D3 - Dusk-to-Dawn Light

We started our day with a pictures of wiener dogs and a bun with a wiener doing inside. Our thought exercise of the day in terms of Engr44 was what would happen to a hot dog if it was applied 120 Volts from an outlet. We wrote our prediction in terms of I vs T and in words in the white board below.

Graph of what we think would happen in I vs T and we choose it would burn out quickly. We were wrong, the hot dog took a long time to even began to fizzle and smoke.

We then moved onto another question where Prof. Mason decided it was a good idea to attach LED to the wiener dog and see if the LED would light and if so how bright.

Here is the picture of Prof. Mason brilliant wiener experiment.

White board work explaining  what we thought would happen.

We said that the LEDS parallel would light up. Those in series would not.

Another picture better explaining why parallel works and series doesn't longer R higher potential difference.

We then moved onto finding Dependent Source Examples.

Picture of the first one, 2 loops, one ideal and one dependent source. Used KCL at node.

White board work of the second, used loops and KCL at nodes.

We then moved onto the Voltage Divider. But spent some time on resistors in series for Req and resistors in parallel for Req. Which would be useful later on for using a voltage divider.

White board work for finding Vout.

White board work for values given in class for the voltage divider example. We used the formula earlier derived to get these values of R1 and R2.

Prof. Mason then told us in the real world resistor come in set values and then raise in cost by alot the more special the resistance is. Thus we found the cheap set values of resistors and got the same function out of voltage divider by using the voltage divider equation.

We then checked our resistors numbers into an example of finding if our numbers would provide enough wattage and current needed of a circuit.

Another example of resistors and how they would work in a problem with resistors in series and in parallel circuit.

After all the dirty white board work we moved onto the lab of the day which would use everything we learned thus far.
Dusk-to-Dawn Light:
The pre-lab was to draw the circuit and use KVL.

White board work for prelab and other stuff, we used KVL on the outer loop and found Rp.(Resistance of photocell), other pictures has Vb of the photocell.

Picture of proof of the BJT and LED working.

Picture of our circuit connected together on breadboard.

The video below plays showing the LED turning brighter and off with relationship to the hat covering up the light hitting the photocell.

Final picture of the voltage recorded of the photocell at .1V at 5k ohms and 1.4V at 20k ohms.

We finish up talking up how potentionmeters and DC meters work, just like a voltage divider. Similarly with current. The end of class had a link to EEblog which was very useful in understanding more how DMM read voltage, current and resistance of an element.

In summary:
We learned that wiener dog takes a log time to warm up even when it connected straight into a plug. The LED in series were shorted out and produced no light while the LED in parallel were bright. We talked about dependent sources and how useful KCL is when used properly at nodes. How resistors work in series, just add them; in parallel, R1R2/(R1+R2), resistors in parallel will never be higher than the smallest one. Voltage dividers follow the formula V1 = (R1/(R1+R2)V). In Dusk til dawn lab learned how to do prelab work and apply it usefully to actual circuit. BJT have a base, emitter, and collector, (CBE top to bottom) and LED's are polarized, which means the orientation is important and photocells are pretty fun things to work with in electronics.