I've been assigned a project that requires me to build a circuit that can recognize high frequency sound waves (16KHz - 20KHz). The setup is a electret mic to an amp to a high pass filter to my microcontroller (that determines the frequency of the wave). The input to the microcontroller is 0 - 3.3V.
My problem is getting the amp to work correctly. Because I only need to recognize a frequency of the sound wave I can use either an inverting or non inverting amplifier. Because the circuit will be battery powered i am using a single supply for my op amp (LM741CN) and not worry about the bottom part of the wave below 0V because my microcontroller can only accept 0-3.3V anyway.
I've been testing my amp with little success. To simulate input I am using a function generator. To simulate a battery I have a power supply set at 9V and plug the (-) terminal to common ground and the Vcc to the (+) terminal.
Here is my pinout for my chip (LM741CN):
33kohm resistor from pin 2 to 6 (inverting input to output)
Pin 3 (non inverting input) is grounded
Pin 7 (V+ Pin) to +9v of the power supply
Pin 4 (V- Pin) to ground (Negative terminal on the supply)
The two offset null pins I don't touch
Waveform from function generator through a 2.2kohm resistor to pin 2 (The inverting input pin)
So my gain should be 33/2.2, but instead of doing this the output from pin 6 gives me a voltage just below 9V. I've replaced the op amp several times with new ones (of the same type) but get the same results.
Ive noticed that when i slowly increase the power supply to the chip from zero to 9v the output from pin 6 goes from the original waveform signal (not even inverted) to being clipped from the bottom until it reaches the peak of the original waveform when the supply voltage is equal to the Vpp of the waveform. Past that voltage the waveform disappears completely and the voltage rises as a constant value that is about equal to the supply voltage.
These amps seem like such simple circuits, I have no idea what is wrong and I'm worried I've wasted so much time on some simple oversight like how I am handling the power supply.
I will be happy to provide pictures of my circuit on my breadboard or clarify anything.
My problem is getting the amp to work correctly. Because I only need to recognize a frequency of the sound wave I can use either an inverting or non inverting amplifier. Because the circuit will be battery powered i am using a single supply for my op amp (LM741CN) and not worry about the bottom part of the wave below 0V because my microcontroller can only accept 0-3.3V anyway.
I've been testing my amp with little success. To simulate input I am using a function generator. To simulate a battery I have a power supply set at 9V and plug the (-) terminal to common ground and the Vcc to the (+) terminal.
Here is my pinout for my chip (LM741CN):
33kohm resistor from pin 2 to 6 (inverting input to output)
Pin 3 (non inverting input) is grounded
Pin 7 (V+ Pin) to +9v of the power supply
Pin 4 (V- Pin) to ground (Negative terminal on the supply)
The two offset null pins I don't touch
Waveform from function generator through a 2.2kohm resistor to pin 2 (The inverting input pin)
So my gain should be 33/2.2, but instead of doing this the output from pin 6 gives me a voltage just below 9V. I've replaced the op amp several times with new ones (of the same type) but get the same results.
Ive noticed that when i slowly increase the power supply to the chip from zero to 9v the output from pin 6 goes from the original waveform signal (not even inverted) to being clipped from the bottom until it reaches the peak of the original waveform when the supply voltage is equal to the Vpp of the waveform. Past that voltage the waveform disappears completely and the voltage rises as a constant value that is about equal to the supply voltage.
These amps seem like such simple circuits, I have no idea what is wrong and I'm worried I've wasted so much time on some simple oversight like how I am handling the power supply.
I will be happy to provide pictures of my circuit on my breadboard or clarify anything.