RaveSaber - AVR Hardware

This repository contains the circuit diagram, PCB schematics, prototype board layout, parts list, & setup guide for the RaveSaber electronics.

There is no blade or hilt at the moment, but you can swing the LEDs around using the PCB or prototype board & a piece of wood.

Electronics Design

The Rave Saber board includes voltage regulation, utility headers, input buttons, and an Atmel ATmega168a microchip.

Connectors

J1 is where power enters the board from the battery. We use JST connectors for our battery wiring. The battery power is fed through the power sub-circuit to get a regulated voltage of 5V.

J2 is where the Dotstar strips connect to the board. The data & clock signals come from the microchip while the power connections come from the power circuit.

J3 & J4 are optional connectors that ease programming & development. J3 is a FTDI Serial connection that can be used to preview/sample different colors with our color testing firmware. J4 is an ISP connector that allows you to re-program the microchip without having to pull it out of it's socket.

Power

The power circuit uses a LM2576TV-5G switching voltage regulator to step down the battery voltage to 5V. It can pump out a maximum of 3 Amps, which is used to power the microcontroller & the LEDs.

The circuit design is derived from the voltage regulator's datasheet. C1 & C2 should be low-ESR capacitors rated for at least 16V(with a minimum ESR of 50 milliOhms for C2). C2 can be anywhere from 1000 to 2000 uF. L1 must be an inductor rated for at least 3 amps, going slightly over that is encouraged. D1 should be rated for 20V.

Microcontroller

The microcontroller circuit is mostly just connections to the other circuits.

Bypass capacitors are used on the connection to the power circuit. C3 & C4 are optional but C5, the 100nF capacitor, should always be included. The analog reference & power pins are connected to the power supply even though they are not used - this is recommended in the ATmega datasheet.

Crystal Oscillator

The oscillator circuit is pretty fluid. You can use a different frequency crystal(with a maximum of 20Mhz), or leave out the entire circuit and use the ATmega's 8Mhz internal oscillator instead. If you do modify the circuit, make sure your microcontroller's fuses are correctly programmed for your desired clock source and change the definition of the F_CPU macro in the firmware's Makefile to your new frequency.

Button

The main button is SW1. It is used to ignite/extinguish the saber & cycle through the programmed patterns. We've included both a tactile switch for development and an external connection so you can put your board in a hilt.

The reset button, SW2, is optional but ocassionally useful for testing & development.

Required Materials

Equipment

You'll want to have the following equipment/supplies:

• 22AWG Solid Hookup Wire
• AVR Programmer(like the USBtinyISP)
• Wire Strippers
• Flush Cutters
• Soldering Iron & Solder
• PCB Holder(optional)
• Anti-static Bracelet or ESD-safe Tweezers(optional)

If you're only testing this out on a breadboard you can get away with just:

• Breadboard
• Wire & Strippers
• AVR Programmer
• 5V Power Supply

Components

For the breadboard, you just need a Dotstar strip, an ATmega168a microcontroller & a tactile button.

For the prototyping board, you will need the following:

Part	Description	Link
	22x27 through-hole prototyping board	Amazon
BAT	7.4v Li-Ion battery	TCSS
LED	DotStar Strip, 144/m	Mouser
J1	2-pin JST connector	TCSS
J2	4-pin, 2.54mm pitch male header	Amazon
J3	6-pin, 2.54mm pitch male header	Amazon
J4	2x3-pin, 2.54mm pitch male header	Amazon
C1	100uF low-ESR electrolytic capacitor	Mouser
C2	1000-2000uF low-ESR electrolytic capacitor	Mouser
C3	10uF capacitor	Amazon(assorted)
C4	1uF capacitor	Amazon(assorted)
C5	100nF capacitor	Amazon(assorted)
C6, C7	20pF capacitor	Mouser
D1	3A, 20V Schottky Diode	Mouser
L1	47uH, 3A Fixed Inductor	Mouser
Y1	16Mhz Crystal	Mouser
SW1, SW2	6mm SPST OFF-(ON) tactile switch	Mouser
U1	LM2576TV-5G - 5V, 3A switching voltage regulator	Mouser
U2	28-pin DIP IC socket	Amazon
U2	Atmel ATmega168A-PU - AVR microcontroller	Mouser

For the circuit board, you will need SMD components instead:

Part	Description	Link
	RaveSaber v3.0.0 PCB	OSHPark
BAT	7.4v Li-Ion battery	TCSS
LED	DotStar Strip, 144/m	Mouser
J1	2-pin JST connector	TCSS
J2	4-pin, 2.54mm pitch male header	Mouser
J3	6-pin, 2.54mm pitch male header	Mouser
J4	2x3-pin, 2.54mm pitch male header	Mouser
J5	2-pin JST connector	TCSS
C1	100uF low-ESR electrolytic capacitor	Mouser
C2	1500uF low-ESR electrolytic capacitor	Mouser
C3	10uF capacitor	Mouser
C4	1uF capacitor	Mouser
C5	100nF capacitor	Mouser
C6, C7	20pF capacitor	Mouser
D1	3A, 20V Schottky Diode	Mouser
L1	47uH, 3A Fixed Inductor	Mouser
Y1	20Mhz Crystal	Mouser
SW1, SW2	4.5mm SPST OFF-(ON) tactile switch	Mouser
U1	LM2576TV-5G - 5V, 3A switching voltage regulator	Mouser
U2	28-pin DIP IC Socket	Mouser
U2	Atmel ATmega168A-PU - AVR microcontroller	Mouser

NOTE: The 4- & 6-pin headers link to a 20-pin header. We simply break this into the sizes necessary with some pliers.

NOTE: The DIP socket for U2 is machine-holed. You may prefer a leaf-spring socket instead.

Setup

Breadboard

A breadboard can be used for simple testing of colors/patterns as well as flashing the microchip with new firmware. You could use a smaller breadboard for the saber instead of a prototyping board, but it's not nearly as durable. Be wary of drawing too much current through your breadboard - you might melt it! Initial attempts used batteries and voltage regulation with the breadboard, but these instructions will assume you are running everything off a 5V bench power supply.

1. Place the ATmega168a chip in the center of the breadboard.
2. Connect the switch to ground and pin 4(PD2/INT0) of the microchip.
3. Connect pin 19(SCK) to the Dotstar strip's clock pin & pin 17(MOSI) to the strip's data pin.
4. Connect your power supply's 5V & ground leads to the microchip & Dotstar strip.

You should now be able to connect the GND, SCK, MOSI, MISO, & RESET pins of your programmer and flash your chip with the RaveSaber Firmware. Leave the VCC pin on your programmer unconnected since power is coming from your bench supply.

Prototyping Board

A prototyping board is the recommended way to setup v2.0.0 of the RaveSaber hardware.

The prototyping board is assembled by placing components and bridging pads with component leads, solder bridges, & wire. We've ommited C4, the 1uF decoupling capacitor but feel free to add it in.

First we place the components and make what connections we can with the component leads:

1. Start by placing the capacitors on the board and bending the leads so they stay on the board when you flip it over. You can also tack them into place with a small amount of solder.
2. Place the switches and voltage regulator. These should fit tight enough that they don't fall out when you flip the board over. If they do, tack them into place with some solder on the pins.
3. Place the DIP socket for U2 and tack it into place by soldering some of the unused pins.
4. Connect C1 and U1 by bending the leads of C1 and soldering them together.
5. Bridge GND & ON/OFF of U1 together. This keeps the regulator always running.
6. Place and solder L1. Bend & solder the positive lead of C2 to connect the two.
7. Since the leads of D1 are too thick for the board's holes, bend them down the board and solder each one over multiple pads.
8. Connect and solder the negative leads of C2, C3, C5, & SW2. Do the same with the positive leads of C3 & C5.
9. Use spare lead cuttings to bridge all the ground pins of SW1 & SW2 together. Bridge the top pins of each switch together as well, keeping the tops of SW1 & SW2 unconnected.
10. Place & solder Y1. Use the right leads of C6 & C7 to connect & solder them to the crystal and then to the proper DIP-socket pins.
11. Place and solder the J2, J3, & J4 headers. Use just enough solder to get them to hold into place - it'll make their wire connections easier to solder.
12. Bridge the ground pins of the serial & LED headers together. Leave space for the ground wire between C2 and the LED header.

Everything should now be on the board & the remaining connections can be made with your 22-gauge wire. We did this in the following order:

1. U1 to L1, D1, & C2.
2. C3 positive lead to C2.
3. C5 to VCC & GND of U2.
4. U2 second GND(pin 22) to SW1.
5. RESET from U2 to SW2.
6. BTN from U2 to SW1.
7. TXD from U2 to RXD of the serial header, followed by RXD to TXD.
8. RESET from U2 to the ISP header.
9. C2 to VCC & GND of the LED header.
10. GND from C2 to C6, C7, & the ISP header.
11. MOSI & SCK from U2 to the LED header.
12. MOSI, MISO, SCK from U2 to the LED header.
13. Connect two wires to C1 and terminate them with the JST connector.

Everything should be connected, your circuit should resemble the schematics, & your prototyping board should resemble the above layout.

Place the ATmega168a into the DIP socket at U2 & connect your Programmer's ISP cable and the battery. Flash the RaveSaber Firmware & disconnect the programmer & battery.

PCB Assembly

You should be decent at soldering SMD components before attempting this.

We recommend soldering C3 through C7 first, followed by U2, SW1, Y1, SW2, J2 through J4, D1, C1, L1, C2, & finally U2. Use female JST cables for J1 & J5. Scrub with isopropyl alcohol to clean off any flux.

You can now insert & flash the microchip, plug in the battery, connect the lights, and long-press SW1 to extend the blade.

Saber Blade / Hilt

The saber blade & hilt construction is very simple - we haven't put together a blade or hilt yet so we just attach our LEDs & protoboard to a piece of wood. We used a long 1x2 that we cut down after assembly. It's heavy, but you can actually swing it around.

1. Lay your DotStar strip at the end of your board & secure it with 4-5 zipties. Start at the far end, keeping the strip flat as you work towards the center of your wood.
2. Place the prototyping board below the strip, secure it with zipties at both ends and one in the center.
3. Flip the board over and place your battery near the board & strip, secure it with 3 zipties.
4. Connect the LED strip to the 4-pin header on the board and connect your battery to the board's JST connector.

You should now be able to long-press the button to illumunate the blade then short-press to switch patterns or long-press again to power down the blade.

TODO

• Auto-generate BOM(using KiBoM?)
  • Make sure to add DIP socket, LED strips, etc. to BoM
• Blade construction guide, using TCSS blade parts
• PVC Hilt construction guide
  • Eventually use MHS hilts as well, but that's not open hardware
  • See how much it'd cost to get someone to design an open/free metal hilt that machinists could reproduce.
  • Chassis disk design, for use w/ acrylic laser cutting service or online machine shop.
• Contact Saber design
  • For doing moves like this
  • Needs to be well balanced - some kind of chassis weighting?
  • Research best balance point for contact sabering
• Recharge port? Recharging blade stub?

Future Milestones

Rough drafts of future plans

• v3.1.0 - 90deg ISP pins? Source single component for all 1-row pins & have assembler break apart. blade build + guide
• v4.0.0 - pcb & chassis that fits in MHS hilts

References

Hilts

• Jay-gon's PVC Hilt Tutorial

Blades

• Neopixel Blade Assembly - FX-Sabers
• LED Blade Assembly

License

CERN OHL v1.2