This is the first board of the TellMee IoT project, specially designed for IoT projects. It has a host controller, inputs, outputs, external memory, WiFi and LoRa modules. It can be powered by a single lithium-ion battery or connected to the mains.
For the SW development I am using the STM32CubeIDE with C language + FreeRTOS. Internal 5 pins connector available to connect the STLink flash/debug interface.
The host controller interfaces via AT commands to the WiFi and LoRa modules.
Block Diagram
Main Functions
- Two possible power supplies (assembly option), both reverse polarity protected:
Line Supply: input voltage range from 6V to 32V, with a Buck converter to 3.3V;
Battery Supply: input voltage range from 1.8V to 5.5V, with a Buck-Boost converter to 3.3V; - STM32 Arm Cortex M4 32bits, L4 family, low power uC, with 128kB Flash and 64kB SRAM (LQFP48, different uC variants are available in the family);
- Three Digital Inputs, configurable for High or Low active (assembly option);
- Two Analog Inputs, configurable for measuring positive voltage or resistance for temperature sensor (assembly option);
- Two Analog Inputs, configurable for measuring positive voltage or 4-20mA sensor signal (assembly option);
- Two Digital Outputs in open drain configuration, suitable for inductive loads, with max. current of 150mA @24V or 300mA @12V (assembly option);
- One channel serial line RS485, half duplex;
- WiFi communication, according to the standard 802.11 b/g/n, performed by the ESP8266-12F module. Internal PCB antenna;
- LoRaWAN communication, Class A, B and C according to LoRaWAN specification 1.0.3, performed by the RAK3172 module. Supported bands: IN865, EU868, AU915, US915, KR920, RU864, and AS923 (configured via SW). Ipex 1 antenna connector for external antenna;
- Onboard precision Temperature (+/- 0.2°C) and Humidity (+/- 2% RH) sensor, performed by the SHTC3 sensor;
- 8kbit serial EEPROM for system configuration;
- 8Mbit serial flash memory for data logging and firmware update process;
- Buzzer for acoustic warnings, typ. 2.7kHz frequency;
- Three LEDs for visual interface and warnings.
PCB
FR4 two layers, single side SMD assembly, 90 x 60 mm
Assembled Samples
WiFi option only and WiFi + LoRa, working as a gateway for a private LoRaP2P network
The following block was not tested yet:
- SPI Flash Memory
14/Jul/2024