dig:micpreamp
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+ | ===== Electret microphone amplifier ===== | ||
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+ | We'll build an amplifier that amplifies the microphone signal enough that the AVR32 ADC can convert the signal with sufficient resolution to be able to measure sound volume. | ||
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+ | From the datasheet we see that the LM324 can operate with a supply voltage down to 2.6V so we are OK with a 3.3V Vdd supply. | ||
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+ | The amplifier circuit uses the microphone JFET to generate the first voltage Vmic from the 6.8k resistor Rmic. Then a blocking capacitor Cmic=10uF blocks the DC level from Vmic and couples it to the opamp positive input V+. The DC level of V+ is set by the resistive divider from the two 56k resistors to 3.3V/ | ||
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+ | The illustration below shows a sketch of this amplifier schematic, along with the bypassed power supply for the servo motor. | ||
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+ | {{dig: | ||
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+ | The [[http:// | ||
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+ | By trying different resistor values, we find that we get the largest signal using a 7kOhm resistor in source configuration, | ||
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+ | The pinout of the quad opamp is below. The power supply pins are in the middle on opposite sides. You can remember these as "low is high" since the positive supply is on pin 4 and negative on pin 11. Each opamp follows the pattern "+ - out" from the middle to the corner. | ||
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+ | And also, here's how it looks after wiring up the microphone preamp: | ||
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dig/micpreamp.txt · Last modified: 2024/02/29 07:28 by 127.0.0.1