October 14th, 2019

Building A 4G, GPS And Magnetic Data Logger Case

in progress

Hi There!

I recently had to create a little case to log 4G data (mainly signal strength), GPS data (fix, number of sattelites, ...) and Magnetic data (to ensure magnetic interferences are kept to a minimum), in order to survey different sites for a possible usage of drones.
After a quick reflexion, it was decided that the constraints would be the following:

  • The case should be portative enough to fit inside a normal bag or even a leather satchel/bag.
  • The case should be powered either by direct power (AC inlet) or an internal battery.
  • The case should obviously be waterproof.
  • The case should be able to be used for at least 5h on battery.
  • There should be a screen to visualize the data quickly in a few minutes (a 'quick survey' mode).
  • It should use the same components as on the drone we want to use after, to have a data consistency.
  • The data should be stored inside a log, whatever the form, so the data can be reviewed later.
Obviously, some other constraints were imposed due to these first constraints or for other factors:
  • If the case is to be used for travelling, then the internal battery should be taken out during a flight dor example, due to all the regulations with batteries. So it should be a battery that can be quickly plugged in/out of the case. So, as the battery has some chances on going on the bottom of the case - for balance and placement reasons - the top of the case should be removed easily to put in the battery.
  • The compass should be external, plugged on the outside of the case, so the box itself doesn't generate magnetic interferences that are recorded.
  • It should be possible to recharge the battery while powered on ground power, so a transformer must be used, which, due to size constraints, will mean that it's gonna emit a bit of heat: some openings should be done on the 'top cover' so that the heat spreads out evenly inside the box.
  • There should be some buttons, at least to power on/off and change the power source (battery/ground power).
  • Who means logs means files, means an easy way to move it from the box to a computer: I will store the logs on an SD card, which should be easily exccessible.
After some reflexion and a day to look for every component I want in the usual places (Conrad, Distrelec, Digitec and some others...), I finally have a BOM fixed with as main components: the usual raspberry pi, a raspberry pi touchscreen/display, a few buttons, a sheet of PVC to mill, a waterproof case.
I already have one instance of the magnetometer I want to use - a AK09916C based board - and of the desired GPS - a ublox NEO M8N.
For the 4G Modem, I also already have 'in stock' what I want to use: a USB based Hologram 4G Modem called Nova, with an external antenna.