Diodes!!

I think diodes are really neat! They let current through one way, but not the other.  Basically a one way gate. Ideally, the diode would start to transmit as soon as the voltage is positive, but in real life, they have a small lag, ~0.6V for regular, 2.2 for red LEDs.  They can also be thought of as resistors, which are either infinity resistant (at negative V) or basically 0 at positive V.
  . I tried Measuring the resistance of a 1N914 diode, and got 5.30Mohm one direction and an error the other direction, as in too large to measure.

Other Neat things that you can do with Diodes are fiddling with sine waves!

Lab 3-2, we made "Half Wave Rectifiers", which basically blocked the negative side of a sine wave, from an wall-outlet. Apparently some cheapo companies will consider this DC, since it never goes negative.  The Blue is the full sine wave and Yellow is the rectifier.. As you can see, there is a little discrepancy from the height of the blue and yellow, that's because of the unideal nature of the diode, if you look closely, the yellow is 0.6V bellow the blue.  Pretty Neat huh?

We basically just kept adding elements to the original circuit to make new and exciting things.  If you add a Capacitor, then the signal starts to look like a pretty flat line! Getting pretty close to DC!

This Cap is 47uF, coupled with the 2.2k resistor, which is Red Red Red :)

give you an RC value of 0.1, which is much greater than 1/60 seconds so the Cap doesn't discharge much between peaks at 60Hz, which makes little ripples in the signal.  We can calculate the ripple amplitude using :

 So ripple amp = 0.16*Vmax. Vmax = ~10V (see the graph?)
dV = 1.6Volts.  If you look in the graph (the big boxes are 5V) you can see the ripple dip by 1.3 or so, which is pretty close, given the printed values on electronics can vary by 20%


Lab 3-5: Signal Diode / Rectified differentiator.

This one is like the differnetiator plus a capacitor.  If you look, you can kind of see that the yellow looks like a derivative of the blue line, if you only plotted the areas of positive slope.  The second picture is the same circuit without a 2.2k resistor load at the end, which basically altered the RC so now you can see the discharge signal amplified.

Lab 3-6: Diode Clamp


This circuit can be used to 'clamp' the voltage.  Basically trim the max output: I calculated the dynamic resistance of the diode, without the voltage divider, and got 250 Ohms.  With the full circuit set up, the capacitor is acting with a very low resistance at the sine frequency, thus making the voltage low and clamping the output.

Lab 3-7: Diode Limiter
You can use two diodes in opposite directions to let through and still limit both sides of the signal! This would be very useful for sensitive electronics that would be fried by high voltage!