adding legacy DIU and PIU schematic and Gerber PDFs

Documentation/legacy/README.md

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+"Legacy" RideLogic Data Files
+===
+
+These are the schematics and Gerber artwork for the driver interface unit (DIU)
+and the passenger interface unit (PIU).
+
+| File | Description |
+|------|-------------|
+| [driver-schematic.pdf](driver-schematic.pdf) | Driver Interface Unit (DIU) schematic |
+| [driver-artwork.pdf](driver-artwork.pdf) | Driver Interface Unit (DIU) Gerber artwork |
+| [rider-schematic.pdf](rider-schematic.pdf) | Passenger Interface Unit (PIU) schematic |
+| [rider-artwork.pdf](rider-artwork.pdf) | Passenger Interface Unit (PIU) Gerber artwork |
+
+DIU Notes
+---
+
+* PIC32MX360F (U6) running at 8MHz from an external oscillator
+* 7-segment clock:
+  - PIC talks to STP08DP05 (U9) shift register through (LED0, LED1, LED2, LED3)
+  - shift register only drives on digit at a time
+  - PIC multiplexes four digits on 7-segment clock with (LED4, LED5, LED6, LED7)
+* Viper serial connections through J19 (20x2 header)
+* Main power connector through J21
+  - (TX3,RX3) goes to PIU serial line
+  - (Vault0,Vault1) lines control vault motor through U12
+  - (DSR4,RTS4,CTS4) control GPRS modem
+  - (VIN) to GPRS and PIU
+* (J9) GPS connector
+  - Takes in (protected) bus power (VIN)
+  - Uses RS232 levels and feeds into (U8) - [R2IN,T2OUT]
+* GPS level converter (U8) SP3232EEN
+  - Takes in GPS levels to convert to PIC (GPSTTLRX, GPSTTLTX)
+  - Takes in PIC levels and converts to Viper serial levels (VIPTTLRX, VIPTTLTX) -> (RX2, TX2)
+* Debug serial line (J22) to get access to (RX1,TX1) on viper
+* Connector (J26) to potentiometers for sound, screen brightness and audio level
+  - (LEDADJ0,LEDADJ1) for 7-segment clock adjustment which feeds into (U9) to do brightness control
+  - (AN11) for LCD brightness control which feeds into PIC (that then pwm controls (BLAdj))
+
+
+License
+---
+
+All files in this directory are under a [CC0](https://creativecommons.org/share-your-work/public-domain/cc0/) license.
+
+![cc0](img/cc0_88x31.png)
+
+