Arduino (Mini) Duplex MMDVM hotspot firmware update, there is a design fault which has left pin 20
on the STM32 not connected, which is the write enable pin for firmware update. In order to correct
this you will need to short pin 20 & 23 together or if you are not good with a soldering iron pin 20 to Ground.
The images below show both methods. The modifications can be made with a standard soldering iron.
Warning if you are not confident at soldering do the second method, if you accidentally short to the adjoining pin you will not damage it, whereas pin 24 is +ve and if you accidentally short pin 23 to 24 you will damage the MMDVM hat and your pi.
NOTE M17 requires the WPSD version of pi-star to be able to upgrade to v1.6.1 firmware.