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LED Bar Graph With Transistors

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LED Bar Graph With Transistors
LED Bar Graph With Transistors - Circuit Diagram

An 11 Element LED Bargraph

LED Bargraph built on a solderless breadboard Transistors drive eleven LEDs in an analog bar

There are a number of integrated circuits and modules available that are designed specifically for building led bar graph circuits but if your junk box looks anything like mine then you probably don't have one. What if you want to build a bar graph today and don't have the right chip?

I always have a small stock of transistors, diodes and resistors to hand just like most other hobbyists. We have them because they are easy to obtain, cheap as chips and useful for all kinds of things. So if I can build something out of these basic components then I can get the circuit working in an hour or two without waiting for an online order to arrive. Why don't you give this one a try.

Potentiometer for simulating input Potentiometer input simulator

To demonstrate the bargraph circuit you can use a potentiometer control. A 5kΩ or 10kΩ potentiometer can be wired across the input voltage reference to provide a variable input voltage to the bargraph. If you have a control with printed circuit board terminals like the one I used then the pins will probably fit into the breadboard without modification.

If the terminals on your potentiometer are too wide then you can file them down a little using a flat needle-file.

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LED Bar Graph With Transistors
LED Bar Graph With Transistors - Circuit Diagram

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Comments (5)

Topic: LED bar graph with transistors
Full StarFull StarFull StarFull StarHalf Star 4.5/5 (5)
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Wilame (Brazil) says...
Wow, its amazing. Congratulations for to share with us.
13th July 2020 5:40pm
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Harold Lacadie (US) says...
Works as advertised! However I could only get it to work is with a LM358 which is what the LM324 is based on. Really cool circuit!
26th June 2020 12:04am
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Derek Jacobsen (US) says...
Hi Tim, I tried building this circuit as a fun home project but am having some trouble getting it to work. Are the positive and negative ves the positive and negative terminals of one battery or two batteries with one connected negatively. Also im not sure how the physical hardware wiring of the potentiometer works. Any help you could give me would be much appreciated.
19th November 2019 7:58pm
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Tom (US) says...
As to the battery question, it looks like one nine volt battery with the + connected to the top (+) and the - connected to the ground which is marked -ve. Regarding the 10,000 ohm potentiometer question the typical potentiometer has three terminals. The center terminal is shown in the center and is connected to the hollow o by an arrow. This terminal is where the knob changes the resistance relative to the two other terminals. (I realize it has been years since this question was asked but this ... Read More
12th December 2023 11:45pm
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Tim Ralston (US) says...
Simply perfect! designs like these always save the day when you can pop it together right out of the parts box, especially if you need to knock together a last minute gadget. Being able to say "yes I can do that in a couple hours" vs a couple days, always keeps me employed.
Thank you, Thank you, Thank you, for your generous sharing.
20th April 2017 4:18am

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