Pixhawk GPS port supply voltage higher than GPS module limit

[wcfung1 (Frankie Fung)]

When I measured the voltage across the Vcc and ground pin of the GPS port in Pixhawk, it reads 4.5V and above.

However, the data sheet of uBlox M8N GPS says supply voltage is 2.7 - 3.6V (see attached).And this GPS module has been connected to the above port for few years.

How can the GPS module survive the over-voltage without burning ?

Thank you.

[hassani (MSadegh Hassani)]

Hi,
There is likely to be a voltage regulator inside the GPS module to reduce the voltage.

[Mustafa_Gokce]

Which GPS module are you using? If it is the one provided with the Pixhawk, no issues.

[wcfung1 (Frankie Fung)]

The GPS module is separately sourced, not supplied with Pixhawk.

At the second thought, I think I am mistaken initially, as you can see from the attached screen shot from ardupilot

showing the GPS port pin voltage.

The 3.3 V I referred earlier is for the Tx and Rx pin, while the voltage across the Vcc and ground pin I obtained from a multimeter is 4.5V and above (depending I power the Pixhawk using USB or flight battery), in kline with the 5V as shown in the attached diagram.

[wcfung1 (Frankie Fung)]

At the second thought, I think I am mistaken initially, as you can see from the attached screen shot from ardupilot

showing the GPS port pin voltage.

The 3.3 V I referred earlier is for the Tx and Rx pin, while the voltage across the Vcc and ground pin I obtained from a multimeter is 4.5V and above (depending I power the Pixhawk using USB or flight battery), in line with the 5V as shown in the attached diagram.

[xfacta (Shawn)]

The other issue with GPS supply voltages that a lot of people miss, is:
Although the GPS electronics actually run off 3.3v (in most cases) the expected supply voltage is 5.0v and there is some sort of crude regulator.
I say “crude” because
a) there’s very limited board space
b) supply voltages below 5.0v start to affect actual GPS performance

@tridge

with some flight controllers running at around 4.8V. I found the F9P based modules did quite badly and after looking into possible causes I found that by ensuring all flight controllers had at least 5V the performance was a lot better. If you have a F9P GPS then be sure to check your power. You can see the board voltage in most boards by looking at the POWR.Vcc messages in onboard logs or in the POWER_STATUS mavlink message in your ground station. If you are dipping below 5V then it would be worth fixing your power setup.

And consider that is with new GPS modules. Good luck with the older ones and a poor power-brick!
Or cheap copies…

And consider the 4.7v supply (meant to be about 5.2v) from a cheap power brick goes through at least 1 connector to get to the flight controller, probably two connectors, then another two connectors from the flight controller to the GPS unit. Add in the resistance of those connectors, some noise and ripple, it’s a wonder the poor GPS units work at all.