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doc/devices/PCB-K0402W-V1.0.md

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+# PCB-K0402WS-V1.0
+
+This is the first revision of the PCB-K0402WS series of boards; it's very similar to 2.0 in terms of layout/wiring.
+
+The board does have footprints for a VLAN modeswitch at the front and a second flash chip on the bottom of the PCB, but these have been seen to ship unpopulated.
+
+### Brands
+
+* YuanLey YS25-0402 <sup><sub>Note: there are [multiple revisions](PCB-K0402W-V3.0.md) of the YS25-0402. This first revision lacks the "Vlan" switch cutout on the front of the enclosure.</sub></sup>
+
+### Programming
+
+Use a SOIC-8 clamp to the flash chip (U1 on silkscreen) at the top of the board, leaving it otherwise unpowered.
+
+The board has been seen to ship with a single [BoyaMicro BY25Q16BSSIG](https://www.lcsc.com/datasheet/C382744.pdf) 16Mbit (2MiB) chip, though exact BOM may vary.
+
+<a href="photos/PCB-K0402W-V1.0/flash.jpg"><img src="photos/PCB-K0402W-V1.0/flash.jpg" width="300" /></a>
+
+### What works
+
+- All four 2.5GBASE-T RJ45 ports at 10/100/1000/2500 Mbps
+- Both SFP ports supporting 1G, 2.5G and 10G modules
+- LEDs (Power LED is always on)
+
+### PCB overview
+
+#### Board markings
+- Top silkscreen: PCB-K0402W-V1.0 / DIP-K0402WS-V1.0
+
+#### Key components
+- U1: SPI NOR flash, 2 MiB
+- S1: unpopulated slide switch footprint (three through-holes used as serial console)
+
+Front panel
+
+<a href="photos/PCB-K0402W-V1.0/ports.jpg"><img src="photos/PCB-K0402W-V1.0/ports.jpg" width="300" /></a>
+
+PCB top
+
+<a href="photos/PCB-K0402W-V1.0/pcb-top.jpg"><img src="photos/PCB-K0402W-V1.0/pcb-top.jpg" width="300" /></a>
+
+PCB bottom
+
+<a href="photos/PCB-K0402W-V1.0/pcb-bottom.jpg"><img src="photos/PCB-K0402W-V1.0/pcb-bottom.jpg" width="300" /></a>
+
+Bottom and rear
+
+<a href="photos/PCB-K0402W-V1.0/bottom.jpg"><img src="photos/PCB-K0402W-V1.0/bottom.jpg" width="300" /></a>
+
+### Power supply
+
+Input power is delivered via a standard DC barrel jack (5.5x2.1mm) with an included 12V 1A adapter.
+
+There is an optional grounding screw next to the DC input.
+
+### Serial console
+
+The PCB has a slide switch footprint (unpopulated) at the front right that is connected to the UART. It is labeled as "S1" on the silkscreen.
+
+Facing the top front (port) side of the board, the pinout from left to right is:
+
+| Position | Signal | GPIO              |
+|----------|--------|-------------------|
+| 1        | RX     | GPIO32\_UART0\_RX |
+| 2        | GND    | N/A               |
+| 3        | TX     | GPIO31\_UART0\_TX |
+
+Standard 0.1" / 2.54mm pin headers will not fit, so wires or clips may be used instead.
+
+The image below shows some oversized clips clumsily attached.
+
+<a href="photos/PCB-K0402W-V1.0/uart.jpg"><img src="photos/PCB-K0402W-V1.0/uart.jpg" width="300" /></a>