Lab 6

Operational Amplifiers

Explanations of the pin numbers below:

1: DO NOT USE	8: DO NOT USE
2: Negative input	7: +10V
3: Positive input	6: output
4: -10 V	5: DO NOT USE

1.  You will use the OPAMP in “open-loop” configuration in this part, where input signals will be applied directly to the pins 2 and 3.

a.       Apply 0 V to the inverting input. Sweep the non-inverting input (V_in) from -10 V to 10 V with 1 V steps. Take more steps around 0 V (both positive and negative). Create a table for V_in and V_out. Plot the data (V_out vs Vi_n). Discuss your results. What would be the ideal plot?

Below is a plot of our measured data.

Vin (V)	Vout (V)
-5.03	4.49
-4.05	4.49
-3.04	4.49
-2.01	4.49
-1.05	4.49
-0.25	4.49
-0.098	4.49
0	4.49
0.097	-3.74
0.257	-3.74
1.05	-3.74
2.06	-3.74
3.05	-3.74
4.03	-3.74
5.01	-3.74

A plot of our Vin vs Vout data.  Vin is the X-Axis and Vout is the Y-Axis.

For every negative we measured either -3.74 V or -3.73 V as the output regardless of the input, and for every positive voltage we measured 4.49 V for the output.  Since the change from positive to negative is nearly instantaneous it makes sense that we were unable to measure the instant it changed with the equipment we have.  Even at 0 V, with the input connected to ground and with the input not grounded we still measured 4.49 V as the output.

b.  Apply 0 V to the non-inverting input. Sweep the inverting input (V_in) from -10 V to 10 V with 1 V steps. Take more steps around 0 V (both positive and negative). Create a table for V_in and V_out. Plot the data (V_out vs Vi_n). Discuss your results. What would be the ideal plot?

Below is a plot of our measured values.

Vin (V)	Vout (V)
-5	-3.74
-4.04	-3.74
-3.02	-3.74
-2.01	-3.73
-1.03	-3.73
-0.764	-3.73
-0.531	-3.73
-0.25	-3.73
-0.104	-3.73
-0.097	-3.73
0	4.49
0.097	4.49
0.594	4.49
1.04	4.49
2.06	4.49
3.07	4.49
4.04	4.49
5.04	4.49

A plot of our Vin versus Vout data.  Vin is the X-Axis and Vout is the Y-Axis

For every negative value of input, we measured 4.49V as the output, even at 0 V (with the input connected to ground and with the input ungrounded) we got 4.49 V as the output.  For every positive value of input we measured -3.74 V as the output.  Again this makes sense because the moment of change is nearly instantaneous we can't measure it with out equipment. 

2.  Create a non-inverting amplifier. (R₂ = 2 kΩ, R₁ = 1 kΩ). Sweep V_in from -10 V to 10 V with 1 V steps. Create a table for V_in and V_out. Plot the measured and calculated data together.

Vin (V)	Vout (V)
-5.01	-3.63
-4.03	-3.63
-3.02	-3.63
-2.02	-3.63
-1.02	-3.03
-0.74	-2.21
-0.47	-1.38
-0.098	-0.292
0	0.0001
0.098	0.294
0.36	1.05
0.77	2.3
1.03	3.05
2.1	4.25
3.09	4.25
4.12	4.25
5.07	4.25

This is a chart showing our measured values

Vin	Vout
-5.01	-5
-4.03	-5
-3.02	-5
-2.02	-5
-1.02	-3.06
-0.74	-2.22
-0.47	-1.41
-0.098	-0.294
0	0
0.098	0.294
0.36	1.08
0.77	2.31
1.03	3.09
2.1	5
3.09	5
4.12	5
5.07	5

This is a chart showing our calculated values

This is a graph showing our measured (blue) vs calculated (orange) values.  Vin is the X-Axis and Vout is the Y-Axis

3.    Create an inverting amplifier. (R_f = 2 kΩ, R_in = 1 kΩ). Sweep V_in from -10 V to 10 V with 1 V steps. Create a table for V_in and V_out. Plot the measured and calculated data together.

Vin (V)	Vout (V)
-5.03	4.18
-4.07	4.19
-3.04	4.2
-2.05	4.1
-1.05	2.09
-0.63	1.25
-0.22	0.42
-0.098	0.197
0	0.0001
0.098	-0.194
0.252	-0.5
0.763	-1.51
1.07	-2.13
2.01	-3.58
3.03	-3.56
4.04	-3.54
5.02	-3.52

A chart showing our measured values

Vin	Vout
-5.03	5
-4.07	5
-3.04	5
-2.05	4.1
-1.05	2.1
-0.63	1.26
-0.22	0.44
-0.098	0.196
0	0
0.098	-0.196
0.252	-0.504
0.763	-1.526
1.07	-2.14
2.01	-4.02
3.03	-5
4.04	-5
5.02	-5

A chart showing our calculated values

A graph showing our measured (blue) versus our calculated (orange) values.  Vin is the X-Axis and Vout is the Y-Axis.

4.    Explain how an OPAMP works. How come is the gain of the OPAMP in the open loop configuration too high but inverting/non-inverting amplifier configurations provide such a small gain?

An OPAMP amplifies an input signal based on whether it is inverting or non-inverting.  An OPAMP cannot take an output voltage higher than the voltages of the V- and V+ DC power supply voltages.  If it is an inverting amplifier it will take the polarity of the input and reverse it, while a non-inverting amp will have input and output polarities that match. 

Open loop amplifiers do not have the resistors to limit the gain, so the gain is much higher in open loop configurations.  In an inverting amplifier the gain is equal to - Rf / Rin and in a non inverting amplifier the gain is equal to 1 + R2 / R1.  As you can see in parts two and three, with these resistors connected to the amplifiers it is much easier to visualize the slope from -5V to +5V. 

Temperature Controlled LED System

TMP36 Temperature Sensor: Pin layout – look up characteristics to calculate temperature from datasheet (under Bb/Week6).

Temperature Sensor: Put TMP36 temp sensor on breadboard.

·       Connect the +V_S to 5 volts and GND to ground.

·       Using a voltage meter, measure the output voltage from the V_OUT. Now put your finger (or cover the sensor with your palm) on the TMP36 temperature sensor for a while, observing how the output voltage changes. Check Fig. 6 in the data sheet (EXPLAIN).

Essentially the temperature acts as a variable to how much resistance the temperature sensor experiences between the input voltage and the output voltage.  So at room temperature we measured around .74V output, and the highest voltage we could reach with the hair dryer running was .95V.

Relay (Manual under Bb/Week6)

Pin 1 – Input voltage (amount of voltage sent to pins 3 or 4)

Pin 2 – Power supply

Pin 3 – V_out = V_in when V_in > V_threshold

Pin 4 – V_out = V_in when V_in < V_threshold

Pin 5 - GND

schematic view is the bottom view!

1.       Connect your DC power supply to pin 2 and ground pin 5. Set your power supply to 0V. Switch your multimeter to measure the resistance mode; use your multimeter to measure the resistance between pin 4 and pin 1. Do the same measurement between pin 3 and pin 1. Explain your findings (EXPLAIN).

Our measured resistance between pin 1 and pin 4 is very small, measuring at only .124 Ohms.  Our measured resistance between ping 3 and pin 1 is .OL, or overload.  Too much resistance for the DMM to measure. 

The resistance between pin 1 and pin 4 gives us a small value because pin one is the input voltage and pin 4 is the output voltage when the input voltage is less than the threshold voltage.  The resistance between pin 1 and pin 3 is so high because pin 3 is the output when the voltage in is greater than the threshold, and the voltage in is 0 V which gives us a very high resistance for pin 1 to 3.

2.       Now sweep your DC power supply from 0V to 8V and back to 0V. What do you observe at the multimeter (resistance measurements similar to #1)? Did you hear a clicking sound? How many times? What is the “threshold voltage values” that cause the “switching?” (EXPLAIN with a VIDEO).

Vin (V)	Resistance (Ω) Pin 1-4	Resistance (Ω) Pin 1-3
0	0.124	.OL
1.08	0.22	.OL
2.05	0.218	.OL
3	0.218	.OL
4.02	0.218	.OL
5.12	0.231	.OL
5.23	.OL	0.194
6.18	.OL	0.189
7.14	.OL	0.186
8.04	.OL	0.185
7.12	.OL	0.23
6.08	.OL	0.23
5.33	.OL	0.23
4.01	.OL	0.23
3.1	.OL	0.23
2.22	0.23	.OL
1.17	0.229	.OL
0	0.227	.OL

We hit the threshold at 5.23V, after that we continued to 8V and didn't hear another click.  On the way back down to 0V we heard a click at 2.22V.  The red rows signify when the switch happened.

A video showing the resistance before the first switch

A video showing the resistance after the first switch

3.       How does the relay work? Apply a separate DC voltage of 5 V to pin 1. Check the voltage value of pin 3 and pin 4 (each with respect to ground) while switching the relay (EXPLAIN with a VIDEO).

A video showing the switching of the relay with multi-meters hooked up to each output.

LED + Relay

1.       Connect positive end of the LED diode to the pin 3 of the relay and negative end to a 100 ohm resistor. Ground the other end of the resistor. Negative end of the diode will be the shorter wire.

2.       Apply 3 V to pin 1

3.       Turn LED on/off by switching the relay. Explain your results in the video. Draw the circuit schematic (VIDEO)

A video showing the switching of the relay with LED's

A drawing if our switch circuit.

Operational Amplifier (data sheet under Bb/week 6)

1.       Connect the power supplies to the op-amp (+10V and -10V). Show the operation of LM 124 operational amplifier in DC mode with a non-inverting amplifier configuration. Choose any opamp in the IC. Method: Use several R1 and R2 configurations and change your input voltage and record your output voltage. (EXPLAIN with a TABLE)

Vin (V)	Vout (V)	R1 (Ω)	R2 (Ω)
0.097	0.293	1k	2k
1.06	3.2	1k	2k
2.11	6.37	1k	2k
3.13	8.63	1k	2k
4.15	8.63	1k	2k
5.27	8.63	1k	2k
6.09	8.63	1k	2k
7.21	8.63	1k	2k
8.03	8.63	1k	2k
9.1	8.63	1k	2k
9.99	8.63	1k	2k
0.097	0.147	2k	1k
1.04	1.58	2k	1k
2.36	3.57	2k	1k
3	4.55	2k	1k
4.44	6.73	2k	1k
5.42	8.22	2k	1k
6.25	8.64	2k	1k
7.18	8.64	2k	1k
8.32	8.64	2k	1k
9.16	8.64	2k	1k
10.02	8.64	2k	1k
0.097	0.118	4.7k	1k
1.31	1.61	4.7k	1k
2.37	2.89	4.7k	1k
3.05	3.73	4.7k	1k
4.05	4.95	4.7k	1k
5.08	6.21	4.7k	1k
6.23	7.621	4.7k	1k
7.02	8.59	4.7k	1k
8.03	8.68	4.7k	1k
9.1	8.68	4.7k	1k
10.05	8.68	4.7k	1k

When we were deciding on our resistors we took into account the gain equation so we could show the different kinds of gain that we measured by having a smaller R2 versus a smaller R1.  We decreased R2 so that we could have more measurements before we met the threshold.

2.       Use your temperature sensor as your input. Do you think you can generate enough voltage to trigger the relay? (EXPLAIN)

Yes, we believe we can get enough voltage from the amplifier to get the relay to switch.  We calculated the gain using the equation for a non-inverted amplifier to figure out what R2 and R1 configuration would best get us close enough to the approximately 5.22V we would need to get the relay to switch. 

3.       Design a system where LED light turns on when you heat up the temperature sensor. (CIRCUIT schematic and explanation in a VIDEO)

A drawing of our circuit.

A video showing how our circuit is set up

A video showing our LED turning on

4.       BONUS! Show the operation of the entire circuit. (VIDEO)

A video showing how our circuit is set up

A video showing our relay switching from one LED to another LED