Project Name: Universal IoT Controller (OpenCPU ML307R)
Version: 2.0 (Multi-purpose: Car Wash / Access Control)
Core Module: OneMO (China Mobile) ML307R
1. Project Overview
Design a compact PCB for telemetry and control based on the ML307R LTE Cat.1 module.
Architecture: OpenCPU (No external MCU). All logic is implemented within the ML307R processor.
Application: The board will be used in two modes:
Car Wash/Vending: Counting pulses from Coin/Bill acceptors.
Access Control: Reading RFID cards via Wiegand interface.
2. Power Supply System (Critical Requirement)
The device operates in harsh environments with voltage drops.
Input Voltage: 9V ... 30V DC (Nominal 12V/24V).
Main Regulator: Synchronous Buck Converter (DC-DC).
Target Chip: MP1584EN or TPS54331. DO NOT use LDOs.
Output: Strictly 3.8V (VBAT).
Current Capability: Min 2.5A peak.
Stability: Required Tantalum Capacitor (min 470uF, Case D/E) or Polymer Low-ESR cap (1000uF) on the VBAT line to prevent reboots during LTE transmission.
Protection: Reverse polarity protection (Schottky Diode), PTC Fuse, TVS diode on input.
3. Inputs & Interfaces
A. Payment Inputs (Pulse/Switch)
Qty: 2 Independent Channels (Input 1, Input 2).
Type: Optoisolated (PC817 / EL357).
Connector: Screw Terminal.
Logic: Detect 12V/24V pulses from Coin/Bill acceptors.
B. Access Control Input (Wiegand Protocol)
Qty: 1 Interface (Data 0, Data 1).
Connector: 4-pin Terminal (12V Out, GND, D0, D1).
Level Shifting (CRITICAL):
Wiegand readers output 5V logic.
ML307R GPIOs accept 1.8V max.
Requirement: Implement a Hardware Level Shifter (MOSFET-based or logic IC) to safely connect 5V D0/D1 lines to 1.8V modem GPIOs.
Power Output: 12V passthrough to power the reader (protected by fuse).
C. Communication
UART: 2 ports (JST XH 4-pin) for external Display/Printer.
Must include Level Shifters (1.8V <-> 3.3V/5V).
USB: Type-C (for Firmware Download/Debug).
SIM: Nano-SIM slot with ESD protection.
4. Outputs (Relay Control)
Qty: 2 Channels.
Type: Dry Contact (COM/NO).
Driver: MOSFET (2N7002) driving a small Relay or PhotoMOS (Solid State).
Load: Capable of switching 12V/24V solenoids (with Flyback diode protection).
5. PCB Layout & Form Factor
Reference: See attached photos of the original green board.
Connectors:
Power & Inputs (Pulse/Wiegand) on the bottom edge (Screw Terminals).
Relay Outputs on the bottom edge (Screw Terminals).
UARTs on the side (JST).
Indication (LEDs): Power (3.8V), Net Status, Relay 1 Active, Relay 2 Active.
Mounting: 4 mounting holes (M3).
6. Deliverables
Schematic Diagram (PDF + Source).
PCB Layout (Gerber Files + Source).
BOM (Bill of Materials) with LCSC part numbers.
Pick & Place file (CPL) for assembly.
