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Simple Audio Power Meter Using Duo LED

2015-01-08 14:46  
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Audio Power Meter indicates the amount of power that goes to a loudspeaker. This simpleaudio power meter circuituses dual-colour LED that shows green at an appliedpower levelof about 1 watt. At 1.5 watts it glows orange and above 3 watts it is bright red. The audio power meter circuit is connected in parallel with the loudspeaker connections and is powered from the audio signal. The additional load that this represents is 470 Ohm (R1//R3) will not be a problem for any amplifier. During the positive half cycle of the output signal the green LED in thedual-colour LEDwill be turned on, provided the voltage is sufficiently high. At higher output voltages, T1 (depending on the voltage divider R2/R1) will begin to conduct and thegreen LED will go out.

Simple Audio Power Meter Schematic Simple Audio Power Meter Using Duo LED

During the negative half cycle thered LEDis driven via R3 and will turn on when thevoltage is high enough. In the transition region (where T1 conducts more and more and ‘throttles’ the green LED as a result) the combination of red/green gives the orange colour of the dual-LED.

The resistors can be 0.25 W types, provided the amplifier does not deliver more than 40 W continuously. Above this power the transistor will not be that happy either, so watch out for that too. Because T1 is used in saturation, the gain (Hfe) is not at all important and any similar type can be used. The power levels mentioned are valid for 4-Ohm speakers. For 8-Ohm speakers all the resistor values have to be divided by two.

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