Has anyone successfully managed to control the output of standard messages of a GPS EM406A (http://www.futurlec.com.au/GPS/EM-406A.jsp) from Futurlec? I'd like to stop the GSV satellite data from being sent every 5 seconds as it interferes with the timing of the RMC messages sent every second. I have attempted to send a message described in section D of the NMEA Input Commands described in the above data sheet.
I first tried to simply send the characters "$PSRF103,03,00,00,01*27" using the serial terminal send window but it had no effect on the GPS module. When I looked at the waveform of the characters received by the module using a Saleae Logic probe, the characters appeared to be OK except for the long inter character pause that presumably the terminal window inserts. In case, this was causing a problem for the GPS module, I programmed an 08M2 chip to simply sertxd (" $PSRF103,03,00,00,01*27 ") and then connected pin0 to the GPS module. Again the logic probe appeared to show a clear signal being received by the GPS module (this time without the long pauses between characters) but again there was no effect on the sending of the unwanted GSV messages.
I have double checked that the checksum (27) is correct and am confident that it is.
The connection to both the RX & TX terminals of the GPS module is via 2 NPN transistors which simply inverts (and voltage converts in the case of the PC) the waveform from the 08M2. The transistor inversion circuit for the RX pin of the GPS module simply consists of a 10kohm resistor between the PC/08M2 output and the NPN transistor base and a 1kohm resistor connected between the collector and 5 volt battery (4 Ni-MH AA cells). The emitter was connected to earth. I connected the logic probe to the collector of the NPN transistor which also connects to the GPS module. The GPS module is powered by the same 5 volt battery.
I've googled looking for other peoples experience with this but the only references that I've found are from people using specific hardware and propriety software and they don't seem to have had any problems. They don't mention any other specific requirements from those mentioned in the data sheet.
I also don't see any sign of a 1Hz signal coming from pin6. I've tried pulling up the pin using a 10kohm resistor in case it is open collector output but still don't see any signal. I don't particularly want this signal but it just appears to be another area where the datasheet doesn't seem to correspond with the module's performance. The TX messages appear to work exactly as described and have been successfully received by both the terminal window and a 20X2.
I'm somewhat at a loss as to what to try next.
I first tried to simply send the characters "$PSRF103,03,00,00,01*27" using the serial terminal send window but it had no effect on the GPS module. When I looked at the waveform of the characters received by the module using a Saleae Logic probe, the characters appeared to be OK except for the long inter character pause that presumably the terminal window inserts. In case, this was causing a problem for the GPS module, I programmed an 08M2 chip to simply sertxd (" $PSRF103,03,00,00,01*27 ") and then connected pin0 to the GPS module. Again the logic probe appeared to show a clear signal being received by the GPS module (this time without the long pauses between characters) but again there was no effect on the sending of the unwanted GSV messages.
I have double checked that the checksum (27) is correct and am confident that it is.
The connection to both the RX & TX terminals of the GPS module is via 2 NPN transistors which simply inverts (and voltage converts in the case of the PC) the waveform from the 08M2. The transistor inversion circuit for the RX pin of the GPS module simply consists of a 10kohm resistor between the PC/08M2 output and the NPN transistor base and a 1kohm resistor connected between the collector and 5 volt battery (4 Ni-MH AA cells). The emitter was connected to earth. I connected the logic probe to the collector of the NPN transistor which also connects to the GPS module. The GPS module is powered by the same 5 volt battery.
I've googled looking for other peoples experience with this but the only references that I've found are from people using specific hardware and propriety software and they don't seem to have had any problems. They don't mention any other specific requirements from those mentioned in the data sheet.
I also don't see any sign of a 1Hz signal coming from pin6. I've tried pulling up the pin using a 10kohm resistor in case it is open collector output but still don't see any signal. I don't particularly want this signal but it just appears to be another area where the datasheet doesn't seem to correspond with the module's performance. The TX messages appear to work exactly as described and have been successfully received by both the terminal window and a 20X2.
I'm somewhat at a loss as to what to try next.