USB Thermometer on the microcontroller. Scheme, description

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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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USB thermometer on the microcontroller. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Microcontrollers

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The ATmega8 was chosen as the microcontroller. Digital temperature sensor: DS18B20, which has temperature measurement limits from -55 to +125 degrees Celsius. In general, here is a list of everything you need for a thermometer:

ATmega8 microcontroller (preferably without the "L" index at the end).
Temperature sensors DS18B20, required without PAR index at the end, otherwise max. temperature will be +85 degrees.
Quartz 12 MHz.
2 capacitors 22 pF and one capacitor for power supply (10V and at least 100 Mf, because USB has terrible voltage drops on the power line).
2 resistors 68 Ohm, 1 resistor 200 Ohm, 1 resistor about 2,2 - 4,7 kOhm, 1 resistor 10kOhm and 1 resistor 1,5kOhm.
2 zener diodes 3.6V.
USB plug or socket.
Light-emitting diode.
Well, a signet or a mock-up on which it will all be assembled.

Device Diagram:

(click to enlarge)

The scheme is very simple. On the left are all 4 USB pins. Capacitor C3 is the same power supply. Zener diodes VD1 and VD2 reduce the voltage on the data line to 3,3V. Sensor DS18B20 You can not put it on the board, but bring it to the right place, in general, the wire length can be up to 100 meters, but I do not recommend more than 50m. The LED changes its state (lights up / goes out) each time the temperature measurement is started. If it blinks at a chaotic speed, then the temperature sensor is working normally, if it is constantly lit or not lit - there is a problem with the sensor (incorrectly connected, non-working, or a very long wire, near which there is strong electromagnetic interference). On the right is a connector for in-circuit programming of the microcontroller.

Firmware for it - USBThermometer\MCU\USB_thermometer\default\main.hex. After uploading the firmware, you need to set the fuses correctly, otherwise the device will not work, in STK500 from AVR Studio it looks like this:

USB thermometer on the microcontroller. fuses

If you correctly assembled the device and correctly flashed the MK, then when you connect to your computer via USB, Windows will find a new device and ask where the driver is. It is located in the folder USBThermometer\windows-driver\, where you need to specify the path. When the driver installs, restart your PC. Then run the program USBThermometer.exe.

If the device is not connected, then "Not connected" will be written instead of the temperature. and when dragging, the window will "freeze" a little every second, because the program will update the data on connected devices every second until it finds this thermometer. If you connect the device, then the message "Thermometer is connected" will pop up in the tray, the window will no longer freeze, and you will see this:

USB thermometer on microcontroller

Also, which is very convenient, there is a function "Mini-window" and "On top of all windows". I usually check all 2 checkboxes and get this:

USB thermometer on microcontroller

The whole gray area is the program window in "mini-view" (the white-blue background with bulbs is the desktop). Like :) ? This is convenient because the window is small (96x198), always on top of all windows and does not interfere with other applications. In addition, the program is not displayed on the taskbar, but only in the tray, and by hovering over the program icon, you can see the temperature in Celsius:

USB thermometer on the microcontroller. Trey

I tested this thermometer on several stationary PCs, laptops and netbooks under Windows Home Edition, Windows Professional and Windows Vista operating systems. Everything worked great! Only here on whist, at a temperature on the temperature sensor below -9 and above 99 degrees. the letter "C" (where the temperature is in Celsius) was not visible, because I chose the font for displaying the temperature "Comic Sans MS", but I do not think that this is a problem for anyone.

Program, firmware, sources and driver: Download (500 kb)

PS If you do not have a programmer and you need an already flashed microcontroller or you want to buy a ready-made thermometer, then contact me by e-mail: devices2000 {stsobaka} ya.ru

I also accept orders for the development and manufacture of devices on microcontrollers, for this please contact the same email.

Author: Mikhail Brazhnikov, devices2000 {stsobaka} ya.ru; Publication: cxem.net

See other articles Section Microcontrollers.

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