|SVT MMDVM first calls
The Digital Voice ( DV ) for the ham radio have started a few years ago but to build a hotspot ( a tiny personal half duplex repeater ), you will need some pricey equipments like DVStick with AMBE-3000 vocoder and USB interface plugged into a Raspberry Pi with an Arduino Mega to drive the UHF transceiver.
It all started around Sept 2017 when the price of DMR radio was getting below RM1,000 and a few of us purchased a TYT MD-2017, one of the more popular DMR radio at that time.
Secondly, without a DV hotspot, having a DMR radio is kinda useless unless you are within the range of a DMR repeater in your area.
Thanks to Jonathan Naylor G4KLX ( https://github.com/g4klx/ ) (and many many people people) that created the MMDVM, a software that integrated multiple hardware ( teensy, Arduino DUE, STM32F1, STM32F4 ) and Raspberry Pi running pi-star ( https://www.pistar.uk/ ).
When I saw the hardware requirements, I noticed that I actually have ALL the hardware with me, STM32F103 red-pill, Raspberry Pi and they were also using a version of Arduino called stm32duino.
|A few STM32 red-pill I purchased previously
The only missing piece was the UHF transceiver called RF7021SE module plus changing the TXCO to 14.7456Mhz. So I started doing my research on different board designs and immediately design a single board layer to test out my design.
Here is the first version after many iterations and because it was a single layer board, I had to place the SMD LED at the bottom of the board.
|SVT MMDVM 3D view
Once my designed was almost finalised, I bring it to Uncle Chow ( 9M2CF ) to convert my PCB design to a single layer PCB.
|SVT MMDVM negative
|SVT MMDVM etched
|SVT MMDVM copper removed
After some UV exposure and chemical baths, I got the SVT MMDVM board ready to be soldered.
|SVT MMDVM fully soldered
|SVT MMDVM top side with red-pill
|SVT MMDVM running
Fully connected to the RPI 1 and pi-star software loaded.
|SVT MMDVM connected to RPI 1