DIY $45 Digital Radio Hotspot for DMR/FUSION/D-STAR: Easy Setup, Zero Soldering!

Creating your own MMDVM Raspberry Pi hotspot is an enjoyable and affordable way to dive into the world of amateur radio digital modes and networks. With simple steps and no need for soldering, this guide will walk you through gathering the necessary components, assembling your hotspot, and setting it up with Pi-Star, the software that powers your device. Let's get started!

What You'll Need:

• Raspberry Pi Zero WH (with headers): This compact version of the Raspberry Pi comes with pre-soldered GPIO headers. Adafruit Store (Cost: $16)

• MMDVM Hotspot Hat + Case + Antenna + Screen Kit: This kit includes everything you need to turn your Raspberry Pi into a digital mode hotspot. AliExpress (Cost: $17)

• Pi Zero Power Supply: To ensure your Raspberry Pi has a reliable power source. eBay (Cost: $7)

• MicroSD Card (8 GB minimum): For installing the Pi-Star operating system. eBay (Cost: $5)

Supported Digital Modes:

Your hotspot will be able to connect to various digital modes, including:

• DMR

• D-Star

• Fusion

• P25

• NXDN

Setting Up Your Hotspot:

Flashing Pi-Star onto the MicroSD Card

1. Download Rufus: Head to the Rufus website and download the latest version for your Windows PC. Install Rufus by following the on-screen instructions.

2. Download Pi-Star: Visit the Pi-Star website to download the latest Pi-Star image file. Extract the .zip file to a folder on your PC.

3. Prepare the MicroSD Card: Insert the MicroSD card into your computer's card reader. Ensure it is recognized and assigned a drive letter.

4. Configure Rufus:

• Open Rufus and select your MicroSD card as the "Device".

• Click "Select" to choose the Pi-Star .img file you extracted.

• Set the "File system" to FAT32 and leave the "Cluster size" on default.

• Optionally, name your Pi-Star card under "New volume label".

5. Start Flashing: Click "Start" in Rufus. Confirm you're okay with erasing the MicroSD card's data and wait for the flashing process to complete. Close Rufus and eject the MicroSD card safely.

Assembling the MMDVM Hotspot:

• Begin by acquiring the necessary components for the MMDVM (Multi-Mode Digital Voice Modem) hotspot: a Pi Zero with pre-soldered headers from Adafruit, the hotspot HAT (Hardware Attached on Top) purchased from eBay, and a micro SD card with Pi-Star software already flashed onto it.

• Note the offset values provided on a sticker with the HAT. These values are crucial for configuring the hotspot, especially for Fusion or DMR modes. They will be used in the Pi-Star configuration under the MMDVM host and expert settings, though this guide won't delve into those specifics.

• Unpack the HAT from its RF or static prevention package. Set aside the case and antenna that come with it, as they are not immediately necessary.

• Examine the HAT, identifying the small screen and jumper positions. Notice the pre-soldered areas for connections, which will be important for assembly.

• Prepare the Pi Zero by removing it from its packaging. The advantage of using a Pi Zero with pre-soldered headers is that it eliminates the need for soldering, making the assembly process easier.

• To attach the HAT to the Pi Zero, you may need to modify the Pi Zero by clipping off any pins that could interfere with the HAT's placement, ensuring a fit without soldering.

• Insert the micro SD card with the Pi-Star software into the Pi Zero.

• Assemble the hotspot into its case. The case is designed to house the Pi Zero snugly, with screws and spacers provided for securing the components. Note that using a Pi Zero with headers may cause it to sit lower in the case, which might lead the screws at the back to protrude slightly. To mitigate this, apply stick-on rubber feet to the bottom of the case to elevate it, preventing the screws from scratching surfaces.

• After securing the HAT to the Pi Zero within the case, connect the device to power. Initially, it will create its own Wi-Fi access point named PI-Star, which you can connect to with a phone or computer to begin configuration.

• Log in to the Pi-Star dashboard using the default credentials (username: pi-star, password: raspberry) to configure your hotspot. Enter your callsign, select your time zone, keyboard layout, and configure the modem type to match your HAT.

• Adjust the hotspot's settings to match your specific digital mode requirements (e.g., DMR, D-Star, Fusion). Each mode may have unique settings for optimal operation.

• After configuring, the hotspot's screen should activate, displaying its status. Further adjustments can be made via the Pi-Star dashboard to refine its operation.

Programming Pi-Star for DMR:

• Begin by performing a factory reset on your Pi-Star device to start with a clean slate. Navigate to the configuration menu and select 'Factory Reset.'

• After resetting, access the dashboard to confirm that no mode is currently defined, indicating you're starting from scratch.

• Proceed to the configuration section. Ensure the control software is set to 'MMDVMHost' and the node type is 'Simplex Node.' Apply these settings, which may take about 15-20 seconds to process.

• Upon successful application, you'll be prompted to re-select your modem. Choose the appropriate option that enables DMR mode on your hotspot.

• Adjust the 'hang time' settings if you plan to operate multiple modes simultaneously. The default is set to 20 seconds to prevent immediate mode switching, allowing for a pause in conversation before scanning for the next active digital mode.

• Enable DMR mode specifically and set the display to OLED to ensure you can see the hotspot's status and activity. If using an advanced external display, select the appropriate option here.

• Leave the 'Nextion Layout' and 'Port' settings as default unless you have a specific need to change them.

• Apply these changes and wait for the confirmation screen, indicating your hotspot is now configured for DMR mode.

• Move to the 'General Configuration' tab to enter your personal call sign and DMR ID. These are crucial for the hotspot to function correctly in DMR mode. Ensure your DMR ID is registered and activated within the DMR network.

• Select a UHF frequency for your hotspot that is accessible by your radio and not in use by local repeaters. Consider any frequency restrictions of your radio to avoid potential issues.

• Fill in your geographical details, including latitude, longitude, city, and add a URL for your QRZ bio if desired.

• Choose the correct radio/modem type for your setup. For this guide, select 'STM32-DVM / MMDVM_HS - Raspberry Pi Hat' or the equivalent that matches your hardware.

• Set your node type to 'Private' and adjust the time zone according to your location.

• Apply these general configuration changes and prepare to select a server for DMR operation. Choose a server that matches your geographical location for optimal performance.

• Define the color code for your area, a crucial setting for DMR operation to ensure compatibility with local standards.

• After applying these settings, navigate to the 'Expert' section for advanced configuration, specifically the MMDVMHost settings. Here, you may need to adjust the transmit and receive offsets to match the specific requirements of your hotspot, ensuring optimal performance and minimizing bit error rates.

• Test your setup by making a contact, adjusting the offset settings as necessary to achieve the lowest possible bit error rate.

• Use your DMR radio to connect to talk groups and make contacts. Your hotspot should now be fully operational in DMR mode, ready for you to explore the wide range of talk groups and digital modes available.

You did it!

With your MMDVM hotspot assembled and Pi-Star programmed, you're all set to explore the digital modes of amateur radio. We hope this guide has made the process enjoyable and straightforward.