|WA8LMF Home Page | Main APRS Page | Updated 12 Dec 2007|
This packaging for the TinyTrak3 APRS tracker, from Byonics, was developed to:
The metal chassis is a standard LMB utility box measuring 1.25" x 3.2" x 2.2". This box is exactly the right width for the standard TinyTrak 2 or 3 board to fit across the width with the DB9 connectors extending out each side. The first view below shows the serial port connector for a GPS device and a PS/2 connector to provide +5VDC power to typical mouse-type GPS devices. These GPS units are normally used with laptop computers and powered from the keyboard jack of the laptop.
The 3-position center-off toggle switch switches power to the TT and selects either the primary or secondary mode depending which way from center the switch is moved. The red pushbutton is connected between the PTT-IN line (TT3 radio connector pin 8) and ground. It allows a posit to be sent on-demand if the Mic-E mode is checked in the TT configuration software. The four holes in a row allow the LEDs of the TT board inside to be seen. The two holes at the far end allow the carrier detect (R9) and TX audio level (R6) to be set without opening the box.
A view from the other side, showing the radio interface connector J1 . Note how the flange on the upper half of the utility box was notched out about 1/16 of an inch to allow the TT circuit board inside to rest the right distance from the upper surface of the box. The bolt between the LED holes and the adjusting holes is the only fastener securing the TT board to the inside of the cover.
The bottom of the box has a 1" x 2" patch of the hook-half of the super-heavy-duty Velcro sold in southern California as "Quake Grip" glued to it. This stuff hooks and clings powerfully to automotive carpeting. When this device is used in a temporary mobile setup, I just stick the box to the carpeting on the transmission hump.
Interior view showing the full-sized TO220-package 7805 5-volt regulator mounted to the end of the chassis for heat sinking. Note how the standard TT3 circuit board exactly spans the width of this box. The only fastener securing the TT to the box is the #6-32 bolt and nut in the center of the PC board. A 1/4" thick nylon spacer is sandwiched between the TT board and the inside surface of the case. The PS/2 connector was salvaged from the mouse port backplane strip of an old PC and epoxied to the case. The nearest part of the chassis as viewed below has exactly the right amount of space for a standard 9-volt battery with snap to fit in from left-to-right. +12 VDC brought in from the radio connector and +9VDC from the battery are combined using two diodes so that the battery never gets used in normal operation. When the unit is separated from it's normal harness (and the source of +12 volts) for programming, the internal battery automatically starts powering it for convenience.
The male DB9 assembly that plugs into the TT radio-interface connector has two cables coming out of it. One is a 6-conductor cable cut from a PS/2 mouse/keyboard extension cord, wired to mate with the 6-pin mini-DIN packet/data connector on several of my transceivers. The other cable is 22-gauge red/black zip cord with a 1/2-amp inline fuse holder terminated in Anderson PowerPoles. On all the radios I intend to use this device with, I have spliced a 6" red/black pigtail, with matching PowerPoles, to the main +12 VDC red/black power leads a few inches from the back panel of the radio. I use the Scotch-Tap crimp-on splices commonly used to steal power from car tail light leads for trailer lights.
The full-sized 7805 supplies power only to the GPS. The TT's original 78L05 continues to power the TT board. The GPS power remains live, even when the TT is switched off, so that the GPS can continue to keep it's position and ephemeris current. Switching from primary mode through OFF to the secondary mode won't knock the GPS out of lock by momentarily removing GPS power. Ultimately, I intend to replace the 7805 with a miniature AstroDyne high-efficiency DC-DC switching converter that will cause a 100mA-at-5 VDC GPS to draw only about 40mA at 12 VDC. This drain is so small that the GPS could be left on and live for weeks at a time without draining the car battery.
Note also how I nibbled and filed the chassis half with the PS/2 jack on it, so it would fit snugly against the DB connectors when assembled.