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 (Vmax=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](https://github.com/alexandrebobkov/ESP-Nodes/tree/main?tab=readme-ov-file#uart) -> no need for serial drivers ### ESP32-WROOM-32D Module Adapter PinoutsThe 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 |
[^1]: https://www.espressif.com/sites/default/files/documentation/esp32_datasheet_en.pdf
### 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 Thermostat (LM75A)
The LM75A is an industry-standard digital temperature sensor. The LM75A provides 9-bit digital temperature readings with an accuracy of ±2°C from –25°C to 100°C
and ±3°C over –55°C to 125°C. The LM75A operates with a single supply from +2.7 V to +5.5 V. Communication is accomplished over a 2-wire interface which operates up to 400kHz.
The LM75A has three address pins, allowing up to eight LM75A devices to operate on the same 2-wire bus. The LM75A has a dedicated over-temperature output (O.S.) with
programmable limit and hysteresis. This output has programmable fault tolerance, which allows the user to
define the number of consecutive error conditions that must occur before O.S. is activated.
```text
address: 0x49
```
### 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]
> BM**E**280[^2] and BM**P**280[^3] 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
```C
i2c_master_write_read_device(I2C_MASTER_NUM, 0x76, ®_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.
## Display Node
```text
OLED address = 0x3C
0.91" 128x32
```
---
## REFERENCES
[^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