PAGE 097 OF 150 · DISPLAYS & INDICATORS
LED Bar Graph Indicator
Bar graphs show levels as lit segments.
LED SYMBOLTriangle points from anode to cathode; the arrows show light leaving the part.
What a bar graph shows
A bar graph indicator uses a row of LEDs to show a level, such as volume, battery charge or tank contents. More LEDs lit means a higher value.
Two approaches
- LM3914 driver: reads an analogue voltage and lights up to ten LEDs in bar or dot mode. Its LED current is roughly 12.5 divided by one resistor value, so a 1.25 kilohm resistor gives about 10 mA.
- Microcontroller: read the sensor, then light about reading × 10 ÷ 1024 LEDs for a 10-bit input.
Colour the top LEDs red, the middle amber and the bottom green for quick reading.
REMEMBER
Pick bar mode for a level and dot mode for a position.Try it yourself
Sketch the circuit on paper first, calculate the values, then build it on a solderless breadboard using a low-voltage supply. Measure with a multimeter before you make anything permanent.
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