Creating the LED matrix (2 of 2)

Step 15: Creating the LED matrix (2 of 2)

Now that things are trimmed out, time to start mounting and wiring all 320 LEDs. Making a couple of jigs will speed up this process considerably.

First, since LED multiplexing requires the LEDs in the array to be wired with cathodes one direction and anodes another, make a holder like the one shown in the pic to bend the leads of the LEDs accordingly, and trim off the excess. Make sure that one side is bent taller than the other to prevent any leads crossing and power shorts. (pic 2)

Repeat this process for all the LEDs in your matrix, minus how ever many columns your matrix has in it. If you've got an 8x40, that's 320 LEDs, minus 40 columns = 280 bent LEDs. For the remaining 40, only bend the taller of the two leads, and leave the second one straight.

Once all the leads are trimmed, make a new jig out of any scrap material you've got that is flat on one side, at least 0.5 "x .5" x 0.3" - I used aluminum square tube. Drill 8 holes in a line the exact same spacing as in your PET sub visor. (pic 3)

Place 7 LEDs with 2 bent leads, and one of the LEDs with just one bent lead into your drilled holes and solder the connectors of the lowest-sitting leads together. When finished, you should have a line of LEDs with all anodes soldered together, and one straight lead at the end. Repeat this for as many columns as you have in your matrix (for me, it was 40) Its a good idea at this time to paint the backsides of the LEDs black to avoid light coming back into the helmet while you're wearing it. I waited until later and it was a bit of a pain to do. (pic 4)

With all 40 columns built, place them into the subvisor in blocks of 8, and solder the remaining connections. Be careful not to drip any solder across the joints or onto the subvisor. Solder these where they will be mounted in the subvisor, as each section will have a slightly different curve to it. (pic 5)

Once soldered, you can remove the LEDs from the subvisor by pressing lightly on the front of them. Remove the 8x8 units and solder up the connections to the rows and columns. Keep your wiring tidy and try to run the lines up one side of the display - using heat shrink tubing can help make sure things route the right way. (pics 7 & 8)

After all the wires are connected, re-install the LED arrays and run the wires up to the MAX7219/7221 chips mounted on the sub visor. (pic 9) When mounting the MAX7219/7221 chips to the subvisor, make sure to isolate them against electrical contact with a small rubber pad. Aluminum is conductive and can short out your matrix!

After the LED matrix is wired, connect the 5V, GND, clock, data and latch connections on the matrix boards and leave some length on the wires to connect to the arduino once the subvisor is installed in the helmet. (pic 1)

Materials needed: