chip manufacturer only supplies driver programs for:
- Windows XP
- Windows 2000
- Windows ME
- Windows 98
- Linux
- MAC OS-X
- MAC OS-9
- MAC OS-8
- Windows CE (on request only)

The programs Lassen-iQ and iQ-chat are only available as Windows programs. Users of other operating systems will have to make their own arrangements for the module to switch from the TSIP protocol to NMEA.

Q2. Can I use the module with a PDA?
In principle, yes, but you will require a driver program for the USB-GPS chip. So far, the manufacturer only supplies drivers for Windows CE and Linux. These are available on request from FTDI.
If the PDA employs Windows CE or Linux, and has a USB port, then the module can be connected to the PDA.
See also Q1.

Q3. I have built the module and it all works. What software do I need?
It all depends on what you want to do with it. The most obvious application is a navigation system, for which several programs are available. The following applications have been tested in the Elektor abs: Route 66 and Microsoft Autoroute. The latter is included in MS-Works which often comes pre-installed on new PCs and laptops.

If you would like to experiment with GPS, the software on the CD-ROM may be useful. The Internet is also a good source for alternative, free, software, for example, visualGPS (www.visualgps.net)

See also Question 8.

Q4. Where can I find further information on the USB-GPS chip?
The FT232M (IC1 in the circuit diagram) is manufactured by FTDI. Detailed information may be found a www.ftdichip.com

Q5. The circuit diagram shows an LM117-3.3 in position IC2, however the parts lists states LM1117-3.3. Which is correct?
IC2 should be a type LM1117-3.3. The identifier in the circuit diagram has one ‘1’ missing.

Q6. Windows recognizes the module as ‘Microsoft Ballpoint’.
If the module is programmed to transmit data using the NMEA protocol it may be recognized as a ‘Microsoft ballpoint’ by the Windows operating system. The confusion is caused by the certain combinations of characters in NMEA coded strings that happen to be recognised by Windows as the identifier for the Microsoft Ballpoint.

As soon as this happens, it is no longer possible to open the relevant COM port. Also, from that moment on the cursor will leap across the screen in random fashion. The problem is easy to solve.

First disconnect the GPS module, enabling the mouse to function normally again. In Windows, go to Device Manager. This is easiest done by right-clicking on the My Computer symbol and then selecting Properties from the menu. In the new window, open the Hardware tab, then click on Device Manager.

The window will show a list of hardware devices inside your computer. Click on Mouse to view all installed devices (usually only one mouse). Now reconnect the GPS module. After a few seconds, a second mouse will appear in the window identified as ‘Microsoft Serial Ballpoint’. As soon as that happens, disconnect the module so you can use the real mouse again. Depending on your PC the second mouse will remain visible in the window for a few seconds. Right-click on its symbol, then select Properties. In the screen that pops up, you can opt not to use this device by ticking ‘Disable in current profile’. Click on OK and close all other windows.

The next time you connect the module again it may happen that the Serial BallPoint is recognized again, but Windows will not actually attempt to use it. From then on the GPS module will work as intended.

7. My PC can only access COM1 and COM2. How can I make the module appear at one of these?
Most PCs have at least two serial ports, identified by Windows as COM1, COM2, etc. The GPS module when installed will ‘grab’ the next available free COM port. Fortunately, Windows does allow COM ports to be renumbered.

Go to the Windows Device Manager and select the first serial port (COM1). Right-click on its symbol. Select Properties, in the window that pops up, click on Advanced.

In the new window, you will see the text ‘COM port number’, followed by a list, with ‘COM1’ highlighted. Change this setting by selecting a different (higher) COM number. This change will take effect the next time you start Windows.

If at this point you connect the GPS module it will appear under ’COM1’. In a few cases, the above workaround may not be sufficient to solve the problem. Assuming your GPS module has been assigned to COM7, go back to Device Manager and select COM7. Again open Properties and then Advanced. In the new window redirect this port to COM1. Disconnect the module and wait a few seconds. Connect it again and hey presto, the GPS module appears under COM1.

Q8. What software is supplied with the kit from Elektor?
The CD-ROM supplied with the kit of parts (order code 040264-71) contains:
- a pdf reprint of the magazine article
- Windows USB drivers
- Lassen iQ-chat (simple program to communicate with the GPS module)
- Lassen iQ-monitor (graphic tool to trace the operation of the GPS module)
- Reference manual for the GPS module (pdf file)
- An example program in Visual BSIC to explore the main features of the GPS module.

Q9. Why is only one of the two ports in the GPS module used?
Our interface employs only one port. We set out to keep the design as simple as possible, enabling readers with little or no experience in practical electronics to successfully complete this ambitious project. By keeping the number of ports down to just one, we prevent confusion in this group of users.

Another reason was to make sure the interface remained compatible with a previous version of the GPS module, the Lassen-sQ. During the design phase, the newer Lassen-iQ module was not yet available in volume quantities nor did we know its final price.

A second port may be useful in combination with, for example, DGPS. However we believe a limited number of people have DGPS receivers. The second port should not be too difficult to make available; simply add, say, a MAX232 chip. All relevant information on this extension may be found in the Trimble reference manual.

Q10. My module does not work, all I get in HyperTerminal is random characters.
Your GPS module is probably functioning just fine. Port 1 is probably outputting TSIP formatted data instead of NMEA. Simply change the setting as detailed in the magazine article.

Q11. Everything seems to work just fine, except iQ-monitor
This is normal. If your navigation program s working properly in combination with the GPS module, port 1 is programmed to supply NMEA data as required. The Lassen-iQ utility is the only program intended to work with the TSIP protocol only. If you want to use the iQ-monitor, you have to change the port-1 output format from TSIP to NMEA, and the utility will work as properly. Do not forget to revert to NMEA again, else your navigation software will no longer find the GPS module!

Q12. What’s included in the kit supplied by Elektor Electronics?
The kit (order code 040264-71) contains:
- All electronic parts required, except IC3, which is not required for normal use)
- The ready-made printed circuit board
- The GPS module
- Connection piece to connect GPS module to antenna
- Antenna with magnetic sole and built-in RF preamplifier. Connection cable with a length of 5 m!
- CD-ROM with various software, Elektor Electronics magazine article, etc. (see also Q8)

Q13. Where can I buy the GPS module, FT232BM chip, etc. as individual parts?
The project is supplied as a kit for the convenience of our readers and in order to avoid component sourcing problems. The FT232BM chip and the GPS module may be hard, if not impossible, to obtain as one-off components from local suppliers. We were unable to identify retailers willing to support our project with one-off parts for readers across the globe.
Also, the price of the kit we supply is lower than the sum of all individual components obtained as one-offs, locally or by mail order.

Q14. I would like to embed the GPS interface in my own program. But how?
The CD-ROM supplied with the kit (but also available separately) contains an example program showing how your current position may be determined using the GPS module. The example is written in VB and of a clear construction, so migrating it to another programming language should not present too much difficulty.