Embedded Hardware & PCB Developer

Embedded Hardware & PCB Developer Required (ESP32, Quectel + 4G Voice Calling Device) We are looking for an experienced Embedded Hardware and PCB Design Engineer to develop a custom electronic device for a social impact project. The purpose of this project is confidential, so applicants should be comfortable working under a Non-Disclosure Agreement (NDA). Project Requirements Design and develop a compact PCB with the following features: * ESP32 microcontroller * 4G LTE GSM module (preferably Quectel or equivalent) * Nano SIM card slot * USB Type-C charging * Built-in rechargeable Li-ion/Li-Po battery charging and protection circuit * Single push button integrated on the PCB * 3.5 mm audio jack for connecting a telephone-style handset * Microphone and speaker audio support through the audio jack * Battery level monitoring * Low power consumption and efficient power management * Compact PCB layout suitable for enclosure mounting Functional Requirements * When the push button is pressed and held for approximately 5 seconds, the device should automatically initiate a voice call to a predefined phone number. * Once the call is connected, the user should be able to communicate using the connected handset. * The phone number should be configurable through firmware. * The system should be reliable, stable, and suitable for continuous field deployment. Deliverables * Complete schematic design * PCB layout and routing * Bill of Materials (BOM) * Gerber files * Firmware source code * Prototype bring-up support * Manufacturing support for PCB assembly if required * Documentation explaining the hardware and firmware Required Skills * Embedded Systems * ESP32 Firmware Development * PCB Design (KiCad, Altium, or EasyEDA) * GSM/4G LTE Modules (Quectel preferred) * USB Type-C Power Design * Audio Circuit Design * Battery Charging & Power Management * Hardware Testing & Debugging Preferred Experience Applicants who have previously developed GSM calling devices, IoT hardware, emergency communication devices, industrial electronics, or custom embedded products will be given preference. Please include: * Examples of similar projects you have completed. * Which GSM module you recommend and why. * Estimated timeline. * Estimated development cost. * Whether you can assist with prototype manufacturing and testing. Confidentiality is very important for this project. Selected freelancers will be required to sign an NDA before detailed project information is shared.