REWORK README WIP
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README.md
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README.md
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A Raspberry Pi-compatible PCB that extends the GPIO header with protected I/O, relays, and various features for versatile use in prototyping and project development.
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# Raspberry Pi Extension board
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A custom PLC-like system based on the Raspberry Pi.
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With a custom interface board a raspberry pi is extended with protected I/O, bus systems, analog inputs and Relay or PWM outputs. All components including a display are housed in a custom designed enclosure.
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The project is intended for versatile use in prototyping and project development.
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---
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---
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# Notes
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## interface-board issues noticed when soldering
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### Photo of all hardware components
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- [x] digital in TVS diode footprint: dia is larger -> rotate one/space + 1.5mm drill
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<p align="center">
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- [x] make diodes pwm larger hole
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<img src="doc/photos/all-components.jpg" alt="All Components (Disassembled)" width="75%"/>
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- [x] make pitch buzzer larger
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</p>
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-
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## interface-board issues at first test
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- analog leds vs terminal: CH0 and CH1 swapped (first, second terminal)
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-> renamed nets and added notes
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- analog leds vs terminal: CH2 and CH3 swapped (third fourth terminal)
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-
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- CH1 and CH7 led on
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## Power supply board
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---
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FIXME: barrel-connector wrong polarity
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-> change housing (connected via wires)
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-> fix layout, schematic
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# Repository Content
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# RPI Specs (Zero, 3+)
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- **KiCad Projects**: 3 KiCad projects with schematics and PCB layouts for the custom pcbs created.
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- Available (old) Pi: Raspberry Pi 2 Model B v1.1
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- **Housing**: Custom enclosure design for PCBs and Raspberry Pi created in FreeCAD.
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- GPIO
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- **Software/Firmware**: Python scripts for operating and testing the PCB features (WIP).
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- Low: 0.9V
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- High: 1.6V
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- Input current: 5uA
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- Input capacitance: 5pF
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- Output Current +-17mA
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- Pullup / Pulldown 50-65k
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- EEPROM GPIO0 GPIO1, leave unused
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---
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# Feature Ideas
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- [x] Temperature control
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- fan
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- auto turn on
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- temp sensor
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- ~~turn on via gpio~~
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## Supply
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# Features Overview
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- Input protection
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This project provides:
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- [x] TVS
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- Protected GPIO I/O for Raspberry Pi.
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- [x] reverse polarity (polyfuse will trigger)
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- Various analog inputs
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- [x] Fuse (5A polyfuse)
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- Flexible power supply options. (3.3 V, 5 V, -5 V, 12 V, 24 V outputs)
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- [x] buffer
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- Relay and MOSFET control.
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- [x] Pass through power supply
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- Integrated LEDs for status indication.
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- [x] 3.3V, 5V, 12V, 24V Regulator
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- RS485, I2C, SPI, and UART bus communication.
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- [x] power by barrel connector (24V 5A)
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Detailed features of each PCB are described in the respective sections below.
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- ~~power by usb~~ [not allowed]
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- ~~Switch between power by USB or power supply?~~
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---
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- ~~power by battery~~ [dropped]
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- liion cell connector
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# Designed PCBs
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- BMS / charge controller
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- measure battery voltage
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## 1. **Raspberry Pi Interface Board**
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- USB charging port
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This board connects to the Raspberry Pi via a 40-pin ribbon cable and provides protected GPIO extensions and versatile input/output features.
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### Photo
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<img src="doc/photos/rpi-interface-board.jpg" alt="Raspberry Pi Interface Board" width="60%"/>
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### Features
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**Inputs**:
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- **8x Digital Inputs**:
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- Wide continous voltage range (-1.7V to 120V), idea: compatible with 3V and 24V devices.
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- TVS diodes for ESD and spike protection.
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- Reverse polarity protection
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- Isolated with optocouplers.
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- Optional low-pass filters (toggle via DIP switches).
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- **8x Analog Inputs
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- Different fixed range inputs:
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- 2x 0 - 3.3 V
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- 2x 0 - 5 V
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- 1x 0 - 12 V
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- 1x 0 - 24 V
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- 2x 0 - 20 mA
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- Overvoltage protection with clamping diodes.
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- Optional low-pass filters (toggle via DIP switches).
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**Outputs**:
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- 1x onboard buzzer.
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- 2x 16A relays.
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- 2x high-power MOSFETs (N-channel, max 55V, 33A continuous, 160A pulsed).
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- 8x digital outputs (via shift register):
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- Low-power (30mA push-pull) and high-power (500mA open-drain) outputs.
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- Buzzer and relays connected to channels 6-8, with enable/disable switches.
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- Note: Outputs are **not short-circuit proof**.
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**General**:
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- WAGO spring-loaded terminals for easy wiring.
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- JST connectors for external LEDs for all inputs and outputs indicate the current pin state.
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**Bus Communication**:
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- RS485 (TVS protection, idle pullup/pulldown, 120Ω terminator).
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- UART (unprotected).
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- I2C (TVS diodes, 2.2k pullups).
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- SPI (unprotected).
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Note: Either RS485 or UART can be used at the same time (select with jumpers)
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### Schematic and Layout
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<p align="center">
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<a href="pi-interface-board_v1.0/export/schematic_interface-board.pdf">
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<img src="pi-interface-board_v1.0/export/schematic_interface-board.svg" width="49%" alt="Schematic"/>
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</a>
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<img src="pi-interface-board_v1.0/export/layout_interface-board.png" width="49%" alt="PCB Layout"/>
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</p>
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## IO
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---
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- Input
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- GPIO
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- [x] wide voltage range (-1.7 to 120V)
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- [x] TVS
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- [x] reverse polarity (-1.73V max)
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- [x] Low pass filter
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- [x] Optocoupler input
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- [x] ADC
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- external IC
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- ~~multiplexer?~~
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- protection
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- scale input voltage
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- fixed inputs: 24V 12V 5V 3.3V
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- 20mA input
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- ~~trim potentiometer?~~
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- Output
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- [x] Relay
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- [x] Mosfet
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- [x] Optocoupler output
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- [ ] GPIO with over current protection
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- [ ] GPIO level shift (24V output)
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- [x] PWM pins
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- [x] shift register
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- [ ] DAC
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- [x] LEDS indicate I/O state
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- [ ] Testpoints
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- [x] ESD protection (tvs diodes uart, i2c...)
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## Bus
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## 2. **Power Supply Board**
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- [x] UART/RS485
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Creates different voltages from supplied 24V. Supply for the rpi interface board as well as several terminals for variable use (connect sensors, devices etc to the housing)
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- [ ] RS232 Connector
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- [x] I2C Pullup
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### Photo
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- [x] SPI
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<img src="doc/photos/power-supply-board.jpg" alt="Power Supply Board" width="50%"/>
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- [ ] CAN
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- ~~Serial to usb (if Arduino)~~
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### Features
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- ~~OWB default GPIO4~~
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**Input**:
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- 24V 5A barrel plug.
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- 5A self-resetting polyfuse.
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- Reverse polarity protection.
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**Output**:
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- 3.3V, 3A (buck converter).
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- 5V, 5A (buck converter).
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- -5V, 20mA (charge pump).
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- 12V, 3A (buck converter).
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- 24V (supply voltage filtered).
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**Fan Control:**
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- 2x connector for 10k NTC.
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- Threshold adjustable (trim poti).
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- Hysteresis adjustable (trim poti).
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- select between 5V or 12V Fan.
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**General**:
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- Spring-loaded terminals for each voltage.
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- Combined internal terminals for all voltages.
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### Schematic and Layout
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<p align="center">
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<a href="power-supply-board_v1.0/export/schematic_power-supply.pdf">
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<img src="power-supply-board_v1.0/export/schematic_power-supply.svg" width="55%" alt="Schematic"/>
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</a>
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<img src="power-supply-board_v1.0/export/layout_power-supply.png" width="44%" alt="PCB Layout"/>
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</p>
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---
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## 3. **LED Boards**
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Small PCBs with LEDs, resistors, and mounting holes for housing indicators.
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### Photo
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<img src="doc/photos/led-boards.jpg" alt="LED Boards" width="60%"/>
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### Boards
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1. 2x 5mm LEDs for relays.
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2. 2x 5mm LEDs for PWM outputs.
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3. 8x 3mm yellow LEDs for analog inputs.
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4. 8x 3mm orange LEDs for digital inputs.
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5. 8x 3mm red LEDs for digital outputs.
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### Schematic and Layout
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<p align="center">
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<a href="led-boards_v0.1/export/schematic_led-boards.pdf">
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<img src="led-boards_v0.1/export/schematic_led-boards.svg" width="48%" alt="Schematic"/>
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</a>
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<img src="led-boards_v0.1/export/layout_led-boards.png" width="51%" alt="PCB Layout"/>
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</p>
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## UI
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- Input [dropped]
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- Buttons
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- DIP switches?
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- Temperature sensor
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- Encoder
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- Potentiometer
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- Output
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- [ ] Display [RPI display pending]
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- [x] Buzzer
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- [x] LEDS
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## Mechanical
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# Software/Firmware
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- [x] Barrel plug (24V 3A supply)
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Python code for operating the extension PCBs (e.g., GPIO pins, shift registers, ADC, and bus communication). This section is a work in progress (WIP), and example scripts will be added as development continues.
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- ~~Screw terminals~~
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- [x] spring loaded?
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- ~~pass through all pins?~~
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## Housing
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- RPI ports
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- banana sockets for power out
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- screw terminal exposed
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- buttons, leds: need to open up?
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- BNC? []
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## Other
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- Extension board with multiplexer
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- Breadboard compatible?
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- SD Card
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- ~~Onboard MCU for standalone use?~~
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- ~~separate bought MCU via i2c for additional GPIO, DAC, ADC in one~~
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## Questions
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# Housing
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- what analog input ranges (Voltage, Count)
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Custom-designed enclosure includes:
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- RS232 RS485 SPI, IIC actually necessary? examples
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- Ports for Raspberry Pi.
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- CAN to second SPI?
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- Banana sockets for power outputs.
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- 8x shift register outputs, 0.5A open drain or 7mA tristate
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- Exposed screw terminals.
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- 2x PWM 30A enough?
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- Openings for buttons and LEDs.
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- max used PWM freq? (drop opto if >80khz)
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- Mounts for all PCBs and wiring.
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<img src="doc/images/3d-model_housing.png" width="51%" alt="3d-model"/>
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# Dropped Features
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The following ideas were considered but not implemented:
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- UI Input Elements:
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- Buttons, DIP switches, temperature sensors, encoders, or potentiometers.
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- USB or battery-powered operation:
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- Battery packs with BMS and voltage measurement.
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- Li-ion cell holders.
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---
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