The beacon controller is assembled from ready-made modules Arduino UNO / NANO / Pro mini + si5351 module.
RTS DS3231 or GPS module NEO-6M can be used as a time source.
Ext BPF - PD5/PD6/PD7/PBO, Ext PA - PB1.
For flash hex, bootloader chip45boot2 is used.
Description and updates - https://r0aek.me/?p=1862
If you are having difficulties translating from Russian, please use google translator.