ATtiny85 DS18B20 Thermostat

Thermostat with DS18B20 temperature sensor and ATtiny85 microcontroller:

• Watchdog activated, 2s.
• Average calculation between readings.
• Displaying the temperature value does not block the temperature reading.
• In case of communication failure with the sensor, attempts are made to reestablish the communication.
• Configurable hysteresis:
• • Output is activated when the temperature value is above the pre-established value (variable "temp_max_setpoint").
• • Output is deactivated when the temperature value is below the pre-established value (variable "temp_min_setpoint").
• Alternating warning output for when the output is activated (for active Buzzer/Beeper).
• In the event of a communication failure, after 5 attempts to reestablish the communication, the output is automatically activated.
• Output update time is dependent on the number of readings for average readings and the reading precision:
• • For 9-bit precision and 5 average readings, the time is approximately 0.5s.

Temperature value display by flashing LED:

• Zero value on the left is ignored, is not displayed.
• The zero value of the digit has a longer duration than for the digits between 1 and 9, and a shorter time than for the negative value signal
• Digit values between 1 and 9 are displayed with short pulses.
• Negative sign is displayed with long time.
• The duration of each pulse is dependent on the reading time of the sensor, if the reading precision is changed to more bits, the time increases.

Note:

• In version 2, the terminals of the 2 sensors are connected in parallel.
• R5 has been modified from 4.7k to 2.2k to slightly increase the brightness of the green color LED.
• Pay attention to the quality of the 1nF capacitor.

Dependencies:

Library:

https://github.com/milesburton/Arduino-Temperature-Control-Library

Board:

https://github.com/SpenceKonde/ATTinyCore

Notes:

• "After changing the clock source, BOD settings, or whether to save EEPROM on chip erase), you must do "Burn Bootloader" with an ISP programmer" (From: ATTinyCore)

• When the chip is blank or the chip has a pre-installed Bootloader, you must do "Burn Bootloader" as well.

• Due to the fake DS18B20 issue, the test sketch was created to help identify bad sensors: Time_Checker (9bits)

• • There are sensors being sold that do not even come close to the datasheet specifications:

• (Analog.com) Guidelines for Reliable Long Line 1-Wire Networks

• DS18B20 Calibration? See here: DS18B20 1-Wire calibration with Arduino: Finally nailed it!.

Arduino IDE:

https://www.arduino.cc/en/software/

• Note: Compiled with Arduino IDE 1.8.13

Settings:

Arduino IDE - Burn Bootloader:

(Bootloader is not used for this code, but it is necessary to burn the bootloader to reconfigure the fuses)

IDE settings for compilation and upload:

Tested programming method:

• Arduino as ISP: https://www.arduino.cc/en/Tutorial/BuiltInExamples/ArduinoISP

• USBasp - USB programmer for Atmel AVR controllers: https://www.fischl.de/usbasp/

Sketch upload via programmer:

Schematic for ATtiny85 DS18B20 Thermostat (For version 1, only 1 sensor):

avrdude error:

• avrdude: error: could not find USB device with vid=0x16c0 pid=0x5dc vendor=’www.fischl.de’ product=’USBasp’

On some system. A tty device is created when USBasp is connected. In my case /dev/ttyS0. However when Port is set to /dev/ttyS0 in Arduino IDE. You will see the following errors:

avrdude: Warning: cannot open USB device: Permission denied avrdude: error: could not find USB device with vid=0x16c0 pid=0x5dc vendor=’www.fischl.de’ product=’USBasp’

• To Fix Permission denied error. As root edit “/etc/udev/rules.d/99-USBasp.rules” with the following:

$ sudo nano /etc/udev/rules.d/99-USBasp.rules

SUBSYSTEM=="usb", ATTRS{idVendor}=="16c0", ATTRS{idProduct}=="05dc", GROUP="dialout"

• Add self to dialout user group.

sudo usermod -aG dialout $USER

• Then logoff and login again.
• • ---> Unplug USBasp device <--- Then restart udev.

sudo /etc/init.d/udev restart

• Source: Geting USBasp v2.0 to work with Linuxmint

Software License:

This library is free software; you can redistribute it and/or modify it under the terms of the GNU Lesser General Public License as published by the Free Software Foundation; either version 2.1 of the License, or (at your option) any later version.

This library is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public License for more details.

You should have received a copy of the GNU Lesser General Public License along with this library; if not, write to the Free Software Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA

Hardware Licence:

• Released under CERN OHL 1.2: https://ohwr.org/cernohl