The device in question is of course a DV hotspot, now there are loads out there, however until now none of these are cheap... until now that is.
China, a country well known for cheap products, has produced boards that essentially are Raspberry Pi HATs that work as DV hotspots that support modes such as DMR, Yaesu System Fusion, D-STAR, P25 and NXDN (though the latter 2 aren't used in the UK that I know), you can get these assembled in a case with a Pi (or Pi Zero) or for a little cheaper get the parts and assemble them together, the software side is in the form of an SD card image for the Pi called Pi-star, which must be configured to work with the Raspberry Pi and the MMDVM HAT you have on the Pi.
There are instruction videos already on YouTube on how to set these up so I won't be covering that aspect here, as I am going to buy the HAT and the Pi as separate items and assembling them together which will be filmed and uploaded to my YouTube channel.
Powering this unit simply requires a micro USB cable and a mobile phone charger, even one of the widely available power banks can work for this use, I have a Goodmans 8000mAh power bank that could run this sort of setup for a few hours in the event of being away or without mains power, though it still needs the Internet which my mobile phone and tablet can provide as I suspect data use is small, at home I simply just plug it in somewhere in the shack, sit in the living room and have QSOs on DMR, in the car I can use Fusion (I may get a second unit for the car for exclusively this and add the frequency manually to the FTM-400 with TX at low power of course.
I have ordered the Pi Zero W I need for this already (it's like building a house, you have to start with the foundations on which to build), the next order should be for the module, some of the ones from China come with a case and OLED screen so I need not have a display attached to the Pi Zero at all, I am also in the process of getting the Pi-Star image ready, that needs to go onto an SD card which I will purchase locally.
Knowing a Pi Zero can hold a decent uptime I may leave this thing powered up and connected so all I have to do is run the radio.
A bit of programming of the radio will also be involved of course but that's no problem as the codeplug software is on the computer already.
73 de 2E0EIJ