LM3916N: build a 10-LED level display

One chip turns an analog voltage into a moving point or bar of ten LEDs. Build this 5 V test circuit first, then learn what must change to display an audio signal.

What the chip does

The LM3916 compares the voltage on signal input pin 5 with ten built-in thresholds. As the voltage rises, its ten current-regulated outputs light LEDs in sequence. The thresholds are spaced for a VU-style display, not a linear voltmeter. Pin 9 selects dot mode (one LED) or bar mode (all LEDs up to the level).

LM3916N: build a 10-LED level display
Functional overview; the numbered wiring list is the build instruction.

Parts and a 5 V supply

One LM3916N in 18-pin DIP, ten ordinary red or green LEDs, one 1.2 kΩ resistor, one 10 kΩ potentiometer, one 100 nF ceramic capacitor, a breadboard, and a regulated 5 V DC supply. Allow at least 150 mA from the supply for the ten-LED bar. An optional 10 µF electrolytic near the LED supply helps with long supply wires.

Wire it, one group at a time

LM3916 PDIP-18 top view, redrawn from the manufacturer connection diagram. Outputs are numbered by LED order, not by consecutive package pins.
LM3916 PDIP-18 top view, redrawn from the manufacturer connection diagram. Outputs are numbered by LED order, not by consecutive package pins.
  1. With the notch at the top, count down the left side from pin 1 to pin 9, then up the right side from pin 10 to pin 18. Use the separate top-view pinout below.
  2. Connect pin 2 (V−) and pin 4 (divider low) to ground. Connect pin 3 (V+) to +5 V. Put the 100 nF capacitor directly between pins 3 and 2.
  3. Join pin 6 (divider high) to pin 7 (reference output). Put the 1.2 kΩ resistor between pin 7 and pin 8 (reference adjust); connect pin 8 to ground. Pin 7 is now approximately 1.25 V, the top of the display range.
  4. Connect the two outer ends of the 10 kΩ potentiometer between pin 7 and ground. Connect its middle wiper to pin 5 (signal input). Turning the knob now sweeps the input from about 0 to 1.25 V.
  5. Connect the anode (long leg) of each LED to +5 V. Connect each cathode (short leg / flat side) to its output: LED 1 to pin 1, LED 2 to pin 18, then LEDs 3–10 to pins 17–10 in order. Do not add individual LED resistors: the LM3916 regulates their current.
  6. Leave pin 9 open for dot mode. With power off, link pin 9 directly to pin 3 for bar mode; never leave a loose mode wire where it can touch other pins.

First power-up and what to expect

Start with the potentiometer fully toward ground. Apply 5 V and turn it slowly. In dot mode one LED should move from the low end toward LED 10. In bar mode the lit bar grows. Pin 7 should measure roughly 1.25 V to ground. The 1.2 kΩ resistor sets roughly 10–13 mA per lit LED; it is not the reference voltage divider by itself. If nothing lights, check the notch direction, LED polarity, common ground, and pin 9. If all LEDs are always on, check that the pot wiper really goes to pin 5 and not directly to +5 V.

Turning it into an audio VU meter

An audio waveform swings above and below ground; this test circuit expects a positive level voltage. A raw audio output on pin 5 will therefore not make a calibrated VU meter. Add a suitable rectifier and smoothing/averaging stage, then scale its DC output into the 0–1.25 V input range. A simple diode alone loses small signals to its forward-voltage drop, so the precision rectifier/average-detector circuits in the datasheet are a better starting point. Take the signal from a low-level audio output, not directly from a power amplifier speaker terminal. Share signal ground with the LM3916 supply.

The stocked part and source

The stocked LM3916N is new old stock in DIP-18. Its maker has not been verified from a package marking, so the Texas Instruments LM3916 family datasheet is used as a functional reference, not proof of this lot’s provenance.

View the LM3916N product · LM3916 datasheet