flux

#Goal

- Design a compact RS485 node that integrates a low-power STM32 microcontroller, powered via 24 V over the same Cat5 cable used for RS485 communications, with three electrically driven mechanically bistable relays (rated 230 V / 16 A), three digital I/O inputs, and one DS18B20 temperature sensor. The node will safely interface high voltage loads with sensitive low-voltage logic while conforming to safety and size constraints.

#Implementation plan

1. **Project Definition & Documentation**

1. Update the project description to reflect the node's functional scope including power, communications, relay control, and sensor interfacing.

2. **Power Supply Subsystem**

1. Add a 24 V input port sourced from the Cat5 cable.

2. Design and add a buck converter/regulator to generate the required low-voltage rail (e.g., 3.3 V or 5 V) for the STM32 and peripheral circuitry.

3. **RS485 Communication Interface**

1. Select and add an RS485 transceiver component (e.g., MAX485 or equivalent) to the schematic.

2. Connect the transceiver to the UART pins of the STM32 MCU.

4. **STM32 Microcontroller Integration**

1. Select and add a compact STM32 microcontroller component from the Flux parts library.

2. Configure power and signal connections to support node operations.

5. **Relay Control Circuitry**

1. Add driver circuits (including transistor drivers, snubbers, and isolation elements as required) for three mechanically bistable relays rated at 230 V/16 A.

2. Connect the relay driver outputs to specific digital output pins of the STM32.

6. **Digital I/O Inputs and Temperature Sensing**

1. Add three digital input circuits with proper signal conditioning for the I/O inputs.

2. Add the DS18B20 temperature sensor circuit along with its required pull-up resistor and connect it to a digital input pin on the STM32.

7. **Safety, Layout, and Mechanical Constraints**

1. Demarcate high voltage (230 V) and low voltage (MCU and sensor) sections in the schematic for clarity and safety.

2. Annotate components and nets to reflect safety clearances and compact layout considerations.

8. **Final Review and Documentation**

1. Review the schematic to ensure all functional blocks are complete and properly interconnected.

2. Document the design decisions and verify that the power distribution, RS485 bus, relay drivers, digital inputs, and sensor circuits meet their specifications.

#Success criteria

- The schematic includes a clearly defined power conversion from 24 V with proper regulation for the STM32 and peripherals.

- A functional RS485 interface linked to the STM32 is present.

- Relay control circuits for three 230 V/16 A bistable relays are properly designed and connected.

- Digital I/O inputs and a DS18B20 temperature sensor circuit are integrated and connected to the MCU.

- The design clearly demarcates high voltage and low voltage circuitry, ensuring safety and manufacturability.

Set Operating Voltage to "24V"

Set Connectivity to "RS485"

Set Domain to "Industrial control"

Set Compliance to "230V mains isolation boundary: 6mm creepage/clearance"

Set Power Requirements to "24V input over Cat5 -> 3.3V logic rail"