ESP-Nodes

Eco-system of ESP32s Nodes and ATtiny85 peripherals with different functionalities.

The ESP32-Node is designed to be a low-cost, vanila solution for experimenting with embedded and IoT devices. The ESP32-Node is intended to College students taking Electronics program or advanced users who are looking for functional ESP32 embedded board with minimal size.

ESP32-Node Features:

• Uses bare-bones ESP32-WROOM-32D Module ¹
• Direct connections to all GPIOs
• Miniature in size; only 35.7mm x 35.7mm
• Built-in 3V3 voltage regulator (V_max=15V) and reversed supply voltage polarity protection
• Pre-wired strapping pins for ensuring proper booting on power-on
• blue power-on LED
• two programmable LEDs
• programmable via UART -> no need for serial drivers

ESP32-WROOM-32D Module Adapter Pinouts

The adapter allows interchangability of ESP32 modules between different nodes. The adapter contains minimal components on its PCB, just enough to ensure module's operation. (ESP32 8-N-1)

Physical Pin	Descrption and Logical Pin	Extended Function
1 15 38	Ground
2	3V3
3	EN
4 5 6 7	Inputs Only GPIO36 GPIO39 GPIO34 GPIO35	ADC1_CH0, ADC1_CH3, ADC1_CH6, ADC1_CH7
8 9	GPIO32 GPIO33	TOUCH_9, TOUCH_8
10 11	GPIO25 GPIO26	DAC_1, DAC_2
12	GPIO27	TOUCH_7
13 14	GPIO14 GPIO12	HSPI_CLK HSPI_MISO TOUCH_6 TOUCH_7
16	GPIO13	HSPI_MOSI ADC2_CH4
17 18 19 20 21 22	Module Internal Use Only GPIO09 GPIO10 GPIO11 GPIO08 GPIO07 GPIO06
23 24	GPIO02 GPIO15	AD2_CH3 ADC2_CH2
25 26	GPIO00 GPIO04	TOUCH_1 TOUCH_0
27 28	GPIO16 GPIO17	UART2_RXD UART2_TXD
29 30 31	GPIO05 GPIO18 GPIO19	VSPI_CS0 VSPI_CLK VSPI_MISO
32	Not Connected
33	GPIO21	SDA
34 35	GPIO03 GPIO01	UART0_RXD UART0_TXD
36	GPIO22	SCL
37	GPIO23	VSPI_MOSI

Programming via UART

Bare-bones ESP32 module can be programmed via UART interface (GPIO03 and GPIO01) using USB to UART adapter.

Temperature Node. The Key Elements and Components

The Temperature Node broadcasts the air temperature, atmospheric pressure and air humidity over secured MQTT.

I2C Air Temperature, Pressure and Humidity Sensor Board (BME280)

BME280 is combined temperature, humidity and pressure sensor. The unit combines high linearity and high accuracy sensors and is perfectly feasible for low current consumption, long-term stability and high EMC robustness. The humidity sensor offers an extremely fast response time and therefore supports performance requirements for emerging applications such as context awareness, and high accuracy over a wide temperature range.²

Below is the functional diagram of BME-/BMP-280. Notable difference between the two devices, is that BME-280 is capable of measuring relative humidity. BME-280 has square shape, while BMP-280 has rectangular shape.

BME-280 can come in a ready-to-use PCB ...

Important

BME280² and BMP280³ look almost identical. However, BME280 sensor has a square form, while BMP280 has a rectangular form. In addition, the two sensor boards can have different I²C addresses.

4-pin variant

The BME280 sensor board interface uses 4 pins and is 13mm by 10.5mm in size. The four pins are VIN, GND, SCL and SDA. The measured values are sent via I²C protocol. The I²C slave address is pre-defined and can take value either 0x76 or 0x77 (BME280 Datasheet, page 32)⁴.

Wiring

Pin	ESP32 GPIO
SCL	GPIO22
SDA	GPIO21

Reading Values

i2c_master_write_read_device(I2C_MASTER_NUM, 0x76, &reg_addr, 1, data, len, I2C_MASTER_TIMEOUT_MS / portTICK_PERIOD_MS);

Data readout is done by starting a burst read from 0xF7 to 0xFC (temperature and pressure) or from 0xF7 to 0xFE (temperature, pressure, and humidity). The data are rad out in an unsigned 20-bit format both for pressure and for temperature, and in an unsigned 26-bit format for humidity. After the uncompensated values for pressure, temperature, and humidity have been read, the actual humidity, pressure and temperature needs to be calculated using the compensation parameters stored in the device.

BME-/BMP-280 can communicate via I²C. The two diagrams below summarize algorithm of reading and writting values to/from the sensor.

---

REFERENCES

---

1. https://www.espressif.com/sites/default/files/documentation/esp32_datasheet_en.pdf ↩︎

2. https://www.bosch-sensortec.com/products/environmental-sensors/humidity-sensors-bme280/ ↩︎

3. https://www.bosch-sensortec.com/products/environmental-sensors/pressure-sensors/bmp280/ ↩︎

4. https://www.bosch-sensortec.com/media/boschsensortec/downloads/datasheets/bst-bme280-ds002.pdf ↩︎