Photoresistors!! 5-11-09

Hey Guys-

On Monday we learned about photoresistors and had a robot day! Photoresistors are light sensitive resistors whose resistance decreases with the amount of light falling on them.

We will be using photoresistors on our robots for the "Follow the line" competition and for "Robot Sumo."

We've all seen photoresisitors somewhere in our lives.....for instance my car as an auto setting for my headlights to turn on and off. When the resistor has enough light falling onto it, it causes electrons to jump into the next conduction band. The resulting free electron conduct electriciy, and therefore low the resistance of the resistor.

To use this on our robots, we needed to figure out the resistance range of the resistor for different light intensities. We used the 'white' of the our white boards and the black of non reflective electrical tape.

Once this is figured out, interface the resistors using voltage dividers to your microprocessor. The photoresistors will control one or both of your motors. You'll want to think about how you want your robotto behave for the line following competition and also think about what you want your robot to do when it faces the white outline of the sumo ring.

Oh...Mason also did some cool stuff in class...no he didn't light either of the Peter's on fire, but he put stuff in a microwave that shouldn't have gone into it, and made sparks fly.

LRC Circuits - 5/6/09

Today in class we had lots of fun with oscilloscopes and LRC circuits. If you haven't looked at Mason's AC circuits notes, I highly suggest you do or you might internally combust due to massive confusion. Mason's notes really helped me understand the vector problems in the HW.

We took a good look at phase angles and how to caluclate them and what they mean. Basically when looking at both current and voltage in an oscilloscope, current and voltage will both oscillate sinusoidally but not at the same time. The difference in which the current leads or lags the voltage is called the phase angle.

Phase angle (phi) = tan(-1)(XL-XC)/R = 2pi*delta t/T(dr)

Where T(dr) = the period of oscillcation of the driving emf.

Since it has been almost 10 years since I had to figure out the period of a function, I spent the entire class asking myself WTF? So it also might be really useful to know how to find the period;

Period(T) = 1/f
w=2*pi*f

We briefly went over the Root Mean Square Current and Voltage. Mason proved that the average current and voltage on always equal to zero, but the average power of the AC circuit is not equal to zero....ya we've all been zapped by AC circuit.

In general, your equations of Voltage and Current will look something like this for a LRC AC circuit in series;

If circuit is voltage diriven;

V(f)= Vmax*sin(wt)
I(f)= Imax*sin(wt-phi)
phi = phase angle

If circuit is current driven.

I(f)= Imax*sin(wt)
V(f)= Vmax*sin(wt-phi)

The circuit will still obey Kirchoff's rules.

Good luck on all of the H-dub!!

AC Circuits Notes

The notes are available here:
http://docs.google.com/Doc?id=d3w6sww_1142spch8thj

STRIKE #3

Speaking of Monday, Mason wasn't here on Monday, but Peter, Me, Brandon, Chris Z., and quite a few others were there doing a little work on our robots. Well, Peter wasn't working on any robots, but he did do his SI session. :3

We took our tests last Monday, right? So... extra credit? XD