Capacitors

Today i did 4 different capacitor tests. First i hadto wire up a simple circuit containing a capacitor and a resistor, which would be easy enough to switch capacitors/resistors when i needed to change the test situation. Once this was done i connected it to the oscilliscope and set the oscilliscope for the specific capacitor.

The above picture shows the curve of a capacitor charging. The horizontal axis shows time, each block denotes 10ms. The vertical axis shows voltage, and is pictures in blocks of 5 volts. So, by looking at it, it takes aproximately 50mS to charge up to 12v.
What is interested is that, in the first 10mS, the capacitor is over halfway charged, yet it takes another 40mS to completely charge it.
This is why the equation  RxCx5=T to find the charge time of a capacitor. In this particular image, the calculation was 100(-6)x100x5=50mS. This calculation shows correct with the image on the oscilliscope, and shows that i have used the correct components and they are within their spec.
I then carried out the same test again three more times with different capacitors and resistors.
I found from doing these different tests, that changing the capacitor or the resistor may change the length of time that it takes for the capacitor to charge, but the curve will stay the same. This shows that the nature of charging a capacitor is a constant.

Diodes

 Today we worked on diodes. At first we looked at voltage drops across diodes and LEDs with our multimeters. We also looked at identifying the Anode/Cathode without using a multimeter. On a diode, there is a silver stripe on the cathode end, and on a LED there is a flat edge.

Today we started to use bread board for component analysis. First up we measured and calculated current and voltage across a diode in a circuit. I wired up a simple circuit containing a 1K resistor, a 1N4007 Diode, and a 5v power supply. I then calculated what current should be running through the circuit using the formula I=(Vs-Vd)/R. (5v-.7v)/1000ohms means that the current should be approx. 4.3mA with a steady supply voltage. My measurement with the multimeter showed 4.4mA which was expected as my supply voltage was slightly higher than 5v. Next we calculated voltage drop. From prior advice from my tutor, i knew that the voltage drop across the diode should be .6-.7v approx. over each diode. My multimeter proved my teacher correct, as the voltage needed to work it was indeed .64v.

I then replaced the diode with a LED and did the same tests. The voltage drop was significantly higher(1.8v), i believe this was because it is a bulb aswell as a diode. I calculated that the current should be similiar to 3.8mA. It was 3.2mA.

My next experiment on diodes was on a Zener diode. I created a compound circuit with a resistor and a Zener Diode in parallel, and a resistor in series. Then i calculated the value of Vz (Voltage drop across the Zener). Vz=4.97v when Vs=10v, and 5.1v when Vs=15v. This shows that if the voltage increases, the Zener Diode will stabilize it by raising its voltage drop. This is why a Zener diode is helpful as a voltage stabilizer in a circuit.

My final experiment involved putting diodes ( A Zener in reverse bias, and Rectifying in forward bias) in series with a resistor. I ran ten volts through the circuit, and my results were: Vz=4.6v, Vd=.6v, Vr=4.7v. I then adjusted Vs to 15v, and re-measures my voltage drops. I got Vz=4.8v, Vd=.7v, Vr=9.5v. This shows that once the diodes have reach their breakthrough voltage, they do not require any more voltage to operate, thus the resistor will consume what voltage is left.

09/03/11 Resistor recognition

Here is the picture we worked from today. It was a great image as it not only showed us what each resistor means, but it also was easy to learn from and remember. Another great study technique was the quote 'Bad Beer Rots Our Young Guts But Vodka Goes Without'. This quote shows all of the colours, from black to white, in their order, from 0 to 9 respectively.
With these aids, we worked out the resistance of six different resistors by looking at them only, then double checked the values with our multimeter.
The first resistor i calculated had brown, black, drown and gold bands respectively. As i had previously read about resistor recognition, i knew the first two bands (Brown and black) were the main numbers to be calculated. The third band (Brown) has a value of one, which means it adds one zero to the end of the value. The gold band at the end denotes that the resistor has a variation specification of 5%. I concluded that the resistor should have a value of 100ohms, and with a 10% variation, will be between 90ohms and 110ohms.
The second resistor had red, red, yellow, and gold bands. My calculations told me that the resistance should be between 209k and 231k. My multimeter showed 212k, which is within the spec of the diode.
My third diode had brown, black, orange, and gold bands. I calculated that, to be within spec, it should have a resistance of 9.5k and 10.5k. My multimeter read 9.98, which is near perfect in terms of being in spec.
The fourth diode had brown, black, green, and gold bands, which shows that it should have between 950k, and 1.05M. The multimeter reading was .993M, which is within spec.

One thing i found was that with some resistors, there is confusion as to which way it should be read. With this problem i found that reading it first with the multimeter, and then confirming with a visual check was quite effective.
After more practice I feel I will become confident in resistor recognition, and will be able to find values with ease.