Starting from scratch

[MC_locklin]

My challenge is to design and build a circuit that will take an audio input and convert it to a visual display.

The device will have 3 LEDs and each LED will represent a different frequency,
say
Less than 1kHz
Between 1kHz and 5kHz
Above 5 kHz

So whenever the device picks up a sound it will turn on the appropriate LED.

It only has to pick up a clear sound with a fixed frequency, nothing too complex.

I was wondering if you could give me a few ideas on how to approach this, any help you could give would be much obliged.

Thanks

 

[duke37]

You need three filters.
A low pass filter for under 1kHz
A band pass filter for 1kHz to 5kHz
A high pass filter for above 5kHz

The band pass filter will be the most difficult with a 5:1 frequency ratio but you may be able to assume the signal is between 1kHz and 5kHz if the upper or lower filters are not activated.

The sharpness of the filters will depend on your desires.
Active filters using op-amps would be the way to go.
Each filter would need a diode detector to switch the led.