Xevelabs Product Documentation

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===== USB2AX: Technical Specifications =====

The hardware of the USB2AX is relatively simple: only 17 components and a 16x20mm PCB.

{{product:usb2ax:USB2AXv31_front_euro_s.jpg}}

At its core is an ATMega32u2, an USB-enabled 8bit MCU with 32KB of FLASH, 1KB of RAM and 1KB of EEPROM, running at 16MHz.

The USB2AX v3.1 has a double LED (Red/Green), ESD protection on both connectors (USB and serial), 0.1" breakout pads for RST, GND, HWB and the 4 SPI pins (PB0 to PB3).


To achieve Half-duplex operation on DATA, TX and RX are shorted together and the firmware alternatively turns ON the transmission or reception side of the MCU's UART. This is inspired by the [[http://www.vanadiumlabs.com/arbotix.html|Arbotix]].

==== Schematics ====

{{product:usb2ax:usb2ax_v3.1_schematics.png}}\\
[[https://paranoidstudio.assembla.com/code/paranoidstudio/git/nodes/master/usb2ax/elec|All Eagle files]]

The protection circuitry for DATA, with the zener diode and PTC resistor, comes from the [[http://ruggedcircuits.com/html/ruggeduino.html|Ruggeduino]], and makes it possible to withstand applying 12V to DATA indefinitely. More detailed explanation of how it works [[http://forums.trossenrobotics.com/showthread.php?5675-USB2AX-v3.1&p=53101#post53101|here]]. This situation can easily happen in real life with a shoddy custom or damaged cable, and improper protection could result in a fried motherboard... 


==== Bill Of Material ====

^ #  ^ Ref. ^ Qty. ^ Description                                                 ^ Part Value ^     Package    ^
| 1  | U1    | 1 | ATMega32u2 MCU                                                | ATMEGA32U2-MU | QFN-32      |
| 2  | Q1    | 1 | SMD 16MHz quartz                                              | 16MHz | CRYSTAL-SMD-3.2X2.5 | 
| 3  | USB1  | 1 | USB Type A Plug through hole                                  |          | USB-A-THT        | 
| 4  | DXL1  | 1 | Dynamixel Connector Right Angle                               | SPOX2.5-3WAY                |
| 5  | C1    | 1 | USB decoupling capacitor                                      | 4.7µF    | C0603            | 
| 6  | C2,C3 | 2 | ATmega decoupling capacitors                                  | 0.1µF    | C0402            | 
| 7  | C4    | 1 | Capacitor for UCAP                                            | 1.0µF    | C0402            |
| 8  | C5,C6 | 2 | Load capacitor for quartz                                     | 18pF     | C0402            | 
| 9  | R1    | 1 | USB line resistor array                                       | 22R      | 0402x2           | 
| 10 | R3    | 2 | DATA line protection and current limiting resistor array for LEDs | 150R | 0402x2           | 
| 11 | RPTC1 | 1 | PTC resistor for DATA overvoltage protection                  | 100R     | C0603            | 
| 12 | D1    | 1 | Zener diode for DATA overvoltage protection                   | 5.1V     | SOD-923          | 
| 13 | LED1  | 1 | Double LED                                                    | Green/Red | C0603           | 
| 14 | U2    | 1 | ESD protection                                                |            | XSON6         | 
| 15 |       | 1 | Heat-shrink tubing (diam:12,7mm)(length:24mm+/-1mm)(TRANSPARENT) |            |  |

==== Mechanical ====

Size: 16mm x 36mm x ~7mm (without heat-shrink tubing)

[[http://www.xevel.fr/other/usb2ax_v3.1.stl|3D CAD file (stl)]]
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