Beat-Driven Bird
by Kaylah Janis
Project Overview
This project creates a mechanical bird that bobs its head to the beat of music. Using this circuit, you can get a motor to drive something to the beat of music. The circuit takes an audio input and filters the signal with a low-pass filter to isolate the musical beats. The signal from the low-pass filter is rectified with a diode, and a capacitor is used to produce a DC voltage proportional to the intensity of the beats. The filtering stage helps the circuit detect beats instead of reacting to every detail of the music. The resistor and capacitor values of the low pass filter can be adjusted depending on the music and the frequency range you want the bird to respond to.
The filtered and rectified signal is sent to a differential comparator, which compares it to a threshold level set by resistors in a voltage divider. By setting the threshold level, you can control the sensitivity of the motion, as only beats or parts of a song strong enough to exceed the threshold will trigger the output. In this design, the threshold that works is around 400 mV. When the signal exceeds the threshold, the comparator outputs a 5V, otherwise it outputs 0V. Using a comparator allows the motor to move to the beats of the music and not as much to musical fluctuations. as the motor only gets voltage when there is a beat.
The comparator output is connected to a N-Channel MOSFET which acts as a switch to control the 15V supply to the motor (The motor requires 15V to work). This functions as a transistor switch circuit. The comparator output is sent to the gate of the MOSFET, the motor is connected 15 V and to the drain side of the MOSFET, and the source side of the MOSFET is grounded. A resistor is connected between the gate and the source to ensure that the motor stays off when no beat is present. When comparator sends 5V to the MOSFET gate, the MOSFET turns on and lets current flow through the motor from a 15V supply, so that the motor moves. This allows the motor to power on when there are beats in the music. The motor moves a stick that can be decorated like a bird, causing the bird to bob in sync with the music. You can add eyes, wings, feathers or other decorations, and use a stand to support the motor assembly. A rubber band or elastic string is attached between the stick bird and the stand so that the bird springs back upward after each bob.
Get ready to mosh with your dancing bird.
Tools and Materials
- DC Motor (15 V)
- MOSFET (IRL520N - Enhancement N-MOSFET)
- Voltage Comparator (LM- 311)
- Diode (IN4007 Si Diode)
- Variable Resistor Box (at 17k Ω)
- Variable Capacitor Box (at 0.01 uf)
- 4.7 nf capacitor
- Various Resistors ( 1 M Ω , 10kΩ, 1k Ω, 499 Ω)
- Audio Jack
- Stick
- Decorations for Bird
- Stand
- Elastic
