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Small frequency meter and tachometer circuit with digital display

Published on Mar 16 2011 // Instrumentation and Tester Circuits

This is a very small volume of electronic production, but incredibly powerful and can be easily embedded installed in the instrument panel, suitable for lovers or for the transformation of old-fashioned home-made instruments,
  Only the two IC circuit, CD4069 for small signal amplification and shaping, AT90S2313 is a high-speed RISC microcontroller, its performance under the clock 8M over 51 performance in the 100M clock, in the circuit as a measurement, computation and display drivers. Most of the digital frequency meter with a "second gate" counts, which increased the measurement error at low frequencies, it can not display the decimal, and this circuit uses a dual pulse width and density measurement techniques, combined with high-speed floating-point operations, thus high accuracy, and can automatically convert range to show decimals. For example, the measurement results may be 0.543,261.4 so, use it to measure the alternating current frequency, you can see the results are generally slow in between 49.82-50.17 change, so this is very suitable for the circuit in the generator room for the AC power distribution frequency display.
  Circuit also has the speed measurement function, with a toggle switch conversion. Hall added, photoelectric, and electromagnetic sensors can detect speed, accurate measurement results as quickly, if coupled with an appropriate signal shaping circuit, you can even directly beside the gasoline engine to take high-voltage ignition signal, measured motorcycles, cars engine speed.
  Adding signals from the C3, if it is low frequency or low-speed signals, skip the C3 input would be more effective, adjustable resistance measurement is used to adjust the sensitivity of P1, S1 for the frequency – speed measurement conversion, showing a 0.56 in. using a 4-bit digital tube LED common cathode.

Small frequency meter and tachometer circuit with  digital display 1

Small frequency meter and tachometer circuit with  digital display 2

 Small frequency meter and tachometer circuit with  digital display 3

Specifications: Supply voltage 8-15V DC
       Supply current 100mA
       Input Sensitivity 100mV-5V
       Input impedance 500KO
           Frequency range 0.4-1000000Hz
       Speed range of 20 r / min -1000000 rev / min
  1. Because the input impedance is high, so pay attention to anti-interference, if necessary, reduce the input impedance.
  2. DC blocking capacitor C3 is used when measuring low-frequency and low speed, skip the C3 input will be more effective.
  3. Strong power in the measurement, to increase isolation, and pay attention to anti-interference shielding.
  4. Directly from the high voltage side of ignition gasoline engine sensor signal measurements taken when the engine speed, to add a suitable signal shaping circuit, but also pay attention to anti-interference.
  5. The use of 4-bit digital control, it can only display 4 digits, more than 9999 results, retaining only the high 4 digits, with numbers behind the decimal number that rate. Such as "6666" for 6666, "6666." There is a decimal point, that 6666X10 1 , "666.6." there are two decimal places, that 6666X10 2 , and so on, but the number of decimal places that the real numbers, this method does not such as "50.12."
  6. Circuit starts to display "", So if frequent use of "", Said the environmental interference, shielding should be added to the circuit.
  The following are components and the PCB layout diagram should be noted that PCB surface map is read from the TOP view of the past, if you look at it from the BOTTOM side should, in turn, be sure to find out imitation.