Off The Grid Messenger
Off The Grid (OTG) Messenger is an easy way for people to communicate through text messages when in remote areas. With a theoretical transmission range of 10 miles (16kms), OTG messenger can be used by groups of people to stay connected when they are in areas not serviced by mobile connectivity.
For portability and low power purposes, the device was created by re-purposing an old Nokia e63 phone I had laying around. The enclosure, LCD, keypad, backlighting and speaker have been re-used however the motherboard was re-designed from the ground up with low power components, a modern STM32 H7 microcontroller, an ISM LoRA radio and expanded flash memory.
Here's the device boot screen
Common use cases
Why was this device created? It was developed as a science project to learn/teach everything about the STM32 ecosystem of products, hardware engineering, embedded systems engineering, and encrypted communications.
This is considered an 'advanced' project so if you're just starting out with embedded systems or have only ever used the arduino platform then the concepts shown here could be challenging. You should be familiar with C/C++, SWD debugging, ARM core knowledge along with bare metal device driver development.
Main Menu after boot
User interface developed with the amazing TouchGFX GUI builder created by ST. The e63 doesn't support touch and TouchGFX doesn't work with keypads or buttons so interfacing the keypad to the GUI engine was not a trivial exercise.
Hardware breakdown
Software breakdown
Development Feature Roadmap
Custom 4 layer PCB, designed to fit the Nokia e63 Enclosure
PCB Images. Back of PCB
Board Schematics and Design I'll publish the motherboard if I get some positive interest in this project from the community. Contact me here: [email protected]