In this article I am going to discuss about vu meter circuit using lm 3915 IC. A VU meter can be described as an audio visualizer circuit. This circuit activates LED’s connected to it according to intensity of sound / signal detected. These circuits are commonly used with audio systems and amplifiers to display the audio spectrum. The attached LED’s glow with the format of tunes that makes the devices look cool.
lm3915 IC Pinout
LM 3915 is a monolithic IC with 18 pins. This IC senses analogue signal levels and drives 10 LED’s accordingly.
| Pin 1 | Led 1 | |
| Pin 2 | – V | Ground |
| Pin 2 | + V | VCC
3 – 25 v |
| Pin 4 | RLO | Low voltage level
for potential divider |
| Pin 5 | Signal | Analogue signal
Input |
| Pin 6 | RHI | High voltage level
for potential divider |
| Pin 7 | REF OUT | Reference output
voltage for led ( Current limiting ) |
| Pin 8 | REF ADJ | Adjust pin for
Voltage reference |
| Pin 9 | Mode | High and low
Selects dot and Bar mode |
| Pin 10-18 | Led 2 – 10 | LED’s 2 – 10 |
Components Required
Components required for vu meter circuit using lm 3915 IC are –
- IC lm 3915 x 1
- LED’s x 10 ( any colour )
- 22 µF / 25 v capacitor x 1
- 1 kΩ25W resistor x 2
- Small switch X 1
- 5 / 9 V battery x 1
- 18 pin IC base
- Breadboard / Vero board
Circuit Diagram
VU meter circuit using lm 3915 IC is shown below
Connections
You can make connections according to your convenience. Connections to all the pins of IC are described below.
- Make connections in IC base. IC should be mounted at last. Its because the heat generated by the soldering process damages the IC.
- Take LED’s of any colour and connect their negative terminals to pin 1 and 10 – 18 of the IC. As shown in the circuit.
- The positive terminals of all the LED’s are connected to positive terminal of the battery.
- Connect pin 2 of the IC to negative terminal of the battery.
- Pin 3 is connected to positive terminal of the battery.
- Pin 4 is again connected to negative terminal.
- A capacitor of 25 micro farad is connected between pin 3 and 4. That is parallel to the battery.
- Audio signal is provided at pin number 5.
- Pin 6 and 7 are shorted and 2 resistors of 1 KΩ ( in series ) is connected to them. The other side of resistor is connected to pin 4 is shown in circuit.
- Pin 8 is connected to the junction between 2 series resistor.
- 9th pin is connected to the positive 5v with a switch in series.
Working of VU meter circuit using lm 3915 IC
LM 3915 is a monolithic display controller IC with 18 pins. This IC senses analogue signal levels and drives 10 LED’s accordingly.
The main controller of the IC gets activated by 5v DC input. The operating voltage range of IC lies between 3v to 25 v. DC input at pin 2 ( VCC ) turns on the IC for its operation.
The input signal at pin 5 is in the form of musical or audio signal. The range of audio signal can vary from 1.2 to 12v. According to this voltage, a reference voltage is set in the circuit using resistors.
We already know that the IC has 2 operating modes that can be selected using pin 9 of the IC. High and low signal inputs selects dot and bar mode.
Author
Akash Sharma
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