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20 August 2011

Tachometer Circuit Using LM2907 LM2917 Frequency to Voltage Converter

This is a design circuit for tachometer circuit based on the LM2907 IC can be used to provide zero crossing datum to a digital system. At each zero crossing of the input signal the charge pump changes the state of capacitor C1 and provides a one-shot pulse into the zener diode at pin 3. The width of this pulse is controlled by the internal current of pin 2 and the size of capacitor C1 as well as by the supply voltage. This is the figure of the circuit;

Since a pulse is generated by each zero crossing of the input signal we call this a ``two-shot'' instead of a ``one-shot'' device and this can be used for doubling the frequency that is presented to the microprocessor control system. This electronic tachometer circuit project can be powered from a 12, 15 volt DC power supply circuit. Input can be from plus /minus 20 mV to plus/minus 28V. Pulse width is equal with (VCC/2)x(C1/I2) and the Pulse height is equal with VZENER.