This example demonstrates how to utilize UART interfaces of ESP32 to use as OneWire bus.
It uses a few DS18B20 sensors to scan a bus and write SEARCH/CALC command.
The advantage of the library is its tremendous speed and full hardware implementation.
This implementation allows the execution of other threads in parallel with the main thread while maintaining operability.
The accuracy of operations is determined by the UART subsystem.
The example can be run on any ESP32 development board connected to a PC with a single USB cable for flashing and monitoring. The external interface should have 3.3V outputs. You may use e.g. 3.3V compatible USB-to-Serial dongle if your board doesn't containt it.
The DS18BB20 sensor works from 5V. In this case you MUST use 3V3 to/from 5V logic level converter. For an example like that:
^ 3v3 ^ 5v
| |
| |
*---------- |
/ | G /
4.7K \ |_______ \ 4.7K
/ _ _ _ /
| | ^ | |
TX ----|<---*----------|--|--|--------*------ 1-wire bus
Schottky | S | | D
Diode | --->|--
RX ---------| N-Channel
Mosfet (BSS138 like)
Please take note that Schottky diode is necessary!
In a few cases you can try to use DS18B20 on 3.3v power supply without any mosfet. Anyway you MUST use Schottky diode.
Connect the external serial interface to the ESP32 board as follows.
| ESP32 Interface | #define | ESP32 Pin |
|---|---|---|
| Transmit Data (TxD) | OW_UART_TXD | GPIO16 |
| Receive Data (RxD) | OW_UART_RXD | GPIO17 |
| Ground | GND | GND |
| 3v3 | VCC | VCC |
| DS18B20 | ESP32 Pin |
|---|---|
| 1-wire bus | Signal Line |
| 5V | VDD -- External 5V supply |
| Ground | GND |
Optionally, you can set-up and use a VDD that has +3.3V
idf.py menuconfig
- Set serial port under Serial Flasher Options.
Build the project and flash it to the board, then run monitor tool to view serial output:
idf.py -p PORT flash monitor
(To exit the serial monitor, type Ctrl-].)
There are three sensors on the 1-wire bus:
I (10) 1wire: Scan OW bus...
I (80) 1wire: DS18B20[0x28] sens id: 0x80000003D568 (CRC F4) -- 25.937500 (C)
I (100) 1wire: DS18B20[0x28] sens id: 0x80000003E20A (CRC 8C) -- 26.250000 (C)
I (130) 1wire: DS18B20[0x28] sens id: 0x041663B9BCFF (CRC 42) -- 45.875000 (C)
I (130) 1wire: Presence correct. SCAN found 3 devices on the bus
I (3130) 1wire: PRESENCE detected on 1-wire bus. Presence signal: 1
I (3130) 1wire: Scan OW bus...
I (3200) 1wire: DS18B20[0x28] sens id: 0x80000003D568 (CRC F4) -- 25.937500 (C)
I (3220) 1wire: DS18B20[0x28] sens id: 0x80000003E20A (CRC 8C) -- 26.250000 (C)
I (3240) 1wire: DS18B20[0x28] sens id: 0x041663B9BCFF (CRC 42) -- 45.875000 (C)
I (3240) 1wire: Presence correct. SCAN found 3 devices on the bus
I (6240) 1wire: PRESENCE detected on 1-wire bus. Presence signal: 1
I (6240) 1wire: Scan OW bus...
I (6310) 1wire: DS18B20[0x28] sens id: 0x80000003D568 (CRC F4) -- 25.937500 (C)
I (6330) 1wire: DS18B20[0x28] sens id: 0x80000003E20A (CRC 8C) -- 26.250000 (C)
I (6350) 1wire: DS18B20[0x28] sens id: 0x041663B9BCFF (CRC 42) -- 45.875000 (C)
I (6350) 1wire: Presence correct. SCAN found 3 devices on the bus
I (9350) 1wire: PRESENCE detected on 1-wire bus. Presence signal: 1
I (9350) 1wire: Scan OW bus...
I (9420) 1wire: DS18B20[0x28] sens id: 0x80000003D568 (CRC F4) -- 25.937500 (C)
I (9440) 1wire: DS18B20[0x28] sens id: 0x80000003E20A (CRC 8C) -- 26.250000 (C)
I (9460) 1wire: DS18B20[0x28] sens id: 0x041663B9BCFF (CRC 42) -- 45.875000 (C)
I (9460) 1wire: Presence correct. SCAN found 3 devices on the bus
Logic Analizer:
Thanks to @andrei15, who was actively involved in the development of this project.
#todo Separate library and example codes into individuals projects.
I had to spend almost a month to figure out the HAL / SOC esp-idf. There is no advertising in the project, everything is clear and on the case, ready for commercial operation completely free.
I'm looking for an interesting jobs in field of uC. If you have one write on [email protected]