Simple and inexpensive thermometer for PC, which allows you to measure and record the temperature of 8 and temperature sensors. An apparatus adapted for data transmission over the Internet. Communication with the computer via an RS232 serial connector. As temperature sensors used DS1820 which communicate with the system via a single-wire bus. The result can be represented by a thermometer equipped with a large number of sensors, and the temperature can be measured at many points simultaneously.
- temperature sensors: DS1820
- maximum number of sensors: 8
- Connection to the computer: RS232 connector
- the ability to work on the Internet
- software for Windows XP
- nutrition: from your computer (RS232 connector)
Schematic diagram is shown in Figure. 1.
Communication with the computer by RS-232 serial link. Scheme fed by DTR. Since the RS-232 port is operating at voltages in the range of even -25 AT … + 25 AT, it was necessary to use a zener diode D1, to reduce it to a voltage 5 AT, required for systems DS1820. Work-Wire bus is as follows:. Setting status 1 (a negative voltage) Output TXD RS-232 port closes the transistor T1 (BC548B). At the moment, with a resistor R1 idling state, i.e + 5 AT, supported on line. The transistor T1 is connected to the emitter of minus. If the circuit while the transistor exceeds 480 microsecond, DS1820 will accept it as the reset signal. Sending a logic zero on the DS1820 chip through a transistor T1. If a computer sends a logic signal, it will establish a positive voltage on output RTS. This will overload the load on the capacitor C1. At the same time diode D2 will prevent the voltage on the data line to exceed 5V. Then RTS line is set to a negative voltage, and a capacitor C1 is charged through the elements R1, R2 and D3. The capacitor is charged approximately 5 microsecond, DS1820 sensors interpret this as a short pulse of logic signal. Now, if you send a single-circuit 0, line data in these systems will be shorted to ground. At this moment, a positive voltage appears at the cathode of diode D3, and the anode – negative. Elements U1 chip type 4011 establish a high input pulse CTS. Such a pulse will be remembered by the system register. As soon as the control program will finish the current function, she will be informed that, that the 1-Wire line submit Puzzle.
Installation and setup
sample assembly was formed on the printed circuit board, shown in Figure. 2.
The maximum number of temperature sensors, which can be connected to each terminal – 8. Now you can connect the assembled system to the PC and run the program. Program to work with the thermometer must be run with a resolution of at least 1024×768. The program automatically detects the connected circuit and begins temperature measurement.
Applications shown in Figure. 3.
We can change the description of each thermometer, selecting it, and after a short press on its default name is used «no_name». After closing the window circuit will still work in the background, and will only be visible icon next to the clock in the panel. If you hover the mouse pointer over the icon, you will get information with all sensor names and measured temperatures. One click on this icon opens the application window. The program closes completely after pressing the button "Finish" in the application window.
The program can save data to a file for further editing, For example, spreadsheet. To do this, type the path to the file in the "File Path", enter the number of seconds to record and check the box "Register file". Still it is possible to adapt the system for the Internet. Due to the nature theme instructions for this procedure are available for download in digital form from the website. The manual contains many illustrations, and installation is very simple, even for beginners. Appearance of the program – thermometer in the browser can be seen in Figure. 4.