hello, I would like to use the EM-406 GPS with an mbed. According to the GPS data sheet (http://www.sparkfun.com/datasheets/GPS/EM-406A_User_Manual.PDF), the power input ranges from 4.5V to 6.5V DC. When I power the GPS with a battery (whitout the RX/TX lines connected), the position fix indicator is set after few seconds (in outdoor). However when I try to power the GPS from the mbed's 5V output I systematically loose the position fix. Any suggestion?

Thanks in advance!

I have not use this EM-406 GPS , and I dont know if this will help you. But check current consumption for your module. Sometimes you cannot just power external device from mbed board. Stable voltage is very important to get fix for most GPS modules on a market. I know that some modules in a moment that try to get fix drain a lot of current in a pike. So this can produce voltage drops.

Thanks Piotr, for the idea. I've monitored the the power output with an oscilloscope but couldn't detect any pike. I've tried other GPS modules (Locosys LS20031 and LS20126) but ended up with the same result.

Another interesting point is that if I power the GPS unit with an external battery I get the position fix within seconds, but if I connected the GPS' ground to the mbed's ground, the position fix is lost as soon as I turn the mbed ON.

Did someone experienced this? Anyone managed to connect a GPS to the mbed without loosing the position fix? Thanks in advance.

I have had a similar experiance and eventually fixed it by shutting down the Ethernet controller, i.e. calling the function

    PHY_PowerDown();

at the beginning. As for this function, following URL would help:

http://mbed.org/cookbook/Power-Management

Hiroshi

Problem may be RF interference from the mbed or ethernet controller. Note that GPS signals are very weak and may be lost in RF noise from a source like a processor running at a high clockspeed. You could try shielding the board by enclosing it in a metal box. Still need to filter the powerlines when connecting the GPS receiver to the same powersupply.

Also the mbed has no real 5V power supply, you simply get your USB power on that pin. So you can try if that works without mbed, if that doesnt work it certainly wont work with mbed. In general you are probably off best by giving it a seperate LDO power supply.

Hi All, Thank you so much for your answers, I will test that when I return to office. Have a nice end of year holidays!

Thanks all for your suggestions! The solution proposed by Yamaguchi san could solve the problem! Now I can connect the GPS directly to the VOUT pin of the mbed and have a position fix after few minutes. I wonder if there is a simple method to put in evidence this interference noise from the mbed or ethernet controller?