I have a GPS-RTK2 Board - ZED-F9P (Qwiic) (GPS-15136) connected to a Raspberry Pi via USB. This means that the Pi is supplying power to the RTK board. I’m concerned that if I connect other USB devices to the Pi, it may not always be able to supply enough power, so I’d like to run the RTK from a USB charger and create a separate data connection to the Pi. The USB port would only be used to supply power.
I’ve tried using an I2C connection via the Quiic socket, connecting the wires to the GPIO pins of the Pi. However, I found that this only works if you connect all four wires including the power and ground. If I do that, the RTK board takes power from the Pi via that channel, so I’m back where I started.
Is there an easy way to create a data channel from the Pi to the RTK board that does not also supply power? Preferably without having to solder extra components onto the board?
Alternatively, would it be safe to connect all four wires of the Quiic connector as well as providing a powered USB connection, or would that risk an overload?
Hi simon.
I’d recommend applying power through the USB connector from your external power source and then connecting the Qwiic connector to your Pi. As long as the Pi is turned on before and shut off after the GPS, you’re OK and don’t need to worry about power back feeding from the GPS into the Pi. If you’re concerned you might accidentally power the GPS before or after the Pi, cutting the red 3.3 volt wire on your Qwiic cable will isolate power between the Pi and the GPS.
Thank you. Both of those suggestions worked. Using i2cdetect on the pi (i2cdetect -y 1) I can see that the RTK board is on I2C port 42. Now I just need to write a bit of software to read the data.
The second suggestion is the better one, as I just want to be able to turn the system on and leave it. I don’t want to have to remember the right order to plug in the USB cables. Also it works when the RTK board is plugged into the pi’s USB, which is useful during testing - the pi should be able to read RTCM messages from the I2C interface and from the USB.
By the way, I suggest that you add a section to the hookup guide about connecting to a pi andto an Arduino using the qwiik connector. Finding the correct cable, figuring out which port does what, finding the pin layout on the pi and getting this question answered all involved a bit of work. Also the guide doesn’t mention that you can power the board via the qwiik channel.