make samples/sensor/ds18b20 work with ESP32

[n1ghtrunner]

Problem:

• Try to read d18b20 with the wiring according to sample description.
• The wiring works for nrf52840 soc. Tested with nrf52840dk (via provided overlay) and with nrf52840_mdk_usb_dongle (with a custom overlay file)
• I cannot make it work for the ESP32 NodeMCU board.
• Problems seems to be that either the ESP32 isn't able to handle it from the electrical perspective or I didn't define the overlay right.
• Of course tried different overlay configurations, partially modifying the properties of uart2/group1 and uart2/group2, but no success in any combination.

Scenario Description:

• Sample: sensors/ds18b20
• Board: AI-Thinker ESP32 NodeMCU Dev Board.
  • Pinout looks like this one
• ds18b20 wiring:
  • one single sensor
  • 1-wire bus line wired to uart2 (on gpio pins 16/17 - both directly connected).
  • ds18b20 V+ connected to 3.3v V+ of NodeMCU board. GND accordingly.
  • 4.7kΩ between 1-wire bus line and V+
  • Also tried variations with schottky diode (with optional 220Ω/480Ω) between 1-wire bus line and TX (on ESP)
• Using board configuration: esp32
• Using custom overlay file: <sample directory>/boards/esp32.overlay

Content of esp32.overlay:

&uart2 {
	status = "okay";

	w1: w1 {
		compatible = "zephyr,w1-serial";
		status = "okay";

		ds18b20 {
			compatible = "maxim,ds18b20";
			family-code = <0x28>;
			resolution = <12>;
			status = "okay";
		};
	};
};

&uart2_default { 
  group1 {
    bias-pull-up;
    drive-open-drain;
  };
};

Alternative solution without zephyr

• There is a 3 year old code to make the same setup work with esp-idf: esp-idf-onewire. I tried to compile this with recent and some older versions of esp-idf to validate the electric setup. However no success - always fails with some linking error at the end of make execution.
• The author suggests to have 1-wire on 5v (with signal level converter between ESP32 and 1-wire) and not 3.3v. However, since the 3.3.v setup works flawlessly on the nordic boards this does not seem to be the issue.

[rftafas]

Hi!

FWIW, alternative ESP-IDF solution would be this one: https://github.com/espressif/esp-idf/tree/master/examples/peripherals/rmt/onewire_ds18b20

[n1ghtrunner]

Of course any of the examples that use bit-banging on an arbitrary GPIO port work easily (esp-idf, Arduino, ...). Nevertheless Zephyr supports only 1-Wire on UART. I do not want to solve the problem - I want to solve it with zephyr to achieve a solution where I can reuse my partial solution for different boards (nrf52840, esp32, ...).

[rftafas]

If the bit banging example works, at least for a slow signal you will know it is electrically right. Then you can go back to Zephyr and test over the same setup. I would suggest starting with same speed used on bit banging.

If even the bit-banging is not doing it, there might be other issues.

Also, you may already have your Zephyr updated, but always worth suggesting using the latest version.