EE 330 Lab 2 – Simple DC Currents with Resistors and Resistive Sensors
Joe O’Connor | Onochie Ani
Lab Preformed 2/6/15
The objective in experiment two is to become familiar with resistors and how to measure them
when they are both in series and parallel in the circuit. We also learned how to use photo resistors,
thermistor, potentiometer, and other tools such as the tool to measure light.
Before this lab, my partner and I read the experiment 2 section in the book. This helped us
understand what was going to take place and what we could expect in the experiment. We also
reviewed the properties of resistors and relevant equations when placed in series and parallel. We also
reminded ourselves of other equations like Ohms law, VDR and Kirchoffs laws.
Step one asked us to choose resistors for X that were either 1k ohm, 2.2k ohm, or 3.3k ohm and
for Y to choose a resistor double of X’s Value. We chose 2.2k ohm for X and 4.7k ohm from Y (we
couldn’t find a 4.4k ohm resistor. Then to set the power supply to 10v. We were asked to connect the
resistors in series to match this picture:
We needed to calculate the V1 and V2 on paper using kirchoffs laws before measuring any values using
the DMM.
When Vs = 10
V1 = 3.18
V2 = 6.812
Using the DMM our values were.
X = 2.17
Y = 4.65
Vs = 9.987
V1 = 3.187V
V2 = 6.819V
The values were pretty similar from the nominal vs the measured value.
V2 % difference = 3.187-3,18/3.18 * 100%
=.2%
V1 % difference = 6.812-6.819/6.812 * 100%
= .1%
Step 2 was very similar to step 1but instead of series we put it in parallel like in the picture
below. We also needed to find current instead of voltages.
From the picture, i1 goes with X an i2 goes with Y. I1 plus i2 should equal i3. To calculate the values of
the currents on paper we use ohms law.
I1 = v/rx
= 10/2.2
= 4.54545mA
I2 = v/ry
= 10/4.4
= 2.272727mA
To get i3, we used properties resistors in parallel to find the equivalent resistance. We got 1.498 k ohms.
Next we had to apply ohms law.
I3 = 10/1.498
= 6.675567 mA
Using the DMM our values were
I1 = 4.598mA
I2 = 2.1514mA
I3 = 6.7243mA
We concluded that the calculated and measured values were very similar. The percent differences were:
1.1%, 5%, .8%. KCL is satisfied.
Step 3 involved hooking up a resistor (either 1.1 2.2 or 3.3k ohm resistor) to the power supply in
increments of 0.2 from -1V to 1V. Our goal is to measure both voltage and current across the resistor
using 2 DMMS (one for current and one for voltage). We then set the power supply to -1 then measured
the current and voltage values. We then needed to repeat this step at
-0.8V, -0.6V, -0.4V, -0.2V, 0V, 0.2V, 0.4V, 0.6V, 0.8V, 1.0V
Our values were:
PS
-1.0
-0.8
-0.6
-0.4
-0.2
0
0.2
0.4
0.6
0.8
1.0
Voltage
-1.0025
-0.8057
-0.6068
-0.4067
-0.2056
-0.00376
0.2062
0.40687
0.60718
0.80587
1.00299
Current
-0.000465
-0.000369
-0.000278
-0.000189
-0.000099
0.000004
0.000102
0.000185
0.000283
0.000368
0.000465
0.0006
0.0004
0.0002
0
-1.5
-1
-0.5
-0.0002
-0.0004
-0.0006
Series1
0
0.5
1
1.5
From this graph above, we concluded that voltage has a direct linear relationship with the current. As
current rises so does voltage. Using excel we got the slope to equal 0.00042. The slope would rise more
slowly the larger the resister gets.
Steps 4 and 5 required us to measure actual value of Y (the resistor) used in the previous step.
Then to compare the measured value vs the nominal value by the color code. We grabbed a 2.2k ohm
resistor. The resistor color bands was red, red, red, gold; this should equal 2.2 ohm. According to the
chart on appendix A, the first and second digit was 2. The third digit is also a 2 which acts as a multiplier
of 10. The last gold band is the tolerance band which was 0.5%. Using all this information the values
indeed add up to 2.2k ohms. Using the DMM we got the resistance to be 2.15k ohm which is a 2.2%
difference.
Step 6 asked us to use a photo resistor and to measure the resistances of the photoresistor
under 4 different light levels; dark, med-dark, med-light and max light. To accomplish this we used a tool
that measured light in FC (I forget the name of it), the DMM and a photo resistor. We hooked up the
photoresistor to the DMM and placed the tool that measured light right next to the photoresistor. We
then covered up the photoresistor with our hands and recorded both the light level, and the resistance
level. We did this for 4 different light levels. Our values are in the chart below.
Light Level (f-c)
Dark
MedDark
MedLight
Max
Light
Y Resistance (ohm)
1
2100
10
827
37
515
357
156.4
2500
Resistance
2000
1500
1000
Series1
500
0
0
100
200
300
400
Light Level
We concluded that the darker it is, the higher the resistance. The plot is linear other than the extreme
outlier of complete darkness. Using the change in ohms divided by the change in light, we
approximated the photoresistors light sensitivity to be around 141.44.
Step 7 was similar to the previous step but instead of a photoresistor we used a thermistor. This
changes in respect to temperature rather than light. We hooked up the thermistor just like the
photoresistor but instead of changing the light level we were asked to change the temperature level and
instead of putting the light sensing tool next to the resistor we placed a temperature meter next to the
resistor. To do this step we were supposed to use a heat gun but we did not have one. This made this
step very hard because we could not change the temperature very easily. We tried our best to increase
the temperature by breathing on it but it only slightly increased the temperature. Our values are in the
chart below.
Temp in C
Resistance
25.6
9.626
27.6
8.6
29
7.8
12
Resistance
10
8
6
Series1
4
2
0
25
26
27
28
29
30
Temp in C
From the chart and graph above, we concluded that the higher the temperature, the lower the
resistance. From the data we calculated the thermistors temperature coefficient to equal something
around 0.5.
For steps 8 and 9 we were asked to choose 2 different resistors, X and Y. We used the same
ones we have been using, X = 2.2 and Y = 4.7. We were asked to measure them alone and the measure
them after we hook them up in series and parallel. The calculated value for series is 2.2 + 4.7 which is
6.9k ohm. Parallel is 1/(1/2.2 + 1/4.7) which equals 1.49855k ohms. Next we hooked up the resistors in
series and measured the value using the DMM. We got 6.873 k ohm from resistors in series using the
DMM. Then we hooked up the resistors in parallel and measured the value, we got 1.446k ohms. The
percent difference in series is 1% and the percent difference in parallel is 3.5%.
(skip step 10)
For step 11, we were asked to set the power supply to 10V. Then we had to choose 2 resistors
between 2 and 10 k ohms that don’t equal each other. We used the same 2.2 and 4.7k ohm resistors.
We put the resistors in series and then set the power supply to 10V. The measured values for r1 = 2.18
and for r2 = 4.562. The voltage at r2 = 6.7909. Equation 4: Vs * R2/(R1+R2) = v. We got v to equal 5.981.
This satisfies equation 4 because the values were pretty close.
Step 12 asked us to design a voltage divider that yields V = 1/3 Vs with Vs = 10V. We needed to
have the voltage of R2 to be 1/3 of Vs (10V) which is 3.33V. We used the same 2.2 and 4.7k ohm
resistors. V = 1/3(10) * R2/(2.2+R2) = 1/3. This made R2 have to be 1.1k ohms. We chose the 1.1k ohm
resistor and connected both in series. We then used the DMM to measure the voltage at R2 which was
3.3225V. This is very similar to the 3.33V that was needed so equation 4 was satisfied.
For steps 13 and 14, we were asked to use the potentiometer. We had to measure the
potentiometer when it was isolated, we had to measure the min and max resistance of the
potentiometer connecting wires from nodes D and F. We measured the min resistance to be around 9k
ohms and the max to be about 9.5k ohms. With everything hooked up we were then asked to turn the
knob on the potentiometer to 100%, 75%, 50%, 25%, and then 0%. Using the DMM we measured the
voltage of the potentiometer after turning it to specified values.
100% = 10v 75% = 2.5v 50% = 5v 25% = 7.5v 0 = 9.5v
12
10
8
6
Series1
4
2
0
0
20
40
60
80
100
120
Step 15, the last step, asked us to design a light sensing voltage divider such that v = 5v in room
light and <2v=V in max darkness. This requires use of the photoresistor. We measured the photoresistor
at room lighting and we got 800 ohms. We then plugged that into equation 4 to make
5v = 10 * R2/(800 + R2).
This equation says that R2 has to equal 800 to get the intended 5V output. We then measured
resistances of the photoresistor in 3 different levels. The graph that was produced in linear.
Light Level
Dark
Med
Light
FC
1
30
100
V Output
1.6
5
9.8
12
10
8
6
Series1
4
2
0
0
20
40
60
80
100
120
Conclusion: This second experiment got us familiar with simple
resistive circuits and got us to understand how to take certain
measurements. We got familiar with photoreistors, thermistors,
and potentiometer. We also had to use fundamental laws of
circuits such as Kirchoffs and Ohms law.