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My First Tagger:
Build the Sensors

I wanted to have the usual three sensors on a hatband. I thought about trying to put two or three of the IR sensor components on a board, like FragTag's sensors, to give a wider angle of detection. The ±45° angle of half-sensitivity of the TSAL 4840 would seem to mean there would be areas of reduced sensitivity, and that perhaps five head-mounted sensors would give better coverage (4 around the perimeter, one pointing straight up). Still, half sensitivity isn't necessarily the desired level of coverage; perhaps six sensors around the perimeter would be even better. I also thought about putting sensors on a vest, in addition to the hatband. That sounded like it might be good, since I want to keep center-of-mass shots as a viable target. However, the hatband sensors seem sufficient for others, so it sounded like a good place to start. Besides, if I'm dissatisfied, I can always add the vest sensors later.

bare sensor boards sensor board sensor boards
The sensor boards, without components. A sensor board. The sensor boards.

The sensor is a much smaller and simpler board to assemble than the main board. I omitted the IR LED circuit, as it's not used in the current Miles Tag firmware, and it apparently interferes with the sensor's ability to receive data while the player's hit LEDs are on (as they are when "dead"). I assembled them resistors first, then the TSOPs, then the hit LEDs, and finally the capacitor. I then added the coiled 4C wire to one of the boards, and a straight 4C wire to each of the other boards. The coiled wire was cut from a telephone handset cord with a 4P4C connector on the other end, and is used to connect the sensor assembly to the tagger. The two straight wires were 4-conductor telephone wire, and are used to connect the sensor boards to each other.

A note of caution: some telephone handset cords are not suitable. I was lucky with my first one: it was made with stranded wire. The second one I obtained was made with some strange wire substitute, which seems to be made of a synthetic fiber core spiral-wrapped with very thin copper foil. It must work fine for a handset's crimp terminal, but it falls apart when soldered.

sensor subassembly attaching the base dome
Wired board (and test-fit of unattached base and dome). Attaching the base with sinew thread. Sensor dome with notch.

Each sensor board was mounted on a base made from a flat piece of 1/8 inch thick ABS plastic. The mounting could have been done in many ways. I came up with a method that seems well suited to the do-it-yourself style of work, although I'd not expect it to be cost effective for industrial use. Since each board has a few unused holes for the unused IR LED circuit, I drilled a pair of matching holes in the base. A piece of split artificial sinew (very much like dental floss, but brown) was passed through the base holes and the IR LED holes on the board, and then tied above the board. This keeps the board secure against the base, which is nonconductive and very sturdy. The board can wiggle slightly, but when the dome is attached, the wires keep anything from moving. I tied a second piece of sinew through the wire connection holes on the end board, since that board only has one wire coming from it.

dome attached sensor unit sensor hat
The end sensor, with attached dome. The completed sensor unit. The sensor unit on a patrol cap.

The domes are chem-welded to the bases. To allow the domes to contact the bases as much as possible, a notch is cut in the dome to allow the wire to pass through. The notches are cut slightly small, and are given a rough toothed upper surface, to pinch the wire in place and provide some strain relief. After the weld solidifies, the base is trimmed to the dome outline, taking extra care near the wires. I left a small tab of the base material under each wire, and gave the tabs a saddle shape, so that I could wrap the wire-dome junction with cord if I need extra support for the wires. (I wrapped the wire with masking tape while working on the base, to avoid damaging the outer insulation.)

To mount the sensor unit on a cap or hat, I used self-stick hook-and-loop fastener (Velcro or something like it). I attached a strip of the hook tape to each base, and a strip of the corresponding loop tape at three points on the cap or hat. The black wire stands out a little more than would be perfect, but I didn't have a source for foliage green 4-conductor wire. I did find a source for foliage green velcro, though, but it isn't self-stick.

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