OP AMPS + ELECTRET MIC = SOUND DETECTION

This circuit i used to gauge the overall amplitude of noise in a room. i used to detect the volume level and output a analogue signal to control a project. It uses a electret Mic to transduce the sound to voltage then amps it with the op amps.

I worked out this one

Probably better and easier:

This opamp seemed to work better than the lmn356 I got more gain and the output numbers didn’t fluctuate as much. The circuit is just two op amps in series the first cleans the ac voltage from the mic with a capacitor and then "rides" it on a 2.5 volt dc current so you get 0 as the base value and not a negative number. The second takes that signal and grounds the base voltage and then amplifies it so you get an output value of 0 to ~ 4v if you yell into the mic. The basics of an op amp is a comparator circuit, the circuit takes two positive voltages into an inverted and non-inverted input then compares them. If the non-inverted voltage is higher then it saturates to a positive voltage if the inverted is larger then it saturates negative or “low”. The key to the amplifier circuit is a feedback resistor (R2, R3) between the output of the circuit and the inverted input. This sends back a “dampening” voltage to the input not allowing it to fully saturate and controls the output voltage. This signal is ok but there are kits out there that give you a great range (the super snooper kit) and you don’t have to worry about trouble shooting them, but this opamp gives numbers that seem to be smoother than other op amp circuits so it worked well for the microcontroller application.

OP AMPS + IR = HEART RATE SENSOR

The heart rate IR sensor functions by gauging the oxygen content of your capillaries. The IR signal is absorbed and reflected according to the amount of oxygen in your blood stream, this way you can get your pulse rate and blood oxygen levels.

click here to enlarge

The circuit is based around three high pass filters (click here to see tagged schematic). The first uses a large blocking capacitor to get the dc signal out in conjunction with two resistors to ground to form the first high pass filter. The second is between pins one and two, this dampens higher (noise) frequencies before the gain stage. If you want to make the circuit more sensitive and jumpy put a higher resistor between pins one and two. Next stage is taking the signal through a 10k pot to the input of the second op amp. this allows you to control the overall gain of the circuit( i like a bigger pot here for more resolution). it then goes in a second filter circuit which hopefully takes out the rest of the noise it is set higher than the first because of the second stage amplification. the signal out to the micro-controller comes from pin 7. the pot on pins 3 and 5 allow you to float the voltage to whatever you need especially handy if your amplifying a ac signal.

pictures of finished board

Below is the code i used to input from the Arduino micro-controller :

heart detection code

Here is the small display app i wrote in java using processing's serial library:

graphing code

OPerational AMPlifiers:

Here are two circuits designed around the lm358n op amp. For a quick tutorial visit here.The heart of the op amp is a comparator circuit, the circuit takes two positive voltages into an inverted and non-inverted input then compares them. If the non-inverted voltage is higher then it saturates to a positive voltage if the inverted is larger then it saturates negative or “low”. The key to the amplifier circuit is a feedback resistor between the output of the circuit and the inverted input. This sends back a “dampening” voltage to the input not allowing it to fully saturate and controls the output voltage.

 

 

 

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