I was approached by the Isles of Scilly Community Venture to build the hardware to enable their new community car sharing scheme for local residents and contractors. A goal of the scheme was to reduce the island’s dependency on fossil fuels by having a fleet of electric cars, all charged over solar power with vehicle-to-grid functionality, available to use by local residents, administered and run by a local non-profit. With the help of the European Regional Development Fund they purchased a fleet of Nissan electric vehicles, but needed a software and hardware solution to allow users to hire and unlock cars, as well as to remotely monitor battery status, tyre pressure, mileage, and other vehicle telemetry.
Design
We investigated existing solutions but had some particular constraints which necessitated a ground-up solution:
- Mobile signal is nonexistent on some parts of the island.
- Electric vehicles have a very small auxiliary 12V battery; current draw at idle should be under a few milliamps to not discharge the battery over multiple weeks without use.
- Remote locking and unlocking of Nissan electric vehicles was needed, via an app or NFC card, while keeping the same low idle current draw.
- The cars need to be hired by untrained users, so clear visual feedback and an easy UX flow was necessary.
I opted to design a single-PCB solution to the following specification:
- 100mm diameter circle in a custom enclosure with translucent diffusers around the outside
- 16 individually addressable RGB LEDs around the perimeter for feedback (multicolour swirls to show processing/locked/unlocked status)
- CAN bus transceiver wired to OBD-2 connector for power and communicating with car
- ESP32-S3 microcontroller with WiFi for telemetry at base stations and locking/unlocking
- MFRC522 MiFare/NFC card reader for lock/unlock over WiFi (and force unlock with master card) with custom PCB antenna for 10cm NFC range (through windscreen)
- GPS/Glonass/Beidou multi-band GNSS receiver for position tracking
- Semtech SX1262 LoRaWAN for telemetry when away from base station (with LoRaWAN network deployed around the island)
- SIM7600 quad-band 4G receiver to allow future telemetry / firmware updates over mobile network
- Onewire iButton support to detect car keys returned
All firmware written in C with ESP-IDF HAL, interacting with a custom Django-based web app written by George Goldberg.
Roles
Hardware design and manufacture, mechanical case design, firmware
George Goldberg: software, UI
Year
2021-present
