This is a custom (manually soldered) ATmega8 board setup with nonblocking code to test common sensors DS18B20 and DHT11/22 with a 128x64 pixel SSD1306 OLED display. The latter provides 8 lines of text, each with 21 symbols.
This code might save someone time in finding the correct libs and fitting everything into 5-6KB. Notice that many sensor libs use direct datasheet demo codes which may block the rest of the code execution or even get stuck in an infinite loop. Beware of any sensor code with "while(something)" that does not bail out after a fixed number of retries.
| Front Side |
|---|
|
| Back Side |
|---|
|
Fuse bits are set in Makefile such that the clock is internal 1MHz (default), USBasp ISP programmer is employed.
The electric circuit diagram is not provided here, but it is similar to this excellent work:
https://github.com/protaskin/AVRThermostat
The sensor and monitor wiring is the following:
- SSD1306: SCL - PC5, SDA - PC4 (no freedom (!), this uses an internal I2C circuitry in ATmega8).
- DS18B20: PD3.
- DHT22: PD2, modify however you like in DHT.h.
- Output: PB0 (see "#define OutX B,0" in main.c).
If you want to change the DS18B20 port letter, just search and replace PORTD, DDRD, PIND in ds18b20nonblocking.c. The pin number is set in main.c:
//DS18b20 is pinned on PD3:
tempS = read_temperature_ds18b20(3);
This is useful if multiple DS18B20 sensors are to be added later without the need of their complex ROM address scanning. Pinning several sensors on different port letters is not recommended, but this can be done with C++ and metaprogramming at the cost of a huge jump in debugging complexity.
If multiple sensors need to be wired on the same pin, it might be better to use the ESP instead of ATmega, see e.g. this MicroPython tutorial. Beware that the ESP12 is terrible at networking or more complex apps due to insufficient RAM, but it could be quite optimal for exactly this specific problem or some mild hobby ADC as it will be much quicker and easier to use MicroPython with built-in tested libs instead of searching for bare C codes on github.
Regarding proper licenses, beware that SSD1306 and I2C have none of them. It is amazing that these libs do the job and fit into 5KB, but I do not generally recommend using a display with such tiny devices other than for occasional testing of sensors. Displaying negative floats or changing fonts might get tricky.
The DS18B20 part is based on a modified old code whose source I can no longer find on github, but see AVRThermostat-MIT for the MIT licensed DS18B20 code which also seems to be non-blocking. The DHT code that I use is DHT22-GPL3, but there is a fairly similar code DHT22-MIT which is also supporting both, DHT11 and DHT22 sensors and is also non-blocking. Notably, when using DHT22-GPL3 with the DHT22 sensor one has to divide the final temperature and humidity values by ten in order to get the correct integer values, while the case of DHT11 does the division internally.
main.c uses a few common pin management macros whose source I can no longer trace back.
In addition to licenses, for massive commercial production one might even need to consider authenticity at the hardware levels, see e.g. counterfeit_DS18B20.
Instead of a display consider sending messages between PC and ATmega8 based on USB and the in-software UART as in
https://github.com/toma3757/ATtiny25-DS18B20-UART
This might allow avoiding any display monitors, their drivers and communication libraries.
Negative temperature values seem to be supported in the codes provided here, but I have not tested this scenario, see DHT22-negative-temperatures with the links to how this is done with Arduino.