HT GPS + Audio: Hardware Overview

The project has two circuit boards:

  • a modified TinyTrak3 kit for GPS-to-AFSK
  • a custom PCB for everything else

The boards fit in the two halves of the enclosure, which is held together by four 7/8-inch 2-56 machine screws. The blind holes in the lower (right) half are tapped for the screws. The clearance holes in the upper (left) half are a bit too close to the interior; if the setup isn’t perfect, they break through.

The right half slides into the HT’s battery pack grooves. The two tin plates match up with the HT’s power input contact springs.

Interface - top and bottom surfaces
Interface - top and bottom surfaces

The oval mark around the four LEDs is actually a 1 mm deep recess in the cover; the LEDs are the tallest things on the board and I sort of ran out of room. The GPS connector is essentially flush against the back of the HT, so the board can’t get any lower. Even though the case halves are milled from a hulking 3/4-inch plastic plate, the top surface is only 1 mm thick above the LEDs, so the board can’t get any higher.

The interior view:

Interface box - interior
Interface box - interior

The DB-9 serial connector mounting screws hold the TinyTrak3 board in place. The GPS receiver and PC serial port (used for configuration) plug into that connector.

The four external cables connected to the circuit board:

  • power from external battery pack
  • helmet mic + earbud
  • PTT switch
  • HT speaker + mic + mic power

A closeup of the audio PCB in its natural habitat:

GPS + Audio circuit board
GPS + Audio circuit board

The two nuts on the right fit on 4-40 brass screws that I converted into studs under those tin battery pack strips, about which more later. The nuts hold the circuit board in place atop a shoulder around the interior of the compartment.

The OEM battery packs have nice tabs that engage the HT’s clever pushbutton latching mechanism. I spent a lot of time staring at them: they’re easy to do in an injection mold and impossible to machine at my skill level. So I punted: two strips of tape hold the enclosure in place on the HT. Works fine.