Transistor LED Bar Graph

by crazycircuitsfun in Circuits > LEDs

913 Views, 1 Favorites, 0 Comments

Transistor LED Bar Graph

Transistor LED Bar Graph 01 Product.jpg
Transistor LED Bar Graph 02 Step 01 Design the Circuit.jpg
Transistor LED Bar Graph - Sine Wave Input

This article shows a unique and controversial way of creating an LED bar graph display.

This circuit needs a high amplitude AC signal. You can try connecting a Class D amplifier to its input.

This circuit was designed and published many years ago based on the article shown here:

https://www.instructables.com/Hammer-Game-1/

Supplies

Components: TO3 heat sink - 1, TO3 BJT NPN power transistor - 1, small LEDs - 10, washers - 5. bolts - 4, nuts - 4, heat transfer paste, solder, matrix board/cardboard/wood, 100 ohm power resistors - 20, 10 ohm power resistor - 1, 10 kohm resistor - 2, 470 uF electrolytic capacitor - 2, 470 nF pillow capacitor - 2, in.

Tools: soldering iron, scissors, wire stripper.

Optional components: encasement/box.

Optional tools: multi-meter.

Design the Circuit

Transistor LED Bar Graph 02 Step 01 Design the Circuit.jpg

I have drawn the circuit in the PSpice student edition simulation software to save time.

The Rd resistor ensures that all LEDs are OFF when the Q1 transistor is disconnected (Rb1 set to the maximum value and no input AC signal is applied).

Simulations

Transistor LED Bar Graph 02 Step 01 Design the Circuit.jpg
Transistor LED Bar Graph 03 Step 02 Simulations - Transistor Voltage.jpg
Transistor LED Bar Graph 04 Step 02 Simulations - LED Current.jpg

Simulations show a low current output for the LEDs. This will not be true in real life if you are using a high-power transistor. Low power transistors have very limited maximum current output.

I varied the Rb1 potentiometer before simulating the circuit.

Make the Circuit

Transistor LED Bar Graph 05 Step 03 Make the Circuit.jpg

You can see that I made this circuit on a piece of cardboard to save money. I could have used a piece of plastic, wood, or even a matrix board.

I used low current, small 5 mA LEDs, and high power resistors. I also attached a high-power transistor and a heat sink.

Testing

Transistor LED Bar Graph - Testing

The testing shows how the variation in the variable resistor setting changing the number of LEDs that are turned ON.