Introduction

Frequency-to-voltage converter circuits, or F-to-V or FVC circuits, are widely used to measure speed and monitor flow rates and sensing positions. These circuits transform input signal frequencies into corresponding voltage outputs, facilitating the control and processing of actuators. The LM331 Frequency to Voltage Converter Circuit, featuring an LM331 Precision Voltage to Frequency Converter/Frequency to Voltage Converter IC by Texas Instruments, is capable of translating input signal frequencies into data suitable for microcontrollers or embedded systems. It accepts both sine waves and square pulses, with a preference for square pulses and PWM signals, making it practical for frequencies up to 10KHz, generating proportional voltage outputs.

IC LM331

The LM331 series integrated circuits (ICs) are well-suited for cost-effective applications and simple circuits. They are handy for analog-to-digital conversion, precise frequency-to-voltage conversion, linear frequency modulation/demodulation, and various other functions. These ICs are versatile and can operate on a single supply or split supply configuration, making them compatible with as low as a 5V DC power source. Despite their functionality, they have a low power consumption of just 15mW when powered by 5V DC. With the appropriate external components, this IC can effectively handle frequencies ranging from 1 Hz to 100 KHz. It is available in an 8-pin PDIP package.

Pinout Design

Pin 1 (IOUT) is the current output, Pin2 (IREF) is the reference current, Pin3 (FOUT) is the frequency output, Pin4 (GND) is the power supply ground, Pin (RC) is the R-C filter input, Pin6 (THRESH) is the threshold input pin, Pin7 (COMPIN) is the comparator input pin, and Pin8 (VS) is the supply voltage pin.

Circuit Diagram

Required Components

•  470pF Unpolarized capacitor, small symbol C1 C_0805_2012Metric
• 0.01uF Unpolarized capacitor, small symbol C2 C_0805_2012Metric
• 1uF Polarized capacitor, small US symbol C3 C_0805_2012Metric
• +15v Generic screw terminal, single row, 01x02, script generated (kicad-library-utils/schlib/autogen/connector/) J1 TE_282834-2
• Freque. Input Generic screw terminal, single row, 01x02, script generated (kicad-library-utils/schlub/autogen/connector/) J2 TE_282834-2
• Vout Generic screw terminal, single row, 01x02, script generated (kicad-library-utils/schlib/autogen/connector/) J3 TE_282834-2 10k Resistor, small US symbol R1,R3 R_0805_2012Metric
• 6.8k Resistor, small US symbol R2 R_0805_2012Metric
• 68k Resistor, small US symbol R4 R_0805_2012Metric
• 12k Resistor, small US symbol R5 R_0805_2012Metric
• 100k Resistor, small US symbol R6 R_0805_2012Metric
• 5k Potentiometer RV1 Potentiometer_Bourns_3266Y_Vertical
• LM331N_NOPB U1 DIP794W45P254L959H508Q8

Configuration and Operation

Capacitors and resistors are the external components required to configure a fully operational frequency-to-voltage converter. An input pulse applied to Fin undergoes differentiation via a network comprising capacitors and resistors. When the negative edge of this differentiated signal reaches the Threshold Input Pin (pin 6), it triggers the timer circuit through the input comparator. Using the following calculation, you can compute the average current exiting the Current Output Pin (pin 1).

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