Tuning Fork Audio Amplifier v2

Goal: Determine most effective combination of input sensor and amplifiers.

Inputs:

• Microphone
• Transmissive IR sensor
• Reflective IR Sensor

Outputs:

• Square wave via test points
• Sine wave via headphone jack

Op-amps implement 8th-order active butterworth low-pass filter with corner frequency of 440 Hz and gain of 60 dBV.

Op-amps implement 2 stage unfiltered amplifier with gain of 60 dBV.

Input is selected from 3 possible sensors with DIP switches

Headphone jack L and R channels have buffer amplifier with volume knobs. Minimum gain is less than 1. Output is AC-coupled.

Left channel signal is selected from these two options by DIP switch:

• Active filter output
• Unfiltered amplifier output

Right channel signal is selected form these two options by DIP switch:

• Halfway through active filter
• Halfway through unfiltered amplifier

Comparators produce square waves from the following signals:

• sensor output
• halfway through active low-pass filter
• halfway through unfiltered amplifier
• outut of unfiltered amplifier

Power:

• 5 V from micro USB
• 2.5 V from LDO

See attachment for block diagram and filter design report.

References:

• https://www.instructables.com/Tuning-Fork-Oscillator/
• https://www.instructables.com/Tuning-Fork-Clock/