# 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.


---


## Photo of All Hardware Components
<p align="center">
  <img src="doc/photos/all-components.jpg" alt="All Components (Disassembled)" width="75%"/>
</p>


---


# 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 run on the Raspberry Pi for operating and testing the PCB features and providing examples as base for future projects.


---


# 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.

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
<img src="doc/photos/rpi-interface-board.jpg" alt="Raspberry Pi Interface Board" width="80%"/>

### Features
**Inputs**:
- **8x Digital Inputs**:
  - Wide voltage range (-1.7 V to 120 V) → compatible with 3 V and 24 V 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 16 A relays.
- 2x high-power MOSFETs (N-channel, max 55 V, 33 A continuous, 160 A pulsed).
- 8x digital outputs (via shift register):
  - Low-power (30 mA push-pull) and high-power (500 mA 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 to indicate the current pin state.

**Bus Communication**:
- RS485 (TVS protection, idle pull-up/pull-down, 120 Ω terminator).
- UART (unprotected).
- I2C (TVS diodes, 2.2 kΩ pull-ups).
- SPI (unprotected).
  - **Note**: RS485 and UART cannot be used simultaneously (select via jumpers).

### Schematic and Layout
<p align="center">
  <a href="pi-interface-board_v1.0/export/schematic_interface-board.pdf">
    <img src="pi-interface-board_v1.0/export/schematic_interface-board.svg" width="49%" alt="Schematic"/>
  </a>
  <img src="pi-interface-board_v1.0/export/layout_interface-board.png" width="49%" alt="PCB Layout"/>
</p>


---


## 2. **Power Supply Board**
Creates different voltages from supplied 24 V. Supply for the Raspberry Pi interface board as well as several terminals for variable use (connect sensors, devices, etc., to the housing).

### Photo
<img src="doc/photos/power-supply-board.jpg" alt="Power Supply Board" width="60%"/>

### Features
**Input**:
- 24 V 5 A barrel plug.
- 5 A self-resetting polyfuse.
- Reverse polarity protection.

**Output**:
- 3.3 V, 3 A (buck converter).
- 5 V, 5 A (buck converter).
- -5 V, 20 mA (charge pump).
- 12 V, 3 A (buck converter).
- 24 V (supply voltage filtered).

**Fan Control**:
- 2x connector for 10 kΩ NTC.
- Threshold adjustable (trimmer potentiometer).
- Hysteresis adjustable (trimmer potentiometer).
- Select between 5 V or 12 V fan.

**General**:
- Spring-loaded terminals for each voltage.
- Combined internal terminals for all voltages.

### Schematic and Layout
<p align="center">
  <a href="power-supply-board_v1.0/export/schematic_power-supply.pdf">
    <img src="power-supply-board_v1.0/export/schematic_power-supply.svg" width="55%" alt="Schematic"/>
  </a>
  <img src="power-supply-board_v1.0/export/layout_power-supply.png" width="44%" alt="PCB Layout"/>
</p>

---

## 3. **LED Boards**
Small PCBs with LEDs, resistors, and mounting holes for housing indicators.

### Photo
<img src="doc/photos/led-boards.jpg" alt="LED Boards" width="60%"/>

### Boards
1. 2x 5 mm LEDs for relays.
2. 2x 5 mm LEDs for PWM outputs.
3. 8x 3 mm yellow LEDs for analog inputs.
4. 8x 3 mm orange LEDs for digital inputs.
5. 8x 3 mm red LEDs for digital outputs.

### Schematic and Layout
<p align="center">
  <a href="led-boards_v0.1/export/schematic_led-boards.pdf">
    <img src="led-boards_v0.1/export/schematic_led-boards.svg" width="48%" alt="Schematic"/>
  </a>
  <img src="led-boards_v0.1/export/layout_led-boards.png" width="51%" alt="PCB Layout"/>
</p>


<br>

---

<br>

# Raspberry Pi Usage

## Connectivity
The Raspberry Pi can operate **standalone** with a connected keyboard, mouse, and HDMI monitor, or by using the integrated display in the housing.  

However, for **development**, it is recommended to connect it to a network via **WiFi or LAN**, allowing easy remote access from a laptop. A direct **Ethernet connection** between the Raspberry Pi and a laptop is often the simplest method.

### LAN Connection (Ethernet)
- **Connection**: Connect cable directly between raspberry and PC
- **Configure the PC interface**: Set a static ip address e.g. `192.168.1.1/24`  
  Note: Optionally also enable network sharing to enable the RPI to use the internet connection the PC currently has.
- **Configure the Raspberry Interface**: Set a static ip address e.g. `192.168.1.100/24`  
  The Raspberry Pi can be configured for **Ethernet access** using different methods:
  - **Boot Partition Configuration:** Modify `cmdline.txt` on the SD card.
  - **GUI Setup:** Use the built-in network manager if a monitor is connected.
  - **Command Line (`nmcli`)**: Configure networking via the terminal.  

To check the assigned IP run:
```bash
ip a
```

### WiFi Connection
Probably the **fastest and easiest** way to set up communication between the Raspberry Pi and a PC - while even maintaining internet access - is to **use a mobile phone as a WiFi hotspot**.  
Simply **connect both the Raspberry Pi and the laptop** to the same hotspot.

To connect to a WiFi network, use:
```bash
nmcli device wifi connect <SSID> password <password>
```
Replace `<SSID>` and `<password>` with the actual credentials.  
The Raspberry Pi will **automatically reconnect** after a reboot.  
 
Once connected, you can check the assigned IP on the Raspberry Pi using:
 ```
 ip a
 ```

### SSH Access
For remote terminal access, connect via SSH from a laptop:
```bash
ssh pi@192.168.1.100
```
Replace the IP with the actual address of the Raspberry Pi.

### Remote Desktop (RDP)
To control the Raspberry Pi’s **GUI remotely**, RDP is pre-configured.

#### Connect via Windows Remote Desktop:
- Open **Remote Desktop Connection (mstsc)**.
- Enter the Raspberry Pi’s IP address.
- **Login:**  
  - **User:** `root`  
  - **Password:** (configured during setup)  
  - **Note:** Logging in as `pi` may result in a black screen.

#### Alternatively, use PowerShell:
```powershell
mstsc /v:192.168.1.100:3389
```

### Mount Raspberry Pi Filesystem in Windows (SAMBA)
For convenient file access and editing (e.g., with **VS Code**), the Raspberry Pi’s `/home/pi` directory can be **mounted as a network drive** using Samba.

#### Steps:
1. Determine the Raspberry Pi’s IP address:
   ```bash
   ip a
   ```
2. Mount the `/home/pi` directory in Windows:
   ```powershell
   net use X: \\192.168.1.100\pi /user:pi
   ```
   Replace `192.168.1.100` with the actual IP address.

**Note:**  
Currently, only `/home/pi` is available for mounting. To share additional directories, edit the Samba configuration file:
```bash
# add a new `[share]` section with the desired folder path and permissions.
sudo nano /etc/samba/smb.conf
# then restart samba
sudo systemctl restart smbd
```


<br>

---

<br>


# Python Scripting
All **terminal-to-pin assignments** are mapped in [`interface_board_pins.py`](rpi-scripts/interface_board_pins.py), allowing easy reference to terminal numbers labeled on the housing.  

Example scripts demonstrating I/O control can be found in [`rpi-scripts/examples`](rpi-scripts/examples).

---

## Scripts & Development

### Running Python Examples
Pre-written **Python scripts** to control I/O terminals are located in:
```
rpi-scripts/examples
```
To run an example, execute:
```bash
cd /home/pi/git/rpi-interface-board/rpi-scripts/examples/
python read_digital_inputs.py
```

### Starting a New Python Project with I/O Access
To create a custom Python project using the **interface board**, follow these steps:

1. **Copy the entire `rpi-scripts/` folder** to your new project directory.
2. **Remove unnecessary files**, keeping at least:
   - `rpi-scripts/interface_board_libs/` → contains custom drivers.
   - `rpi-scripts/interface_board_pins.py` → maps terminal numbers to GPIO/ADC channels.
3. **Start coding** by modifying an existing example in `examples/`.

---

## GUI Interface
A **Python GUI** is available for **real-time monitoring** and **control** of all I/O terminals for quick testing.

### Run the GUI
```bash
cd rpi-scripts/gui
python main.py
```

### Enable GUI Autostart on Boot
The GUI is configured to start automatically on boot in **fullscreen mode**. To modify this behavior:

#### Enable autostart:
```bash
sudo cp rpi-scripts/gui/gui-start.service /etc/systemd/system/
sudo systemctl enable gui-start.service
```

#### Disable autostart:
```bash
sudo systemctl disable gui-start.service
```

### GUI Screenshots
<p align="center">
  <img src="doc/graphics/python-gui-control.png" width="80%" />
  <img src="doc/graphics/python-gui-monitor.png" width="80%" />
</p>


<br>

---

<br>


# Housing
Custom-designed enclosure includes:
- Cutouts for all Ports for Raspberry Pi.
- Mounting screws for all pcbs and Raspberry
- Fan mount + venting slots
- Cutouts for all external pcb terminals
- Cutout + mounting arms (M2.5) for Display
<img src="doc/graphics/3d-model_housing.png" width="80%" alt="3D Model"/>


---


# 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.
- Analog output (DAC)
- More bus systems
  - RS232 Interface
  - CAN Interface