MMDVM Pi-Star Hotspot - Quick Replacement of the SD Card (Repair Notes)

 

In recent months the web server in my MMDVM Pi-Star hotspot has been failing during operation. The TX/RX from the hotspot continued to work, but any opportunity to interact with the device using the web server resulted in the pages not loading.

Yesterday I decided to entirely rebuild the unit's SD card using the following process. These notes are as much for me if I need to repeat the process again in the future.

Failure of SD cards is very common after continued use, especially in devices like this that run 24/7. The entire card might not fail, but sectors on the card can easily fail.

Steps

• Rebooted the hotspot and got access to the web interface temporarily.
• Took a current backup of my settings and downloaded/saved the file on my laptop.
• Note, this method requires Wi-Fi so a laptop or desktop with Wi-Fi capability is required.
• Slow formatted a replacement SD card to verify that all sectors are good.
• Downloaded the latest Pi-Star image from Pi-Star Downloads - pistar.uk
• Flashed the new image to the new SD card using the Raspberry Pi Imager app Raspberry Pi OS – Raspberry Pi
• Power down the MMDVM hotspot, full out the old SD card and replace with the new SD card
• Boot the MMDVM hotspot off the new SD card, leaving LOTS of time for initial boot steps to occur and the setup Wi-Fi access point to load (SSID = Pi-Star-Setup)
• Connect the laptop to the new temp SSID and load the start-up pages for Pi-Star
• Go straight to Configuration > Backup/Restore
• Load the backup file from step 2 and upload the file and Restore.
• Go back to Configuration and change the Wi-Fi settings to the stored settings from your home network (settings were stored in the backup and just need to be selected and applied.
• Reboot the MMDVM hotspot and everything should come up just like before the new card was installed.

High Bit Rate Error Tweaking

My particular MMDVM hotspot came with a sticker indicating the frequency offset preferences for TX and RX. In the case of my unit that was an adjustment of -475 for each.

When receiving from the Parrot Reflector I noticed that the bit rate error was as high as 4% and adjustment was required. I found a good instruction from someone and followed it to make quick work of the problem. Like tuning an antenna you make some broad adjustments, then when you find the range where it's working better you begin to dial in the better settings by making smaller changes in either direction.

These edits are made at Configuration > Expert > MMDVM

Here is a short summary of my adjustments and how they were working.

-475 = 4% BER (not good)

-575 (broad change of 100) = .5% BER (very good)

-675 (broad change of 100) = 1.2% BER (trending worse)

-625 (medium change of 50) = 1.1% BER (trending better)

-575 (medium change of 50) = .8% BER (very good)

-525 (medium change of 50) = 1% BER (trending worse)

You won't get identical readings on each transmission, but you can see that at -575 RX Offset I received the lower settings of .5% - .8%. After two readings below 1% BER, this was the setting that I left it on for RX. TX remained at -475 as per the manufacturers' sticker.