A simple frequency to voltage (F/V) converter is a cool electronic circuit that changes a signal with different frequencies into a direct current DC voltage that matches that frequency.
These converters are used in many areas like tachometers, speedometers and industrial automation systems.
One popular component in this field is the LM331 which is a well known integrated circuit IC that works as both a voltage to frequency (V/F) and frequency to voltage (F/V) converter.
It is famous for being very accurate and flexible.
In this setup the IC LM331 acts as a frequency to voltage converter turning the input frequency into a voltage output that has a very straight relationship with the input frequency.
Here , the circuit runs on a 15V DC power supply.
This article will explore how an F/V converter works using the LM331 IC explaining important formulas and helping readers understand how to build the circuit step by step.
Circuit Working:
Parts List:
| Component | Value | Quantity |
|---|---|---|
| Resistors (1/4 Watt unless specified) | ||
| Resistor | 6.8k | 1 |
| Resistor | 68k | 1 |
| Resistor | 100k | 1 |
| Resistor | 12k | 1 |
| Resistor | 10k | 2 |
| Preset | 5k | 1 |
| Capacitors | ||
| Ceramic Capacitor | 0.01µF | 1 |
| Ceramic Capacitor | 100pF | 1 |
| Ceramic Capacitor | 470pF | 1 |
| Semiconductors | ||
| IC | LM331 | 1 |
This article explains a circuit that changes frequency into voltage using the LM331 integrated circuit.
The circuit mainly includes important parts like resistors, capacitors and the LM331 chip.
The LM331 works by taking a frequency signal and turning it into a voltage output.
The frequency to voltage conversion is attained by differentiating the input frequency using capacitor C3 and resistor R6 and feeding the resultant pulse train to the pin6 (threshold) of the IC.
Resistor R3 helps keep the circuit stable and properly biased.
There are also resistor R5 and preset VR1 that help set the reference voltage for the chip affecting the output voltage scale.
When the frequency signal is applied the LM331 generates a series of pulses and the duty cycle of these pulses changes based on the input frequency.
These pulses are then smoothed out by passing through capacitor C2 and resistor R4 resulting in a steady direct current voltage that matches the frequency of the input signal.
Formulas:
To build a Simple LM331 Based Frequency to Voltage Converter Circuit follow the below mentioned formulas:
The connection between the output voltage Vout and the input frequency Fin can be figured out with this equation:
Vout = K × Fin
where,
Kis the scaling factor dependent on R4, C2 and IC configuration.Finis the applied input frequency in Hz.
To determine the output voltage for a given frequency, use the ICs internal charge pump equations:
Vout = Iavg × R4
Iavg = (Vref / R5) × T
where,
Tis the pulse duration which is frequency dependent.Vrefis the internal reference voltage of LM331.
How to Build:
To build a Simple LM331 Based Frequency to Voltage Converter Circuit follow the below mentioned steps for connections:
- Gather all the components as shown in above circuit diagram.
- Connect pin 1 of IC1 LM331 through the output voltage by R4 resistor and capacitor C2 and GND
- Connect pin 2 of IC1 to GND through resistor R5 and preset VR1.
- Connect pin 3 and pin 4 of IC1 to GND.
- Connect pin 5 of IC1 to GND through capacitor C1.
- Connect one end of resistor resistor R1 to positive supply of 15V and other end to pin 5 of IC1
- Connect pin 6 of IC1 to Frequency input (Fin)through capacitor C3.
- Connect one end of resistor R6 to positive supply and other end to pin 6 of IC1
- Connect pin 7 of IC to GND through resistor R3.
- Connect one end of resistor R2 from positive supply and other end to pin 7 of IC1
- Connect pin 8 of IC1 LM331 to +15V positive supply.
Conclusion:
A Simple LM331 Based Frequency to Voltage Converter Circuit is an easy and efficient way to measure frequency and turn it into voltage.
This circuit works great for things like speed sensors, tachometers and systems that control industrial processes.
You can tweak the output voltage to fit your needs by changing the values of R4 and C2.
If you learn how this circuit works and do some calculations, you can adjust it for various frequency ranges and voltage outputs to suit your project needs.
References:
Precision voltage-to-frequency converter with 1-Hz to 100-kHz full scale frequency