Laboratory 6 Daniel Choi 904169062 Lab 2a 8 6 Phototransistor a b After building the circuit below we saw that the average input photocurrent was 0 0011 mA Across the summing junction the current was 0 0003 or nearly c We put the phototransistor at the end of a cable and connect it to our circuit We check the output after the op amp figure 1 the summing junction when the phototransistor is covered figure 2 and the summing junction when the phototransistor is uncovered figure 3 We put our scope to autotrigger and we set it to 250msec div When we unplug the feedback resistor we see that the circuit stops working We then have the photoresistor look at itself on the scope The photoresistor seems to go a bit crazy Figure 4 8 8 Push pull buffer b We build the following circuit We see a lot of noise so we add electrolytic capacitors to clean up our signal on the scope We see the classical crossover distortion when we plug our scope at point a in the circuit above Figure 5 We connect a speaker to hear the waveform and we hear a buzzy noise When we reconnect the right side the feedback resistor to the push pull output put our scope to point b our crossover distortion disappears Figure 6 The output of our op amp looks like figure 7 We then use the speaker to listen to the waveform and we heard a smoother sound When the feedback resistor is unplugged we hear a fuzzy sound from the distortion because of the fourier There are many frequencies trying to make the sine wave and those frequencies make it buzzy 9 2 Integrator d We construct the active integrator below We drive it with a 1kHz square wave with amplitude of 2V We find the pk pk voltage was 2 20V The expected output of the square wave was a triangle wave figure 8 The function of the 10M resistor is to take away the DC offset If it were not included in our circuit it would cause the DC offset to increase When we removed it from our circuit we saw exactly this and there was a drift in the DC offset 9 3 Differentiator e We build the following circuit We then drive it with a 1kHz triangle wave The expected output of the triangle wave was a square wave as we see in figure 8 However we see a slight slope on the differentiated waveform because there is a slight offlinearity from the function generator 9 4 AC amplifier microphone amplifier f We build the circuit below We then watch the oscilloscope as we make tones with our mouth into the microphone We set our divisions to 500msec div As shown in the figure above we see that whenever we make a sound there is a bunch of waves that show up on the scope The waves are visual voice recordings We then change our divisions to 500 sec div and we try to change the frequency We see that when we whistle a higher tuner the amplitude increases Wien Bridge h We build the circuit as the following The Wien Bridge gave us a nice sine wave that had a frequency of about 1 6kHz When we removed the small amount of negative feedback the Wien Bridge failed to work properly We then took out the lamp and put an equivalent resistor of about 20 We saw that the circuit did not work This worked properly for the lamp because as there was more current going in through the lamp the resistance of it changed as well as the lamp dissipating more heat The invariant resistance of the resistor is the reason why the circuit did not work with the equivalent resistor