Best Microphone Circuits for Connecting to RTB2004 Oscilloscope for Frequency Measurement

The discussion addresses the challenge of measuring audio frequencies generated by an embedded device using an RTB2004 oscilloscope. The device produces alert tones between 261 Hz and 987 Hz, and the goal is to verify these frequencies in assembled production units. Direct electrical connection to the oscilloscope is possible during development, but for assembled devices emitting sound, a microphone-based solution is sought. It is noted that microphones have limited bandwidth (typically up to 16 kHz) and may introduce signal distortion if not used properly. For frequency verification, a good quality microphone placed at an appropriate distance can capture the sound, and the signal can be amplified using a low-noise operational amplifier such as the TL081. Frequency measurement can then be performed by analyzing the waveform period on the oscilloscope. Among microphone types, electret microphones are commonly used for such applications due to their sensitivity and ease of integration. A practical recommendation includes using a microphone amplifier board, such as the Adafruit microphone amplifier (product 1063), which simplifies interfacing the microphone output to the oscilloscope. Alternative approaches like smartphone audio spectrum analyzer apps exist but are not suitable here due to test requirements restricting measurement to oscilloscopes only. Additional setup tips include using acoustic cones made of absorbent materials to direct sound towards the microphone and calculating frequency as the reciprocal of the waveform period measured on the oscilloscope.
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