Day 6 March 11, 2009

The first thing we did in the class was a quiz. The quiz is about using the Kirchhoff's Rules to find current in the circuit. Then using the current to find the voltage and the power to compute the total power.

Generally, we use the sum of current and voltage in a loop are both equal to zero to find the current. First, The junction rule I1=I2+I3 will setup the first formula, and the loop rule will create the other two formulas. Then, we can do some algebra for the unknowns in the formulas to find the current. After that, V = IR can be used to find the voltage by current and resistant. Finally, use P = IV to get the power of each resistor, and add them up to get the total power.

I did the questions wrongly, but I found my mistakes soon. All loops have to in the SAME direction. It was a good quiz because I even did not find I was doing something wrong in the homework!


The second part in class was slightly different with the class. We were learning something which is not in the book! The robot project was started! Before touching the hardware, we had to learn some theory for that.

What we learned in this part was the protocol for the devices to communicate. We learn how it works. It translate ASCII code(American Standard Code for Information Interchange), which is commonly used in computer system to represent characters and to some digital signals. The character in ASCII code first translates to 0 and 1, then it reverses the order of the code then translates to positive voltage for 1 and positive voltage for 0.


The third part was doing some labs. We use a voltage divider, a potentiometer to build a bridge circuit to measure the temperature. We take the voltage in the freezing and melting point, which are already known as 100 and 0 degree Celsius, to calculate the room and the body temperature. From the result, we will get a line which show that they are in linear function.

An interesting thing in the lab is that we found this device is really sensitive. It could even catch the temperature change caused by our human body moved away for a few centimeters!