Home > Circuit Bricks > Dot/Bar Display Driver
UPDATED:.21:05 21 October 2013
FUNCTION BLOCK
DESCRIPTION
  • This circuit will drive up to 10 LEDs that function as a moving dot or bar display
  • Ideal as a mini-voltmeter or an audio VU meter.
CIRCUIT DETAILS

The circuit is based around the very popular LM3914/5/6 - each having different steps in voltage for each LED.

VR1 sets the range of the display. VR1 at minimum, range = supply voltage. VR1 at maximum, range = half the supply.

Click on the IC number for the datasheet.

Circuit Diagram

Input

This can be any DC voltage up to the supply voltage. It can also be a rectified audio signal
Output

The outputs sink current so LEDs must be connected between +V (anode) and any output (cathode).

No resistor is needed in series with the LEDs.
MODIFICATION DETAILS

The circuit shown will produce a dot display. Connecting pin 9 to +V, the display will become a bar of LEDs.

The LED brightness is controlled by R1. Reducing the value (minimum 330 ohms) increases the brightness. In dot mode this is not a problem, but in bar mode, potentially all the LEDs could come on so it is advised at voltages of 9v and above, not to reduce R1 below 1K. The IC package will get hot if you do so take care.

This can be made very sensitive by increasing VR1 to 100K. Internally the resistor chain is made up of 10 x 1K resistors so to calculate the voltage range you can use the following:

Vmax = Vin x (10K / (VR1 +10K)

so when VR1 = 100K and the supply = 12v the range will be

Vmax = 12 x (10K / 110K) = 1.1v or 110mV per LED step.
PACKAGE DETAILS


Pin
numbers
 The LM3914 driver comes in an 18pin DIL package.
If possible use an IC holder so the IC can be removed easily and is not damaged from excessive heat while soldering.
LINKS TO PRROJECTS
Links to projects that use the LM3914/5/6
...Circuits/Survival Game

...Circuits/Audio VU Meter

...Circuits/Battery meter

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Written by Phil Townshend - 2008
www.edutek.ltd.uk - Working Electronics For Students & Teachers