Hotspot Setup

Overview

In order to get the most out of DMR having a hotspot is key. I chose to go with a duplex hotspot to be able to take advantage of two timeslots. The instructions provided may not work exactly for all types of hardware.

Parts

• Raspberry Pi 4 (2GB, 4GB, or 8GB)
• Raspberry Pi 4 Power Supply
• 16GB microSD Card
• Raspberry Pi 4 Case w/ Fan & Heatsinks
• Duplex MMDVM Hat w/ OLED Screen

Tools

• Philips-head Screwdriver (one of these came with my Pi Case)
• Soldering Iron (for upgrading the MMDVM hat firmware, or when using a fan, which is highly recommended with the Pi 4)
• Snips/Diagonal Cutters (for trimming the case cover)

Prerequisites

• A DMR radio configured for the hotspot frequencies and color code (configured later). See my documentation for configuring the Radioddity GD-77 with OpenGD77.
• Register and apply for a DMR ID via radioid.net.
• Register a BrandMeister account and configure hotspot security. Make sure to select Chinese Radio for Brand if using the GD-77.

Assembly

• Apply the heatsinks to the Pi.
• Mount the Pi into the case with the provided screws.
• Attach the MMDVM hat to the top of the Pi.
• Attach the two UHF antennas.
• Using snips, remove the portions of the case cover that would interfere with the antennas or the screen.
• Using two of the provided screws that came with the case, attach the fan to the top of the case.
• Cut the leads then route the fan cable through one of the remaining slots beside the fan on the top of the case.
• Solder fan leads to 5V/Ground on the MMDVM Hat.

- Install the top of the case.

Install pi-star

• Vist the pi-star download page and download the latest version with the Pi-Star_RPi_ prefix. At the time of writing this, it was Pi-Star_RPi_V4.1.5_21-Jun-2021.zip.
• Write the image to your microSD with either balenaEtcher or the official [Raspberry Pi Imager](Raspberry Pi Imager.
• Configure WiFi with the pi-star WiFi Builder. Write this file to wpa_supplicant.conf on the boot volume of the microSD. On macOS, the following command should work:

  cp Downloads/wpa_supplicant.conf /Volumes/boot/wpa_supplicant.conf
  

Configure pi-star

Basic configuration

• Upon first boot (and after some time), the Pi will connect to WiFi and will available via pi-star.local
• Login to the configuration page using the username pi-star and the password raspberry. Change the password via the Remote Access Password section at the bottom of the page. Changing the password will require you to log back in.
• Under Control Software set Controller Mode to Duplex Repeater (or Half-Duplex on Hotspots) and apply the changes.
• Enable DMR Mode under MMDVMHost Configuration and set MMDVM Display Type to OLED Type 3. Apply the changes.
• Under General Configuration set all of the following, then apply changes:
  • Hostname (optional) - change it to the hostname you prefer. You will be able to reach this by adding .local to the end.
  • Node Callsign - set to your callsign.
  • Radio Frequency RX/TX - pick frequencies that aren't associated with a repeater or hotspot near you. Most hotspots only come with UHF antennas so pick a frequency in the apprropriate band.
  • Latitude/Longitude - Use Google Maps to figure this out.
  • Town - Add your town followed by your locator/grid square (available on your QRZ page).
  • Country - Add your country (e.g. USA).
  • URL - If you want it to use your callsign's QRZ page, select Auto, otherwise select Manual and populate the url with the url of your choice.
  • Radio/Modem Type - Choose STM32-DVM / MMDVM_HS - Raspberry Pi Hat (GPIO).
  • Node Type - Select Public.
  • APRS Host Enable - Enable.
  • APRS Host - Choose the host that is appropriate for your location (e.g. noam.aprs2.net).
  • System Time Zone - Don't change UTC.
  • Dashboard Language - Choose the apropriate language (e.g. english_us).
• You will now get a warning about the hotspot being in public mode without an access list. Add your DMR ID to the DMR Access List and apply the changes.
• Under DMR Configuration set all of the following, then apply changes:
  • DMR Master - Select the BrandMeister master of your choice (e.g. BM_3104_United_States).
  • DMR ESSID - Because later versions of DMRGateway have stronger opinions about this, I chose to set this to 01 for my first hotspot.
  • DMR Color Code - Pick the CC you prefer.
• You will now see Hotspot Security under DMR Configuration. Insert your hotspot password and apply the change.
• Under Firewall Configuration change uPNP to Off as this isn't needed for DMR.
• Click on Configure WiFi under Wireless Configuration. Add the details for your phone's hotspot network and save the changes.
• Set the PSK for the Auto AP near the bottom of the page.

Advanced Configuration

• Set you Brandmeister API key here. Your BM API Key can be generated here.
• Set your callsign and enable PiStar-Remote.

Update Pi-Star

Login via SSH and run the following command:

sudo pistar-update

Upgrade MMDVM Firmware

The latest version of the MMDVM HS_Hat firmware at the time of this writing is 1.5.2.

To upgrade the firmware, perform the following:

• Jumper BOOT0 (center to +) and solder a bridge on JP1

• Run the following at the terminal on the Pi:

  sudo pistar-mmdvmhshatflash hs_dual_hat
  

• After upgrade, remove solder bridge from JP1.

• Remove BOOT0 jumper (optional).