Electronics Lab - Day 5

Lab 2-6 : Garbage Detector

We created a high pass filter in order to see the "garbage" on the regular 110v power lines. We used a transformer to reduce the voltage to a safe level and introduced that as the input voltage of the high pass filter. The input voltage looked like a clean classical sine wave but the output of the filter looked like this:

Which is all of the high frequency garbage that is sitting on top of the power line.

Lab 2-8 : Blocking Capacitor

In this section, we were trying to figure out how to add an offset to a time dependent frequency(sine wave). In order to do this, we obviously need a function generator to give us the sine wave and also a DC power source to provide the offset. However, if we connect these two power sources, they are going to "compete" for dominance of the circuit and in this case, the AC power source will "win". Therefore, we add in a blocking capacitor in this diagram:

This configuration allows the AC voltage to ride on top of the DC voltage so that we have correct output function with a DC offset.

Resistance of a Diode

We connected a 1N914 diode to an ohmmeter to measure the resistance as a function of current. As we changed the scale on it, the ohmmeter changes the amount of current that it is putting out. Smaller scales of the meter use larger currents and we found that the decreased at smaller scales. This makes sense because a diode tries to stay at a constant voltage, V=IR, so when we increase the current the resistance must drop in order to keep a constant voltage.

Lab 3-2 : Half Wave Rectifier

The question that we were trying to answer in this section was: How do we change an AC current source into a DC current source? First we built this circuit.

This circuit only allows through the positive current. This is because, in practice, diodes only let through current in one direction. When the input voltage is much lower than 0.6v, the diode has a very high resistance because it's still trying to maintain a 0.6 v drop. On the other hand when the input voltage is much higher than 0.6v, the diode has a very small resistance and therefore the voltage at output will be almost the input voltage minus the 0.6 v drop across the diode. This can be seen clearly in our resulting output voltage.

Ripple

Now we added a capacitor in parallel with the resistor. This adds an RC time lag to the circuit as the capacitor discharges meaning that the capacitor is not going to fully discharge in the time that the voltage drops below the maximum voltage. We calculated what the voltage drop would be using:

R = 2.2kohms

C = 10 uF

Vmax = 11v

and we found that the change in V = 5.8v. Which matches with our experimental results below where we estimated the change in voltage to be 5v.

Lab 3-5 : Signal Diode

We created the circuit below, which has all the components of a differentiator and a half wave rectifier.

We found that this circuit does in fact just combine the effects of a differentiator and a half wave rectifier. When we put in a square wave, the result was upward spikes of voltage where dVin/dt was positive and there were no corresponding spikes when dVin/dt were negative.

Lab 3-7 : Diode Limiter

This type of circuit limits the maximum output voltage to 0.6 volts. Because diodes only let current through in one direction, we also need to add another in the other direction, parallel to the first diode. In this way, both the positive and negative voltages are replicated with a maximum of 0.6 v and a minimum of -0.6 v.