Audio Wattmeter Circuit with LM3915

Posted on Feb 6, 2014

This sound wattmeter uses a row of colored LEDs as a scale to show the relative power output of your amplifier in watts. It is easy to be inserted into the speaker box. All you need is to hook a supply voltage to it. The value of R1 depends upon the impedance of the speaker being used. The table near the sound wattmeter diagram shows the necessary

Audio Wattmeter Circuit with LM3915
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values of R1. The supply voltage of the circuit is 12 20 volts/50 mA DC adapter. Take note that the LM3915 indicates only the positive swing of the signal. Anyway, by testing amplifiers it does not matter anyhow since a sine wave is normally used as a test signal. To test the circuit without using an actual speaker, you can connect a dummy resistor with a value of either 8 or 4 ohms.

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