Arduino Report #12: Project 21--VU Meter

Additional Parts:

1. 220 Ohm Resistor x 10
2. 10k Ohm Resistor x3
3. 100k Ohm Resistor x1
4. BC548 Transistor x1
5. Push-to-make Switch x1
6. Electret Microphone x1
7. 10-Segment LED Bar Graph x1
8. 100 nF Capacitor x1

Time to Complete: 30 minutes

The VU Meter records the volume of sound picked up by the electret microphone and displays the intensity in the LED bar graph. There are two modes. The first displays the intensity in real time, and the second mode records only the highest intensity picked up by the microphone. The push-to-make switch is used to toggle between the modes. 

The most interesting part of the circuity in this project is in the wiring of the microphone and the transistor used to amplify the signal from the mic. The transistor is wired in a collector-feedback bias arrangement. In order to avoid a discreet switching of the transistor on an off, part of the voltage at the collector is used to bias the transistor. This lets the transistor amplify the signal from the microphone in a linear fashion. Clever. There are some subtleties in the program to ensure that the transistor bias does not permanently  illuminate the button bars of the LED. Other than that, the program is pretty straight-forward.


My eldest son helped me out with this video this time by clapping into the microphone as I filmed.

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