The LM3915 is a Logarithmic Display Driver IC commonly used in visualizing audio signals. It can drive both 10-segment Bar LED and Dot Matrix LED. The IC also allows the reference voltage and LED current to be easily programmed based on the application by selecting the right value of resistors.
Pin Configuration
| Pin Number | Pin Name | Description |
| 1 and 10 to 18 | LED1, LED2, LED3…..LED10 | The 10 LEDs which has to be controlled is connected to these pins |
| 2 | V- / Ground | Ground pin of the IC |
| 3 | V+ / Vcc | Supply Voltage (3-18)V |
| 4 | RLO | Low level voltage for potential divider |
| 5 | Signal | Analog signal Input pin based on which the LED is controlled. |
| 6 | RHI | High Level voltage for potential divider |
| 7 | REF OUT | Output Reference Voltage for LED current limiting |
| 8 | REF ADJ | Adjust pin for voltage reference |
| 9 | Mode | Select between Dot/Bar Mode |
Specifications
- Analog Controlled LED Driver IC with Logarithmic output
- LED incremented by one step for every 3dB
- Monitor upto 30dB using 10 LEDs
- Number of controllable LEDs: 10
- Operating Voltage: 3V to 25V
- Reference Voltage: 1.2V to 12V
- LED sink current: 1mA to 30mA (programmable)
- Both Dot/Bar mode available
- Available in 18-pin DIP package
Note: Complete Technical Details can be found at the LM3915 datasheet given at the end of this page.
Where to use LM3915
The LM3915 is an audio-controlled LED driver IC, meaning it can control (turn on or off) 10 LED lights based on an analog input voltage of the audio signal. As we know the voltage value of an audio signal varies based on the amplitude of the signal, this amplitude is directly proportional to the loudness of the audio signal. Thus by making the LEDs glow with respect to the amplitude of the audio signal will help us visualize the audio signal. This IC eliminates the need for microcontroller and programming and also reduces the hardware required to control 10 LEDs.
The analog input voltage of the audio signal can vary from 1.2V to 12V and the LED current can be limited by simply using a resistor divider network on pin 7 (Ref Out). The IC increments the LED by one step for every 3dB rise in Audio signal, thus for 10 LEDs the IC can monitor upto 30dB audio signal. Further the IC can also be cascaded to monitor upto 90dB of audio signal by using 30 LEDs.
Since the LEDs can be controlled without any flickering and flawlessly with equal brightness these ICs are commonly used in visual alarms and other metering/monitoring applications. So, if you are looking for an IC to driver your bar LED lights or other sequence of 10 LED then this IC might be of interest to you.
How to use a LM3915
The LM3915 can be easily operated with very little additional components. The complete working of the IC and how do use it is discussed in the video linked at the bottom of this page. A sample application circuit from the LM3915 datasheet is given below.
As you can see we only require the LEDs and two resistors as additional component to use this IC. The IC can operate between 3V to 25V. The Audio signal maximum voltage can be as high as 12V or as low as 1.2V. Based on this voltage, the reference voltage has to be set in the circuit using the resistors R1 and R2. Let’s assume that the maximum voltage level from our audio signal is 3.6V and the minimum voltage is 0V. In this case, the pin RHI and REF OUT should be supplied with 3.6V and the pin RLO should be supplied with 0V. The IC also allows the designer to set the required current that should flow through LED. Both the LED current and the reference voltage can be set with the Resistor R1 and R2 using the below formulae
Applications
- Audio visualization circuits
- Crude Battery level indicators
- Low cost monitor devices
- Digital gauges
- Electronic displays
- Fade bars
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