Digital thermometer on LM75AD sensor. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Microcontrollers
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This device is designed to measure air temperature in the range from zero to +45 degrees.
Fig. 1
The thermometer is controlled by an ATtiny2313 microcontroller configured to operate at a clock frequency of 1 MHz from an internal oscillator.
To measure the temperature, a digital sensor LM75AD with an I2C interface was used. According to the I2C line specification, the LM75AD chip has a seven-bit address. The upper four bits of the address are set rigidly: 1001, the lower three are set on the pins A0, A1, A2, by applying logical 0 or 1 to them.
The LM75AD includes a pointer register whose code selects the desired data register and four data registers. Code 0x00 selects a two-byte read-only temperature register that stores the current temperature code. In table. 1 shows the placement of data in this register. If the D10 bit in the temperature register is 0, then the temperature is greater than 0 and is calculated using the formula T=(Temp_data) x 0.125.
Fig. 2
To display the temperature, a TIC5234 liquid crystal indicator is used. When data is transmitted to the indicator, the most significant bit, which controls segment 49, is transmitted first. Then the bit of segment 48 is transmitted, and so on, until all bits have been transmitted. After that, you need to latch the register by setting LOAD to the log. 0. In this case, the selected segment configuration will be displayed on the indicator. Log. 1 corresponds to the included segment, Log. 0 - off state.
The device is powered by a 9-volt "Krona" battery. To reduce the voltage, an L78L33 stabilizer was used with an output voltage of 3.3 Volts and a maximum current of 100 mA.
The drawing of the board is shown in fig. 3. Also on the board is a connector for in-circuit programming.
Fig. 3
On fig. 4 photo of the board with installed components.
Fig. 4
Fig. 5
Download HEX firmware, SPL file and PCB in LAY format
Author: Pavel Baranov (KVorb), sirkvorb [dog] gmail.com, icq: 541293; Publication: kvorb.ru
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