SparkFun Forums

[Calebcohoon]

Hello all,

I'm currently working on a simple GPS project using a EM-406 module that displays the Latitude and Longitude to a LCD screen. I'm using a 8052 microcontroller for parsing the NMEA data. The strange problem I'm having is that when the GPS module is connected to the microcontroller and LCD circuit the module can never get a fix but, when the module is the only thing connected to power it gets a fix fast. I'm not an expert at electronics but could there be a noise problem? If there is what could I use to clean up the noise so everything works together? Any help would be appreciated. Thank you, Caleb

[leon_heller]

A harmonic of your 8052 oscillator might be swamping the GPS signal. I'd check multiples of the clock frequency and try a different crystal if it looks like that is the problem.

Leon

[Calebcohoon]

Hmmm, I never thought about that maybe the crystal could be causing a problem...? I was thinking maybe the LCD or something was causing too many spikes in the voltage line. When I turn on the module all by itself with nothing else running it fixes fine and then when I connect the microcontroller to power the module stills stays fixed, and then finally when I turn the LCD on the fix get losts. Is there anything I could connect to the LCD to help? Maybe some capacitors? Here's a pic of the circuit:



Thanks again! Caleb

[leon_heller]

One of those long leads could possibly be acting as an antenna and re-radiating a signal. The GPS signal is quite weak and it wouldn't take much to interfere with it. Using one of those solderless breadboards is asking for trouble, I'd put everything on a PCB.

Leon

[ohararp]

Leon, I am interested in the em406. Just wondered how things were coming along and your impressions of this device?

[leon_heller]

Leon, I am interested in the em406. Just wondered how things were coming along and your impressions of this device?

It's the OP who is using it, not I. I'm using a u-blox LEA-4A, which works fine with a 16F88 on a PCB I designed.

Leon

[ohararp]

Caleb, I have moved past the breadboard and have successfully integrate the EM406 into a pcb design. By implementing a large ground plane I am now able to get a lock in some crazy places where I wouldn't have dreamed getting a lock with the lassen iq or the em406 on a breadboard. Check out http://www.sparkfun.com/cgi-bin/phpbb/v ... 5158#15158 for more details.

[Calebcohoon]

Hey ohararp!

Thanks for the update on your project and the tip on using a large ground plane. That's great you got it to work well for you. My project is still on a bread board. Hopefully, I'll move it to a PCB someday when I have the money (or interest)! Later, Caleb

[ohararp]

FYI...I unknowingly passed the USB (5V) copper trace on the bottom of the pcb directly under the EM406 connector and find that when the USB line is plugged into the board the NMEA sentence/RS232 comm gets garbled. One of those unforeseen issues that cropped up...