The LM3915 integrated circuit is used in an audio level indicator circuit that shows the audio signals strength graphically.
A flexible analog display driver integrated circuit intended for use in audio level visualizers and related applications is the LM3915.
Using an analog voltage input, it can drive up to ten LEDs, LCDs or other types of displays linearly.
LED VU meters are used in this article which are popular for music lovers as they visually display sound levels using LEDs.
Building one is easy with the LM3915 IC, which simplifies the construction process, allowing for a simple LED based VU meter.
Circuit Working:
Parts List:
| Category | Component | Quantity |
|---|---|---|
| Resistors | 1k | 1 |
| Preset 10k | 1 | |
| Semiconductors | IC LM3915 | 1 |
| LEDs | Green 5mm, 20mA | 2 |
| Yellow 5mm, 20mA | 6 | |
| Red 5mm, 20mA | 2 |
The circuit schematic above for the audio level indicator is simple to understand.
A digital integrated circuit is used to provide a visual display of sound level, or VU meter, may be seen when analyzing the pinout of the LM3915.
An audio signal is divided into ten parts using an integrated circuit, and each part is compared to an internal reference voltage.
It has ten output pins, each of which is connected to an LEDs.
A voltage divider controls the voltage level at these pins.
The audio signal is processed by a resistor network after being converted to DC voltage as soon as it enters the chip.
The voltage at each output pin varies in tandem with the voltage of the audio stream.
An output pins matching LED lights up when its voltage is higher than the reference voltage.
Formulas:
Based on the above circuit diagram, the following are some essential formulas and factors to take into account while creating an audio level indicator circuit with the IC LM3915:
Reference Voltage Vref:
This is controlled by the voltage divider network, which is made up of a preset 10k and a 1k resistor.
Vref = Vin × (Rpreset / Rpreset + R1k)
where,
- Vin Input voltage which is usually the voltage of the audio stream.
- Resistance of the preset 10k is represented by Rpreset.
- Resistance of the 1k resistor is represented as R1k.
LED Current Limiting Resistor RLED:
Utilizing ohms law determine the resistor value in order to limit the current flowing through the LEDs.
RLED = Vsupply−VLED / ILED
where,
- V supply is the supply voltage, which varies based on the circuit is 12V.
- VLED is the forward voltage drop across the LED, usually around 2V for red, green and yellow LEDs.
- Preferred LED current (usually 20mA) for ILED.
Segment Reference Voltage Vi:
Ascertain the voltage levels for every LED segment in the LM3915 is measured by formula:
Vi = Vref × i
where,
- Voltage for the i-th LED section is represented by Vi.
- i segment number, ranging from 0 to 10 for the LM3915.
Based on the supplied parts list, these calculations and factors should assist you in efficiently designing and calibrating an Audio Level Indicator Circuit with the IC LM3915.
How to Build:
To build a Simple Audio Level Indicator Circuit using IC LM3915 following are the connections steps mentioned below:
- Assemble all the required components as mentioned in the circuit diagram above.
- Connect pin 1 of IC LM3915 to 1st green LED cathode leg and continue the same method with pin 10 to pin 18 as shown in circuit diagram.
- Connect the anode leg of LEDs to positive supply of 12V.
- Connect pin 2 of IC LM3915 to ground.
- Connect pin 3 and pin 9 of IC LM3915 to positive supply of +12V.
- Connect pin 4 of IC LM3915 to one leg of preset .
- Connect pin 5 of IC LM3915 to audio input.
- Connect pin 6 to pin 7 of IC LM3915.
- Connect resistor R1s one end to pin 7 and the other end to pin 8 of IC LM3915.
- Connect pin 8 of IC LM3915 to center leg of VR1 preset.
Conclusion:
This is a simple way to create a visual audio level indication using the LM3915 IC.
It offers a convenient and effective way to monitor sound levels by efficiently transforming analog audio data into a sequence of LED illuminations.