VE6NHM Phase 2 using the Raspberry Pi HAT and interface board

The second phase of this project replaced the controller with a new Pi HAT implementation that provides digital control, DTMF decoding, analog voltage monitoring, phone patch and linking capabilities over ethernet. The board was realized using 0805 surface mount components, and was factory built. The interface board was realized in through-hole component to make it simpler for amateurs to modify or customize.

The connector on the Pi HAT is a standard 8-pin ethernet type, with LED’s to indicate power on and PTT status. It is wired to an interface board, that was cloned from the previous Arduino board in Phase 1, but without the PWM capability and with adjustable audio levels in and out. Connection to the radio was maintained with the same RCA type jacks, and the power, COR and PTT are connected to a barrier strip on the board. COR Sensitivity is programmable by a jumper on the board.

The software was implemented in a 3-layer ‘sandwich’, the lower layers implement the FPGA control and DTMF decoding, a middle layer supplies a digital audio tap and real time audio transmission, and the upper layer provides configuration using an HTML interface and a SIP client for connection to a VOIP PBX. A phone patch to an asterisk PBX was tested and completed, also linking between repeaters using the USRP protocol was added.