After the DMR Quick Start presentation, Eric (VE3EB) and I (VE3IBW) had many inquiries about which MMDVM hat for a Raspberry Pi that we bought to make our Digital Hotspots.
MMDVM_HS_Dual_Hat Duplex MMDVM Hotspot P25 DMR YSF NXDN Pi Revision 1.3 + OLED
On eBay: https://www.ebay.ca/itm/173398296164
The fun thing about this RPi Hat is that it is a duplex board and supports five modes: D-Star, DMR, YSF, NXDN, P25. Duplex MMDVM boards give your hotspot a repeater feel and allows you to transmit on one DMR Time Slot while the other one is in use. Very handy for sending a message to TG 4000 to end a QSO on a busy TS. There are simplex boards too that cost less.
This MMDVM hat comes with a very small OLED screen already soldered onto the board. Handy and fun to see who is talking and the IP address of the RPi when on your QTH network.
The hat is purported to support all RPi models. It plugs into the GPIO bus of the RPi. I use an RPi 3A+ for its speed, memory footprint, and low power draw. Some others in the club prefer a 3B+ or 4 because it has an ethernet jack. I bought the RPi at Elmwood in Toronto. Had to pay shipping, but the overall cost was quite cheap.
Whatever mode you choose, having a gateway onto the various Digital Amateur networks (and there are many) makes these digital modes a lot more fun.