Small digital display frequency meter, tachometer, DIGITAL FREQUENCY METER
Keywords: smart digital display frequency meter, speedometer
Small digital display frequency meter, speedometer
Be
This is a very small electronic production, but the function is very powerful, which can be very easy to embed the installation on the instrument panel, suitable for the enthusiasts to make some or used to transform the vintage instrument
The circuit only uses two integrated circuits, and the CD4069 is used for amplification and shaping of small signals. The AT90S2313 is a high-speed microcontroller of a streamlined instruction. Its performance exceeds the performance of the 51 series in the 8M clock, in the circuit Working as measurement, operation and display drive. Most of the number of digital frequency courses use a "second gate" count, so the measurement error is increased at low frequencies, and the decimal is not displayed, and the circuit uses the pulse width and density dual measurement technology, supplemented with high speed floating point operations, and thus High measurement accuracy, and automatically converts the range, showing the decimal. For example, the results of the measurement may be 0.543, 261.4, etc., using it to measure AC frequency, you can see the results in slow change between 49.82-50.17, so this circuit is ideal for an electric power in the generator and distribution room. Frequency display.
The circuit also has a speed measurement function, converted with a dial switch. In addition to the sensor such as Hall, photoelectric, electromagnetic, measure the speed, the measurement results are equally accurate, if you add a proper signal shaping circuit, you can even take a signal next to the ignition high voltage line of the gasoline engine, measure motorcycle, car Engine speed. Signal is added from C3. If it is a low frequency or low speed signal, skip C3 input will be more efficient, the adjustable resistor P1 is used to adjust the sensitivity of the measurement, S1 is used for frequency-speed measurement conversion, displayed is a 0.56 inches 4-digit LED common yin digital tube.
Technical indicators: power supply voltage 8-15V DC power supply current 100mA input sensitivity 100mv-5V input impedance 500KΩ measurement range 0.4-1000000Hz speed range 20 rpm / min - 1000000 rp / division
Note: 1. Because the input impedance is high, it is necessary to pay attention to anti-interference, and if necessary, it can reduce the input impedance. 2. Capacitor C3 is used in the flow of flow, and when the low frequency or low speed is measured, the C3 input will be more efficient. 3. When measuring power, add isolation, and pay attention to anti-interference shielding. 4. When the induction signal is taken directly from the gasoline engine ignition, the engine speed is measured, it is necessary to add a suitable signal shaping circuit, but also pay attention to anti-interference. 5. Due to the use of 4-bit digital tube, only 4-bit valid numbers can only be displayed, and the result of more than 9999 is only retained with a high 4-bit effective number, and the magnification is represented by the number of decimal points behind the number. As "6666" indicates 6666, "6666." There is a decimal point, indicating 6666x101, "666.6." There are two decimal points, indicating 6666x102, pushing in this class, but the decimal point in the number indicates the real number, not applicable, such as "50.12". 6. "0.0.0.0.0." Is displayed when the circuit starts, so if "0.0.0.0.0." Appears in use, indicating that the environment interference is large, and the circuit should be added to the circuit.
The following is a component layout and a PCB map, you need to note that the PCB map is a view from TOP. If you look from the bottom, you must make it clear when you are imitation.
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