PCB Design for 125 kHz Transponder Reader

Project Title Schematic & PCB Design for ATmega32U4 + PCF7991 125 kHz Transponder Reader with USB Interface Project Overview I am looking for a skilled electronics engineer or PCB designer to create a schematic and PCB layout for a device that uses: ATmega32U4 (5 V, native USB support, 44TQFP package) PCF7991 RFID base station IC (operating at 5 V, 125 kHz) USB interface for communication with a PC (no external USB–serial chip required) This device will transmit and receive data at 125 kHz for transponders (e.g., automotive immobilizer tags) using the PCF7991 and a coil antenna. The ATmega32U4 will handle the low-level bit-banging, timing, and decoding, while appearing as a USB CDC device (virtual COM port) on the PC side. I have existing Arduino-based code (.ino) that demonstrates how to interface with the PCF7991 (originally for an ATmega328). We plan to port or adapt that code for the ATmega32U4 once the PCB is complete. Objectives Develop a Complete Schematic that includes: ATmega32U4 microcontroller with supporting components (crystal/oscillator if needed, decoupling capacitors, etc.). PCF7991 base station IC, operating at 5 V. All required external components for the PCF7991 (matching network, antenna connections, etc.) according to the datasheet. USB connector (micro-USB or USB‑C), along with ESD protection, D+/D− resistors, and any recommended USB hardware design practices. Power supply circuitry (5 V regulator from USB or external DC input). ISP header (MOSI, MISO, SCK, RESET, VCC, GND) for initial programming/bootloader flashing. Spare GPIOs routed to a header for potential future expansion. Design the PCB Layout: 125 kHz antenna printed on the PCB itself. Strategic component placement and routing for RF performance (125 kHz antenna area). Correct routing of the 4 MHz clock signal from the chosen clock module to the PCF7991 (since we plan to feed a fixed clock module). Robust grounding practices, minimal noise coupling into the RFID front end. Standard mounting holes or mechanical outlines (if required). Deliver Manufacturing-Ready Files: Schematic in the chosen EDA tool (Eagle, KiCad, Altium, etc.) + PDF export. PCB layout files + Gerber files for manufacturing. Bill of Materials (BOM) with part references and key component numbers. Key Requirements & Notes 5 V Operation Both the ATmega32U4 and PCF7991 run at 5 V. No level shifting is necessary for the main signals. USB Connectivity The ATmega32U4 must enumerate as a native USB device—no external USB–serial chip. Include appropriate ESD protection and data-line resistors per Atmel/Microchip guidelines. 125 kHz Antenna & PCF7991 The PCF7991 requires an external coil and matching network. Follow the datasheet for correct tuning and signal integrity. Provide test points or a method to measure the coil’s resonant frequency if possible. Clock Generation The PCF7991 needs a ~4 MHz clock input. We plan to supply this clock from a dedicated 4 MHz oscillator/module (simplifies firmware). Programming / Bootloader We intend to use a Caterina (Leonardo-style) bootloader or a custom USB bootloader. Please add a 6-pin ISP header for initial programming/fuse setting. Form Factor & Size Constraints If you have any recommended board size or shape, please propose. Include at least four mounting holes or mechanical fixings if space permits. Deliverables Schematic Complete in the agreed EDA tool. A readable PDF version. PCB Layout Source files in the chosen EDA tool. Clear labeling of components, reference designators, and any test points. Manufacturing Files Gerber files (RS-274X or extended Gerber). Drill files, pick-and-place files (if assembly needed). Bill of Materials (BOM) Component references, quantity, package, and part numbers. Recommendations for footprints compatible with major distributors (Digi-Key, Mouser, etc.). Budget I am open to fair market bids. Please specify: Your fixed price. The expected total cost range based on the scope. Qualifications Experience with ATmega32U4 or other AVR MCUs with native USB preferred. Familiarity with RFID / 125 kHz front-end design (PCF7991 or similar) is a plus. Ability to deliver production-ready Gerber files and BOM. Please share any relevant examples of prior designs (USB-enabled MCUs, transponder/RFID interfaces, etc.). How to Bid In your proposal, please indicate: Relevant Experience: Summarize any comparable projects and tools you plan to use. Design Tool: Specify which EDA tool (Eagle, KiCad, Altium, etc.) you’ll use. Estimated Cost & Timeline: Provide an estimate for each phase and the total project duration. Deliverables: Confirm you can provide schematic, PCB layout files, Gerbers, and BOM. Thank You! I look forward to reviewing your bid and working together to bring this ATmega32U4 + PCF7991 project to life. If you have any questions or suggestions, please let me know!