Introduction: LED High & Medium Pass Filters

We created high and medium pass filters to cause LED's to brighten and dim depending on the frequency put into the circuit. When higher frequencies are put into the circuit, only the green LED will light up. When the frequency put into the circuit is in between the high and medium frequencies both LED's will be lit up. As the frequency decreases the green LED will dim and the yellow LED brightens. Once the frequency hits the cutoff point of the high pass filter, only the yellow LED will be lit up. As you keep decreases the frequency input, the yellow LED will continue to dim until it hits its cutoff frequency. You can add to this circuit by having a low pass filter as well to have an third LED light up when lower frequencies are put in. You can also go even further than this and hook the filters up to a strip of LED lights and an audio port, to cause all of the LED's in the strip to flash certain colors as the frequency changes due to music.

Step 1: Schematic & Set Up

[* explain in broad terms the different elements of your circuit - inputs, gain stage, filters - and how they connect ]

Step 2: Parts List

1 - 10uF capacitor

1 - 0.047uF capacitor

1 - 0.47uF capacitor

1 - .01uF capacitor

1 - 1n4148 diode

1 - 50K pot.

1 - 2n3904 transistor

2 - 2n3906 transistor

3 - 100 ohm resistor

2 - 10K ohm resistor

2 - 1K ohm resistor

1 - 2.2K ohm resistor

1 - 150 ohm resistor

1 - 4.7K ohm resistor

1 - 270 ohm resistor

2 - different colored LEDs

Step 3: Construction

Follow the schematic given schematic and built the circuit part by part. We started by building the first third of the circuit which is the amplifier. Then, we added on the first filter which is the high pass filter. Finally, we added on the last third of the circuit which is the medium pass filter. Hook up the beginning of the circuit to an input where you can alter the frequency put into the circuit.

Step 4: Completed Project

Now you will be able to change the brightness of each LED but increasing and decreasing the frequency at the input. [*