A simple F/V converter is a useful circuit that converts signals of different frequencies into corresponding DC voltages, and people use it in many applications, including tachometers, speedometers and industrial machines.
LM331 is popular IC for this and it can do both V/F and F/V and it is very accurate and very flexible, here LM331 works as F/V converter and it change input frequency to voltage.
Also, voltage goes up when frequency goes up and the circuit uses 15V DC power.
Therefore, this article for LM331 Based Frequency to Voltage Converter Circuit show how F/V converter works using LM331 IC and it also give formulas and easy steps to make this circuit.
Circuit Working:
Parts List:
| Components | Values | Quantity |
|---|---|---|
| Resistors (All resistors are 1/4 watt unless specified) | 6.8k | 1 |
| 68k | 1 | |
| 100k | 1 | |
| 12k | 1 | |
| 10k | 2 | |
| Preset 5k | 1 | |
| Capacitors | Ceramic 0.01µF | 1 |
| Ceramic 100pF | 1 | |
| Ceramic 470pF | 1 | |
| Semiconductors | IC LM331 | 1 |
This article show circuit that change frequency to voltage using LM331 IC and main parts of this circuit are resistors, capacitors and LM331 chip.
Here, LM331 take frequency signal and give voltage output and the conversion happen by using capacitor C3 and resistor R6 and they make pulse signal go to pin 6 of IC.
Then resistor R3 keep circuit stable and give right bias and resistor R5 and preset VR1 set reference voltage, and this change output voltage level.
When frequency signal come then IC LM331 make pulses and then pulse duty cycle change with frequency.
Hence, pulses go through capacitor C2 and resistor R4 to become smooth DC voltage and this voltage match input frequency
Formulas:
To make simple LM331 F/V converter we need to use these formulas:
Output voltage (Vout) and input frequency (Fin) is link by:
Vout = K × Fin
where:
- K is scale factor and it depends on R4, C2 and IC setup.
- Fin input frequency in Hz.
To find Vout using ICs charge pump the formula is:
Vout = Iavg × R4
Iavg = (Vref / R5) × T
where:
- T is pulse time and it depends on frequency.
- Vref is IC LM331s inside reference voltage.
How to Build:
To build a LM331 Based Frequency to Voltage Converter Circuit follow the below mentioned steps for connections:
- First, gather all parts shown in diagram.
- Next, pin 1 of LM331 connect to output line using R4 and C2 and then to GND.
- After that, pin 2 connect to GND with R5 and VR1 preset.
- Then pin 3 and pin 4 connect to GND.
- Also, pin 5 connect to GND using capacitor C1.
- Further, one side of R1 go to +15V and other side to pin 5.
- Now pin 6 connect to input frequency Fin using C3 and one side of R6 go to +15V and other side to pin 6.
- Then pin 7 connect to GND with resistor R3 and R2 connect from +15V to pin 7.
- Finally, pin 8 connect to +15V.
Conclusion:
To conclude, Simple LM331 Based Frequency to Voltage Converter Circuit is easy and works well, it is good for speed sensors, tachometers and industrial systems.
Change R4 and C2 to adjust output voltage and understand circuit and use formulas to make it fit different frequency and voltage needs.