Unlike all the V1 TeensySaber electronics, the V3 board is not something I recommend that most people build themselves. All the instructions for doing so are available here, but most people should just continue reading to find out how to use the board. What you will need: Teensy 3.2 - the brains (It is also possible to use a Teensy 3.5 or 3.6, but I think the 3.2 is best because it's smaller.) TeensySaber V3 - light, sound, motion (you might be able to buy one here or here.)
Important! Make sure you cut the lead between VIN and VUSB on the teensy before you solder it to the TeensySaber V2. Cutting it afterwards is not nearly as fun. (But possible with an exacto knife or similar.) Note that after you cut VIN/VUSB, you'll need to provide external powre to use or program the teensy. Once attached to to the TeensySaber, it will draw power from the battery to power the Teensy.
Once that's done you need to solder your TeensySaber to a Teensy. For a Teensy 3.2, here is where you place all the pins:
The easiest way to solder the teensy to the teensysaber board is to use header pins. However, once joined in this way, it's quite difficult to get them apart again, which means that if one of the boards develop a fault, you pretty much have to throw away both of them. What I recommend doing is to use header pins only in two corners, then use some regular wire for all the other connections, that way you can cut the wires and desolder everything fairly easily should you need to. (Full disclosure: I have not tried this yet, but I have ruined a few boards while trying to get the pins out...)
Anyways, put the teensy 3.2 on top and solder the pins/wires into place. (top and bottom) Later, we'll cut or bend the pins to make sure they aren't in the way. When you're done, it should look something like this:
Note: Pins marked with * are ones that you probably want to hook up to something. The rest of the pins are usually ignored.
Battery+ - 2.6 to 4.5 volt input, drives everything except the LEDs
Battery- - negative pad for LEDs, needs to be at same level as GND when both are connected.
GND - ground for electronics except LEDs. Note that GND is also available on short edge of the teensy. (See the teensy pinout for details.)
Speaker +/- - hooks up to speaker
Power / AUX / AUX2 Button- Hook up to closing buttons, or potentially touch buttons.
Blade ID / neopixel data - Normally used to measure the blade ID restor, and if it's a neopixel blade, feed out neopixel data. For a fixed non-neopixel saber, it could be repurposed.
LED 1, 2, 3 - Hooks up to negative side of LED (positive side of LED hooks up directly to battery.) These pads can handle up to 30 volts.
LED 4, 5, 6 - Like LED1/2/3, but requires FETs to be placed on the bottom of the board to function. Voltage is limited by selection of FETs.
Power 1, Power 2, Power 3 - These control the FETs which drive LED 1, 2, 3.
AUX LED 1, 2, 3 - These are hooked up to pads on the bottom which can be populated with FETs and used to drive additional LEDs. If the bottom FETs are not populated, these pins are free and can be used for any purpose.
Free pins - these are not used for anyting and could be hooked up as additional inputs or outputs. Pins marked with "PWM" have hardware PWM support which can be used to control the brightness of LEDs or drive servos.
Data In, Data Out, SCK, SD card select - these pins are used to communicate with the SD card.
SDA, SCL, Motion Interrupt - these pins are used to communicate with the gyro and accelerometer chip.
Battery Volt Sense - used to read battery voltage.
Amplifier enable - Used to control the amplifier.
5v - generated by the TeensySaber board.
3.3v - generated by the Teensy
Wire gauges
Most pads on the teensy will not need to carry any significant amount of power and can use 30 awg (very thin) wire if you choose. However, Battery- will carry the combined power of all your LEDs, and LED 1,2,3 (and 4,5,6 on the bottom) will carry a fair amount of power as well. It is recommended to use thicker wires, for these wires. There is no absolute rules for what wire guages are required, but here is a helpful chart. (See the "chassis wiring" column.) Keeping the high-power wires short helps as well.