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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.
+# Raspberry Pi Extension board
+
+A custom PLC-like system based on the Raspberry Pi.
+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.
+
+The project is intended for versatile use in prototyping and project development.
+
+
---
-# Notes
-## interface-board issues noticed when soldering
-- [x] digital in TVS diode footprint: dia is larger -> rotate one/space + 1.5mm drill
-- [x] make diodes pwm larger hole
-- [x] make pitch buzzer larger
--
-
-## interface-board issues at first test
-- analog leds vs terminal: CH0 and CH1 swapped (first, second terminal)
--> renamed nets and added notes
-- analog leds vs terminal: CH2 and CH3 swapped (third fourth terminal)
--
-- CH1 and CH7 led on
+### Photo of all hardware components
+
+ 
+
-## Power supply board
-FIXME: barrel-connector wrong polarity
--> change housing (connected via wires)
--> fix layout, schematic
+---
-
-# RPI Specs (Zero, 3+)
-- Available (old) Pi: Raspberry Pi 2 Model B v1.1
-- GPIO
- - Low: 0.9V
- - High: 1.6V
- - Input current: 5uA
- - Input capacitance: 5pF
- - Output Current +-17mA
- - Pullup / Pulldown 50-65k
-- EEPROM GPIO0 GPIO1, leave unused
+# Repository Content
+- **KiCad Projects**: 3 KiCad projects with schematics and PCB layouts for the custom pcbs created.
+- **Housing**: Custom enclosure design for PCBs and Raspberry Pi created in FreeCAD.
+- **Software/Firmware**: Python scripts for operating and testing the PCB features (WIP).
-
-# Feature Ideas
-- [x] Temperature control
- - fan
- - auto turn on
- - temp sensor
- - ~~turn on via gpio~~
+---
-## Supply
-- Input protection
- - [x] TVS
- - [x] reverse polarity (polyfuse will trigger)
- - [x] Fuse (5A polyfuse)
- - [x] buffer
-- [x] Pass through power supply
-- [x] 3.3V, 5V, 12V, 24V Regulator
+# Features Overview
+This project provides:
+- Protected GPIO I/O for Raspberry Pi.
+- Various analog inputs
+- Flexible power supply options. (3.3 V, 5 V, -5 V, 12 V, 24 V outputs)
+- Relay and MOSFET control.
+- Integrated LEDs for status indication.
+- RS485, I2C, SPI, and UART bus communication.
-- [x] power by barrel connector (24V 5A)
-- ~~power by usb~~ [not allowed]
- - ~~Switch between power by USB or power supply?~~
-- ~~power by battery~~ [dropped]
- - liion cell connector
- - BMS / charge controller
- - measure battery voltage
- - USB charging port
+Detailed features of each PCB are described in the respective sections below.
+
+---
+
+# Designed PCBs
+
+## 1. **Raspberry Pi Interface Board**
+This board connects to the Raspberry Pi via a 40-pin ribbon cable and provides protected GPIO extensions and versatile input/output features.
+
+### Photo
+
+
+### Features
+**Inputs**:
+- **8x Digital Inputs**:
+ - Wide continous voltage range (-1.7V to 120V), idea: compatible with 3V and 24V devices.
+ - TVS diodes for ESD and spike protection.
+ - Reverse polarity protection
+ - Isolated with optocouplers.
+ - Optional low-pass filters (toggle via DIP switches).
+
+- **8x Analog Inputs
+ - Different fixed range inputs:
+ - 2x 0 - 3.3 V
+ - 2x 0 - 5 V
+ - 1x 0 - 12 V
+ - 1x 0 - 24 V
+ - 2x 0 - 20 mA
+ - Overvoltage protection with clamping diodes.
+ - Optional low-pass filters (toggle via DIP switches).
+
+**Outputs**:
+- 1x onboard buzzer.
+- 2x 16A relays.
+- 2x high-power MOSFETs (N-channel, max 55V, 33A continuous, 160A pulsed).
+- 8x digital outputs (via shift register):
+ - Low-power (30mA push-pull) and high-power (500mA open-drain) outputs.
+ - Buzzer and relays connected to channels 6-8, with enable/disable switches.
+ - Note: Outputs are **not short-circuit proof**.
+
+**General**:
+- WAGO spring-loaded terminals for easy wiring.
+- JST connectors for external LEDs for all inputs and outputs indicate the current pin state.
+
+**Bus Communication**:
+- RS485 (TVS protection, idle pullup/pulldown, 120Ω terminator).
+- UART (unprotected).
+- I2C (TVS diodes, 2.2k pullups).
+- SPI (unprotected).
+Note: Either RS485 or UART can be used at the same time (select with jumpers)
+
+### Schematic and Layout
+
+
+ 
+
+ 
+
-## IO
-- Input
- - GPIO
- - [x] wide voltage range (-1.7 to 120V)
- - [x] TVS
- - [x] reverse polarity (-1.73V max)
- - [x] Low pass filter
- - [x] Optocoupler input
- - [x] ADC
- - external IC
- - ~~multiplexer?~~
- - protection
- - scale input voltage
- - fixed inputs: 24V 12V 5V 3.3V
- - 20mA input
- - ~~trim potentiometer?~~
-- Output
- - [x] Relay
- - [x] Mosfet
- - [x] Optocoupler output
- - [ ] GPIO with over current protection
- - [ ] GPIO level shift (24V output)
- - [x] PWM pins
- - [x] shift register
- - [ ] DAC
-
-- [x] LEDS indicate I/O state
-- [ ] Testpoints
-- [x] ESD protection (tvs diodes uart, i2c...)
+---
-## Bus
-- [x] UART/RS485
-- [ ] RS232 Connector
-- [x] I2C Pullup
-- [x] SPI
-- [ ] CAN
-- ~~Serial to usb (if Arduino)~~
-- ~~OWB default GPIO4~~
+## 2. **Power Supply Board**
+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)
+
+### Photo
+
+
+### Features
+**Input**:
+- 24V 5A barrel plug.
+- 5A self-resetting polyfuse.
+- Reverse polarity protection.
+
+**Output**:
+- 3.3V, 3A (buck converter).
+- 5V, 5A (buck converter).
+- -5V, 20mA (charge pump).
+- 12V, 3A (buck converter).
+- 24V (supply voltage filtered).
+
+**Fan Control:**
+- 2x connector for 10k NTC.
+- Threshold adjustable (trim poti).
+- Hysteresis adjustable (trim poti).
+- select between 5V or 12V Fan.
+
+**General**:
+- Spring-loaded terminals for each voltage.
+- Combined internal terminals for all voltages.
+
+### Schematic and Layout
+
+
+ 
+
+ 
+
+
+---
+
+## 3. **LED Boards**
+Small PCBs with LEDs, resistors, and mounting holes for housing indicators.
+
+### Photo
+
+
+### Boards
+1. 2x 5mm LEDs for relays.
+2. 2x 5mm LEDs for PWM outputs.
+3. 8x 3mm yellow LEDs for analog inputs.
+4. 8x 3mm orange LEDs for digital inputs.
+5. 8x 3mm red LEDs for digital outputs.
+
+### Schematic and Layout
+
+
+ 
+
+ 
+
-## UI
-- Input [dropped]
- - Buttons
- - DIP switches?
- - Temperature sensor
- - Encoder
- - Potentiometer
-- Output
- - [ ] Display [RPI display pending]
- - [x] Buzzer
- - [x] LEDS
+---
-## Mechanical
-- [x] Barrel plug (24V 3A supply)
-- ~~Screw terminals~~
-- [x] spring loaded?
-- ~~pass through all pins?~~
-
-## Housing
-- RPI ports
-- banana sockets for power out
-- screw terminal exposed
-- buttons, leds: need to open up?
-- BNC? []
+# Software/Firmware
+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.
-## Other
-- Extension board with multiplexer
-- Breadboard compatible?
-- SD Card
-- ~~Onboard MCU for standalone use?~~
-- ~~separate bought MCU via i2c for additional GPIO, DAC, ADC in one~~
+---
-## Questions
-- what analog input ranges (Voltage, Count)
-- RS232 RS485 SPI, IIC actually necessary? examples
-- CAN to second SPI?
-- 8x shift register outputs, 0.5A open drain or 7mA tristate
-- 2x PWM 30A enough?
-- max used PWM freq? (drop opto if >80khz)
\ No newline at end of file
+# Housing
+Custom-designed enclosure includes:
+- Ports for Raspberry Pi.
+- Banana sockets for power outputs.
+- Exposed screw terminals.
+- Openings for buttons and LEDs.
+- Mounts for all PCBs and wiring.
+
+
+
+
+---
+
+
+# Dropped Features
+The following ideas were considered but not implemented:
+- UI Input Elements:
+ - Buttons, DIP switches, temperature sensors, encoders, or potentiometers.
+- USB or battery-powered operation:
+ - Battery packs with BMS and voltage measurement.
+- Li-ion cell holders.
+
+---