The specs are impressive for a cheap little unit. It can track up to 22 satellites on 50 channels and "achieves the industry’s highest level of sensitivity i.e. -161 dB tracking", while consuming only 45mA supply current.
The sensitivity claim is questionable, at least with the terrible little antennas that mine came with. I have an ancient Trimble antenna laying around with an MCX connector. When I got an MCX to U.FL pigtail and connected this to the NEO-6M, I got much better results, even getting lock indoors.
So I ordered a handful - 5 of them to be exact. My units have places for 5 wires:
When it is powered up, it begins chattering away without any need for initialization or provocation, sending out NMEA sentences. It sends them at 9600 baud. This is nice. It is useful without diving into some manual trying to figure out how to get it initialized.
Mine seems to run fine given 3.3 volts power (which I get from the CP2102 USB to serial dongle I have it wired to). You can give it 5 volt power. One listing says to give it from 3 to 5 volts. It has a 3.3 volt LDO regulator (see the schematic). The datasheet says that it will run on 2.7 to 3.6 volts, so most likely given 3.3 volts the LDO regulator is giving it 3.0 volts or so. Rx and Tx are at 3.3 volt logic levels, or so it seems. Allegedly the pins are 5 volt tolerant. Whatever the case, it is working fine connected to my CP2102 dongle.
My little board has an LED and it isn't just to indicate power. When the light is on solid, it means it ain't got no lock. Once it starts blinking at 1 Hz, the unit has lock.
It also has a HK24C32 two wire serial EEPROM (4K) to hold information when it is powered off (up to 2 weeks) along with a battery. This is supposed to help it more quickly get its first fix (TTFF).
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