Lab Team 4 Week 6 (15 - 21 February)

Operational Amplifier

(Op-Amp)

1. You will use the Op-Amp 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 -5 V to 5 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 V_in). Discuss your results. What would be the ideal plot?

In this open loop configuration the Op-Amp will Function as a comparator.  The Op-Amp's output will be equal to the V+ input if the Non-Inverting (+) input is grater that the Inverting Input (-).  An Ideal Model of this Circuit would see an output of +5V for any positive input, 0V if 0V is input, and -5V for any Negative input.  But because our circuit is not a theoretical model there is a small loss between our V+/V- inputs and our V-out output.  This leaves us with an output range of [-3.63, 4.46] Volts.  Additionally under ideal circumstances we would have achieved a 0V output when 0V was present at terminal (-).

Open Loop Non-Inverting Input vs Output Voltage

  b. Apply 0 V to the non-inverting input. Sweep the inverting input (V_in) from -5 V to 5 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?

   As stated in 1A this Op-Amp is again acting as a compatator.  When a positive voltage is applied to the Inverting Input (-) the Op-Amp's output is negative because:

Voltage at terminal (-) is greater than voltage at terminal (+)

   

   Similarly when a negative voltage is applied to terminal (-) the Op-Amp's output is positive because:

Voltage at terminal (+) is greater than voltage at terminal (-)

   If out circuit achieved ideal results the output range would be 

   [-5, 5] instead of the [-3.7, 4.45] that we achieved.  Additionally under ideal circumstances we would have achieved a 0V output when 0V was present at terminal (-).

Open Loop Inverting Input vs Output Voltage

2.     Create a non-inverting amplifier. (R₂ = 2 kΩ, R₁ = 1 kΩ). Sweep V_in from -5 V to 5 V with 1 V steps. Create a table for V_in and V_out.  Plot the measured and calculated data together. 

    When we constructed the Non-Inverting Amplifier as described above according to a theoretical model we should have been able to achieve a gain of 3x as calculated (1+R2/R1) surprisingly at +1V and -1V inputs we actually exceeded this the ideal gain with outputs of 3.07 and -3.23 Volts.  Our Minimum/Maximum outputs, however; did not achieve the ideal Minimum/Maximum output range of [-5, 5] Volts as our range was [-3.58, 4.19] Volts.

The Data we collected from this circuit is displayed in the 

Table and Scatter Plot below

 

Data from our Non-Inverting Amplifier Circuit including Ideal (Theoretical) and Actual Gain

 

Non-Inverting Amplifier:  Non-Inverting Input vs Output Voltage

3. Create an inverting amplifier. (R_f = 2 kΩ, R_in = 1 kΩ). Sweep V_in from -5 V to 5 V with 1 V steps. Create a table for V_in and V_out. Plot the measured and calculated data together.

   When we constructed the Inverting Amplifier as described above according to a theoretical model we should have been able to achieve a gain of 2x as calculated (1+R2/R1) surprisingly at +1V and -1V inputs we actually achieved or exceeded this the ideal gain with outputs of -2.24 and exactly 2.00 Volts.  Our Minimum/Maximum outputs, however; did not achieve the ideal Minimum/Maximum output range of [-5, 5] Volts as our range was [-3.49, 4.16] Volts.

The Data we collected from this circuit is displayed in the 

Table and Scatter Plot below 

Data Collected from our Inverting Amplifier Circuit to include Ideal (Theoretical) and Actual Gain

Inverting Amplifier:  Inverting Input vs Output Voltage  Plot

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

In the open loop configuration the Op-Amp does not actually act as an amplifier, but functions essentially as a comparator.  If the Non-Inverting (+) input Exceeds the Inverting (-) input it's output is equal to whatever voltage is present on the V+ input.  Conversely if the Inverting (-) input Exceeds the Non-Inverting (+) input it's output is equal to whatever voltage is present on the V- input. 

It is only when connecting to a larger circuit with a pair of resistors that the Op-Amp can actually act as an amplifier.  Of the two possible configurations (Inverting and Non-Inverting) the Non-Inverting Amplifier achieves a slightly smaller gain calculated as 1(R2/R1) while an Inverting Amplifier only achieves a gain of -1(R2/R1). 

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).


      As the Data we collected in the table below demonstrates our temperature sensor acts as a variable resistor as with resistance decreasing as temperature increases.  To test the sensor we connected it to a 5V power source and read it's output voltage at room temperature, squeezed between my fingers for body heat, and when exposed to a standard Hair Dryer on the high setting.

Relay:

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

  
    With no voltage present on pin 2 of the relay continuity exists between pins 1 and 4, this is not surprising because in it's de-energized position a closed contact connects pins 1 and 4.  These contacts remained closed as we applied an gradually increasing voltage to pin 2 until we reached 6V at which time the relay energized breaking the circuit, at which point the Ohm-meter read OL.

    The opposite is true when reading the voltage from pin 1 to pin 3.   When 0-5 Volts an open circuit existed between the pins with the Ohm-meter reading OL, then when as the Voltage on Pin 2 was increased to 6 Volts the Relay energized closing the contacts between Pins 1 and 3 creating continuity.

The exact readings measured across Pins 1&3 and Pins 1&4 can be seen on the table below.

   
    2. Now sweep your DC power supply from 0V to 8V and back to 0V. What do you observe at the multi-meter (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).

Chris Explains the operation of our relay as voltage on pin 2 in cycled from 0-8 VDC   

  We found the Relay had a Threshold Voltage of about 6 Volts and when it was reached we could hear an audible click as it energized.  We heard the clicking again when we turned the Voltage down to   2 Volts and the Relay De-Energized.

    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 relay operates by using an electro-magnetic coil to actuate one or more internal switch(s).  This is useful because a relatively small voltage can be used to control the relay, which in turn can then be used connect/disconnect a different voltage source to components as needed.  A common use for a relay to use a low amperage DC power source to control a high amperage AC power source.
 

Kevin Explains Basic Relay Operation

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 Simple Control Relay Circuit connected to an LED

Kevin demonstrates the circuit's operation

Operational Amplifier

   1.     Connect the power supplies to the op-amp (+10V and 0V). Show the operation of LM 124 operational amplifier in DC mode with a non-inverting amplifier configuration. Choose any Op-Amp in the IC. Method: Use several R1 and R2 configurations and change your input voltage (voltages between 0 and 10V) and record your output voltage. (EXPLAIN with a TABLE)

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

  The temperature sensor can't produce enough voltage to trigger the relay on its own, however the voltage could be amplified with an Op-Amp to a reach the relay's threshold. 

  The relay needs about 6 volts to actuate, and the temperature sensor can only put out about 1.4 volts even when exposed to our heat source's maximum output. A non-inverting Op-Amp can amplify that voltage from 1.4 volts to 6 volts easily, triggering the relay. 

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

Kevin explains the final circuit setup.

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

Chris Demonstrates our Final Circuit in Action.

Week 5 8-14 February 2016

During this week's lab we work with an Oscilloscope and Function Generator along with a transistor on an integrated circuit.

      1. Functional check: Oscilloscope manual page 5. Perform the functional check (photo).

First we performed an a Functional Check on the Oscilloscope as outlined on page 5 of the Oscilloscope Manual.

Testing a 10x Oscilloscope Probe as part of the Functional Check. 

      2. Perform manual probe compensation (Oscilloscope manual page 8) (Photo of overcompensation and proper compensation).

During the Functional check we discovered we found one of our probes was out of calibration, so we performed manual probe compensation in accordance with the Oscilloscope Manual Page 8. 

Manual Probe Compensation Photos

Probe in a state of overcompensation.

Probe reading after proper calibration.

      3. What does probe attenuation (1x vs 10x) do (Oscilloscope manual page 9)?

Some probes have multiple attenuation settings that can be selected using a mechanical switch on handle of the probe.  It is important to insure the setting you select matches the setting on the Oscilloscope.  The attenuation settings change the impedance through the probes you are using, allowing a more accurate reading.  If your probes settings do not match those of your Oscilloscope you will be unable to utilize the machine's full bandwidth potential.   

      4. How do vertical and horizontal controls work? Why would you need it (Oscilloscope manual pages 34-35)?

Prior to starting this week's experiment we took some time to familiarize ourselves with the oscilloscope's controls.  Our particular oscilloscope has two separate input channels and the control panel allows the user to choose whether to display data from either channel individually or both channels simultaneously.  

The Horizontal and Vertical controls operate similarly to the controls on an old tube style television and allow you to control where the data is displayed on the screen.  This is especially useful when displaying data from both channels as you can choose to either separate the data on different parts of the screen or directly overlay both channels data atop one another for easy comparison.

The Scale controls are also important as they allow the user to either expand or condense the data being displayed as needed to take proper reading.

Another important control is the Auto Set button which displays the scales the data on the display in an "optimized" manner with the press of a single button.  While it is not always exactly what is called for it provides a good starting point for finer adjustment.  

Also in conjunction with the Measure button the five buttons to the immediate right of the O-scope's screen allow the user to customize the information on the display.    

     5. Generate a 1 kHz, 1 Vpp around a DC 2 V from the function generator (use the output connector). DO NOT USE oscilloscope probes for the function generator. There is a separate BNC cable for the function generator.

a.       Connect this to the oscilloscope and verify the input signal using the horizontal and vertical readings (photo).

b.      Figure out how to measure the signal properties using menu buttons on the scope.

Our first task was to connect our function generator to our O-Scope and attempt to generate a 2VDC/RMS signal.  Our instructions indicated we should have been able to accomplish this by generating 1 kHz / 1Vpp signal but even after increasing our output to amplitude to 2V (4Vpp) we were only able to achieve 1.50 V RMS 

Function Generator putting out a 1 kHz 4Vpp Signal

Despite increasing our input voltage up to 4Vpp we were only able to achieve 1.50 V RMS

Note the RMS data displayed on the right hand side of the screen.  The data displayed is customizable using the Menu/Measure buttons.  In this case we selected Min/Max and Cycle/Cursor RMS Voltages.

  

      6. Connect function generator and oscilloscope probes switched (red to black, black to red). What happens? Why?

In accordance with the lab instructions we reversed the the black and red leads on the O-scope probe, while we expected to see a the waveform reverse, but instead the oscilloscope only displayed a flat zero volt signal.  

We believe the reason for this that according to the O-scope manual (page v) the ground lead is at ground potential.  Because of this the signal goes directly to ground and bypasses the oscilloscope's measurement circuitry.

7.  After calibrating the second probe, implement the voltage divider circuit below. Measure the following voltages using the Oscilloscope and comment on your results:

&

8. For the same circuit above, measure V_a and V_b using the handheld DMM both in AC and DC mode. What are your findings? Explain.

Circuit 7 & 8 Schematic

When attempting to implement the circuit below we were unable to achieve an input of .5 VAC/5 VDC utilizing our function generator.
We ended up using an input amplitude of 1.5 Volts with an offset of +3.72 Volts.  When we attempted to either increase the offset or input amplitude the function generator gave a warning message.

The data we collected for Steps 7&8 is below 

When taking our readings voltage division between the three resistors worked as expected with all three resistors dropping between 102-106 mV.  The measured RMS voltage as measured by the O-Scope was almost exactly one -tenth of the DMM's VDC reading.  While the DMM's AC reading was approximately equal to the O-Scope's V-RMS reading multiplied by sqrt(2).

      9.       For the circuit below

a.       Calculate R so given voltage values are satisfied. Explain your work (video)

b.      Construct the circuit and measure the values with the DMM and oscilloscope (video). Hint: 1kΩ cannot be probed directly by the scope. But R6 and R7 are in series and it does not matter which one is connected to the function generator. 

Step 9 Schematic Diagram

We Calculated the Resistance using the following Steps

    1.) Multiply 5V (RMS) by Sqrt 2 to Get an input Voltage of of 7.07 Vpp

    2.) Calculate VR7 by subtracting VR6 from the 7.07V input.  VR7=5.07 Vpp

    3.) Calculate R7 using the equation R7 = R6(VR7/VR6)

    4.) R7 = 2535 Ohms or 2.5 Kilo-Ohms 

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This is a short video describing how we calculated our R7 value for the given circuit.

This video chronicles the readings taken of circuit as requesting in step 9B, which confirmed the calculations we made in step 9A

      10.   Operational amplifier basics: Construct the following circuits using the pin diagram of the Op-Amp. The half circle on top of the pin diagram corresponds to the notch on the integrated circuit (IC). Explanations of the pin numbers are below:

a.       Inverting amplifier: R_in = 1kΩ, R_f = 5kΩ (do not forget -10 V and +10 V). Apply 1 V_pp @ 1kHz. Observe input and output at the same time. What happens if you slowly increase the input voltage up to 5 V? Explain your findings. (Video)

b.      Non-inverting amplifier: R₁ = 1kΩ, R₂ = 5kΩ (do not forget -10 V and +10 V). Apply 1 V_pp @ 1kHz. Observe input and output at the same time. What happens if you slowly increase the input voltage up to 5 V? Explain your findings. (Video)

Circuit 10 A (Inverting Amplifier) Schematic

Chris Explains the data we collected from the Inverting Amplifier.
A complete breakdown of this data can be found in the Table Below.

Circuit 10 B Schematic

Chris Explains the data we collected from the Non-Inverting Amplifier.
A complete breakdown of this data can be found in the Table Below.

Week 4: 1-5, February 2016

  1.     (Table and graph) Use the transistor by itself. The goal is to create the graph for I_C (y axis) versus V_BE (x axis). Connect base and collector. Use 10K potentiometer to generate the voltage. Use 5 V but DO NOT EXCEED 1 V for V_BE. Make sure you have the required voltage value set before applying it to the base. Transistor might get really hot. Do not TOUCH THE TRANSISTOR! Make sure to get enough data points to graph. (Suggestion: measure for V_BE = 0V, 0.5V, and 1V and fill the gaps if necessary by taking extra measurements). The circuit should look like below:

Circuit 1 Schematics

With the circuit setup in accordance with the schematic above, we were able to use the 10k potentiometer to apply various voltages to the base of the transmitter.  As the voltage increases from 0-0.6V there is only a slight increase in current at the Collector Node.  When the voltage increases to 0.65V the current begins to increase exponentially reaching a peak of 4.18 mA when we stopped the experiment at 0.66V to prevent potential damage to the transistor.

This table shows the values we recorded for VBE and IC

Chart showing the Exponential increase in Current at the Transistor's Collector Node as Voltage at the Base increases past its trigger point.

  2.     (Table and graph) Create the graph for I_C (y axis) versus V_CE (x axis). Vary VCE from 0 V to 5 V. Do this measurement for 3 different VBE values: 0V, 0.7V, and 0.8V. The circuit should look like below:

Circuit 2 Schematic

This table above displays the values we found for this particular experiment.

With 0 Volts present at the Transistor Base only 1 mA of Current was present at the collector base

With 1 Volt present at the Transistor Collector Current increased gradually from 0 to 14.8 mA as the Base voltage increased from 0 to 0.7v between 0.7 to 0.8v the current began increase exponentially peaking at 79.2.

With 2 Volt present at the Transistor Collector Current increased gradually from 0 to 29.3 mA as the Base voltage increased from 0 to 0.7v between 0.7 to 0.8v the current began increase exponentially peaking at 142.

With 4 Volt present at the Transistor Collector Current increased gradually from 0 to 23.8 mA as the Base voltage increased from 0 to 0.7v between 0.7 to 0.8v the current began increase exponentially peaking at 272.

  
  3.     (Table) Apply the following bias voltages and fill out the table. How is I_C and I_B related? Does your data support your theory?

I_C and I_B are related by beta, which is equal to I_C divided by I_B . For example, if beta was equal to 100, that would mean that whatever the current for I_B was, the the current for I_C would be 100 times greater. Our data did not support this. We believe that our transistor was damaged in the previous circuit, yielding us inaccurate results. 

  4.     (Table) Explain photocell outputs with different light settings. Create a table for the light conditions and photocell resistance.
   
    A photocell provides different resistance values depending on the amount of light that it receives. The more light it receives, the less resistance it supplies. Our data we collected supports this.

This table illustrates the resistance value measured across the Photo Sensor under various lighting conditions. 

  5.     (Table) Apply voltage (0 to 5 V in 1 V increments) to DC motor directly and measure the current using the DMM.

This table illustrates the current drawn by the motor as the voltage increases from 0-5V in 1 volt increments. 

  6.     Apply 2 V to the DC motor and measure the current. Repeat this by increasing the load on the DC motor. Slightly pinching the shaft would do the trick.

    With 2 volts applied increasing pressure was applied to the shaft of the motor.  The amount of current being drawn increased from 36.1 mA with no load applied, to 97.3 mA at the point sufficient pressure was applied to stop the motor. 

The table above shows the current being drawn by the electric motor as various amounts of pressure are applied to the spinning shaft.

  7.     (Video) Create the circuit below (same circuit from week 1). Explain the operation in detail.

Rube Goldberg Circuit Schematic

The Circuit above operated by using a photo sensor in conjunction with a 1k W resistor to control the voltage present at the base of the transistor.  A second power supply provides power to the transistor's collector node.  As the light intensity increase the photo sensor's resistance decreases, this increases the voltage present at the transistor base, allowing voltage to flow from the Collector to the Emitter providing power to the motor.

Video of the rebuilt Rube Goldberg Circuit in action.

 
  8.     Explain the 47 Ohm Resistor's role by changing its value to a smaller and bigger resistors and observing the voltage and the current at the collector of the transistor.

  The 47 Ohm resistor in the Rube Goldberg circuit serves as a buffer that prevents excessive current from the power supply from damaging the transistor.  Ohm's Law dictates the if the buffer's resistance is doubled the current value is halved, and if the resistance is halved the current will double.  This prediction is confirmed by the data we collected which can be seen on the table below.

Chart of Current and Voltage present at the Transistor's Collector Node.  

  9.     (Video) Create your own Rube Goldberg Setup.

  Our team's approach to the Rube Goldberg circuit is to utilize the a paddle attached to the motor to knock over a Formation of Dominoes that can then be used to trigger the next portion of the circuit. 

A successful test of our Rube Goldberg Circuit knocking over a Formation of Dominoes

* Video of our previous "failed" tests are posted on our Lab Team's You Tube Channel at

Lab Team 4 on YouTube