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The hardware of the USB2AX is relatively simple: only 17 components and a 15x20mm PCB.
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 Arbotix.
The protection circuitry for DATA, with the zener diode and PTC resistor, comes from the Ruggeduino, and makes it possible to withstand applying 12V to DATA indefinitely. More detailed explanation of how it works 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…
|2||Q1||1||SMD 16MHz quartz||16MHz||CRYSTAL-SMD-3.2×2.5|
|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||0402×2|
|10||R3||2||DATA line protection and current limiting resistor array for LEDs||150R||0402×2|
|11||RPTC1||1||PTC resistor for DATA overvoltage protection||100R||C0603|
|12||D1||1||Zener diode for DATA overvoltage protection||5.1V||SOD-923|
|15||1||Heat-shrink tubing (diam:12,7mm)(length:24mm+/-1mm)(TRANSPARENT)|
Size: 16mm x 36mm x ~7mm (without heat-shrink tubing)