The application of FC-135R 32.768kHz crystal oscillator in electronic thermometer

Apr 09,2024
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In the new type of intelligent electronic thermometer, the accuracy of clock display is very important. The timing module unit, combined with Epson Danghong 32.768kHz crystal FC-135 or FC-135R, forms a real-time clock module unit, allowing the entire design to display timing information while accurately displaying the measured body temperature.

Electronic thermometers typically require components such as temperature sensors, microcontrollers, and display digital tubes to display temperature measurement results. The popular electronic thermometer is now more intelligent, with added functions such as over temperature alarm and clock display, making it convenient for users to check temperature changes on a regular basis. In the new type of intelligent electronic thermometer, the accuracy of clock display is very important.

The above picture is an intelligent electronic thermometer solution that can achieve precise clock display. The working process of this electronic thermometer:

When the temperature measurement button is pressed, the system converts the electrical signal collected by the temperature sensor into a digital signal through the A/D interface of the microcontroller;

The microcontroller processes the received digital signals and inputs them into the display circuit, ultimately displaying the test results.

The display time information is synchronized through the timing module unit, making it convenient for users to measure and track temperature

The timing module unit is combined with a 32.768KHz crystal to form a real-time clock module unit, allowing the entire design to display timing information while displaying the measured body temperature.

Real time clock modules are generally high-performance, low-power, RAM equipped real-time clock circuits that can accurately time years, months, days, weekdays, minutes, and seconds, and most of them have leap year compensation function, operating voltage between 1.8 and 5.5V. Real time clock module - usually communicates with the microcontroller through a serial port and transmits time information to the display unit through the microcontroller.

As a real-time clock module, its accuracy and stability are very important. Usually, the accuracy and stability of this real-time clock module mainly depend on an external 32.768kHz crystal as the running counting clock.

FC-135, as the red crystal unit of Epson, can be perfectly used in this thermometer solution because it has the following advantages in intelligent electronic thermometer solutions:

1. The frequency range is 32kHz~77.5KHz. FC-135 provides not only a frequency point with a fundamental frequency of 32.768kHz, but also an optional frequency point with a frequency range of 32kHz~77.5KHz, meeting the multifunctional design requirements of intelligent electronic thermometers.

2. The package size is 3.2X1.5X0.80mm, with a small size package, which is very easy to integrate and install in the timing module, saving the PCB board area of the thermometer every inch of land and money.

3. The ultra-low excitation power of 0.5 uW (1.0 uW Max) does not cause significant frequency shift during crystal resonance, making it very suitable for high-precision thermometer timing component design.

Multiple load capacitor options for 4.7pF, 9pF, and 12.5pF, making it convenient for customers to configure.

In summary, the timing module unit is combined with a 32.768kHz crystal FC-135 to form a real-time clock module unit, which enables the entire design to display timing information while displaying the measured body temperature, and is more accurate.

FC-135R internal resistance is 50K ohms<FC-135, 70K ohms