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HAICOM HI-303III GPS
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I was given this item which is strictly a receiver and has no display. It is designed to
be connected to a PDA or a computer in order to make use of it. It can be connected to
a compact flash connector or with a serial RS232 connection. I used the RS232.
The cable is quite simple except that the GPS uses a mini-1394 connector which are not too common or easy to find. I found them quite cheaply in my travels in China and I built the cable with a DB9 connector for the computer. It is probable that the TXD wire to pin 3 of the DB9 connector is not necessary because, as far as I know, the GPS receiver transmits information but does not receive anything. Still, it is easy to connect anyway. The GPS receiver requires 3.3 V power supply and I get it from a USB connector by dropping down the USB 5 V with a couple of diodes. It uses up a USB port of which I have plenty but I might make a short USB extension cable from which I could get the power supply for the GPS and still plug the mouse into the same USB port. 
First I did some basic testing by connecting the GPS receiver to the serial port. I used Hyper Terminal, configured at 4800 baud, and confirmed the computer receives NMEA-0183 sentences. The GPS sends and the computer receives $GPRMC, $GPGGA, $GPGSA, GPGSV and other sentences which contain information about position, speed, etc. I then installed Haicom's Viewer software and it does display position, speed, direction and other information but it is only a basic program which has no map or graphic capability. Google Earth also has a limited capability. It will receive the GPS data and center the map on that point but it does not allow changing the scale (height of view) or displaying any other data like speed, etc. I have not really used it in any mobile application yet. |
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NMEA-0183
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NMEA-0183 Serial Configuration (data link layer) Baud Rate: 4800 Data Bits: 8 Parity: None Stop Bits: 1 (or more) Handshake: None Application Layer Protocol Rules Each message starting character is a dollar sign. The next first five characters identify the type of message (talker). All data fields that follow are comma-delimited. The first character that immediately follows the last data field character is an asterisk. The asterisk is immediately followed by a two-digit checksum representing a hex number. The checksum is the Exclusive OR of all characters between the '$' and '*'. According to the official specification, the checksum is optional for most data sentences, but is compulsory for RMA, RMB, and RMC (among others). <CR><LF> ends the message
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