===== Related reading ===== Hayes and Horowitz: Pages 25 - 34 [[https://www.physics.dcu.ie/~bl/anacont.html|Lawless]]: Chapters 1 - 4 [[https://doctor-pasquale.com/books/|Pasquale]]: Pages 31 - 54 ====== Goals ====== ---- In the first lab, you will become acquainted with a set of standard tools that are used for building and testing electronic circuits.  These include: - {{ phylabs:lab_courses:remote_courses:phys-226-wiki-home-remote:spring2020-lab-1-dc-circuits:tektronix_oscilloscope_manual.pdf | Tektronix TBS1052 Two-Channel Digital Storage Oscilloscope }} - {{ phylabs:lab_courses:remote_courses:phys-226-wiki-home-remote:spring2020-lab-1-dc-circuits:rigol_function_generator_manual.pdf | Rigol DG800 Dual Channel Function Generator }} - Electronics breadboard (or protoboard) In addition, you will be using a variety of test leads and coaxial cables to make connections between test devices and the circuit you are working on. ** Electronics vs Physics Labs ** In most of the instructional lab courses on physics, the focus has (broadly) been using evidence to make conclusions about physical systems. The electronics course has a different goal: for you to learn enough about circuit design and functionality to start to be able to understand and design circuits in service of doing experimental physics. As such, the structure of the course will be markedly different that what you've seen before. * ** Labs are numerous and hands-on ** Due to the overhead needed to get to building functional circuits, there will be 16 lab periods throughout the quarter. The first labs in particular will have more guided exercises to help you get a solid foundation in circuit behavior and how to use the test & measurement equipment. * ** Lab writups will be minimal ** As the focus is on building, testing, and designing circuits, you aren't expected to write extensive reports. What you are asked to submit is a short document typically covering key observations. * ** Uncertainty analysis has no place here ** While it is certainly possible to perform uncertainty analysis on circuit behavior, it is unlikely to be helpful for this course. The issues you encounter are usually either enormous (improper connections or incorrect components for example) or very subtle (capacitive behavior in diodes or bandwidth limitations on test instruments) that they are unlikely to be explained by analyzing uncertainties. * ** Failure is always an option ** It will not be uncommon to observe a circuit malfunction because you haven't built it correctly, or because you've made mistakes (or unwarranted assumptions) involving the test & measurement equipment. This still happens to experienced designers, and as you get more experienced you'll be able to troubleshoot problems more quickly.
Pros at work {{:phylabs:lab_courses:phys-226-wiki-home:fasterdumb.jpg|}}
* ** Troubleshooting is an integral part of design ** Since things may not work the first time, you'll have to figure out both why they aren't behaving as expected and how to fix them. [[phylabs:lab_courses:phys-226-wiki-home:troubleshooting:start|Some general guidelines can be found here]]. * Before you ask your TA for help, you should be able to provide some more specific information than "It isn't working." * ** Predictions are important ** As a corollary to the previous point, you need to know what a circuit is supposed to do to figure out if it isn't doing it. Sometimes you can make very specific predictions (e.g. //"The amplitude should be cut in half when we increase the frequency to 39 kHz"//) and other times you might have broader predictions (e.g. //"I should see the voltage change when I turn on the function generator"//), and when you're really struggling to figure out things you might fall back to extremely basic things (e.g. //"It should behave differently when I turn the power off"// or //"touching a resistor shouldn't do anything"//). ===== Lab Submission ===== For each lab, a template containing guiding questions will be provided to you.  You should also keep a lab notebook as a way of recording what you do and why, but it will not be assessed by your TA. Questions may appear in the webpage that are not reflected in the template.  You don't have to document anything related to said questions, but they are there to guide you in thinking about electronics in a more expert fashion.  The hope is by the end of the course you'll start asking yourself such guiding questions without prompting, but until then such questions will provide you with support.
[[https://docs.google.com/document/d/1ic_oYg_lz6qATMn0vEfZv9e9-iT5Cc_5ToFX1bRLQn8/copy|Lab Template]]
Every lab has a template to go with it, similar to our intro courses. The focus on this course is more on the process of building & testing circuits more than making particular measurements. We want students to learn enough to build on later when they need to interface devices in the lab, not test the predictions physics makes about circuit behavior. ===== On Wiki Formatting ===== Since a good portion of this lab will feature guided activities, we've set up a system to help differentiate information from instructions from rhetorical questions. Information and general background has no special formatting Rounded grey boxes are used to denote instructions: What you need to physically do as you proceed through the lab. > Text that's offset like this is used to indicate points to test or consider. Not all such instructions need to be recorded in your report, but you should be able to answer them as you go through the lab. They will help you gauge how much you're absorbing the content of the class.
Sometimes there are clickable notes in bold text These notes typically: * Instructions on how to do something specific that not everyone will need, * Longer derivations of mathematical terms for the curious, or * Bits of supplementary information/trivia/history that aren't strictly necessary.
**[[phylabs:lab_courses:phys-226-wiki-home:electronics_vocabulary| Some electronics jargon will have clickable or hoverable links to explain new terms more fully]]** ====== Exploring the basic setup ====== ---- Throughout the semester, we will be wiring circuits on a standard electronics breadboard or protoboard.  In addition, we will typically be using the regulated power supply to provide a DC voltage for our circuits. In this section, you will use the digital multimeter (or DMM) to investigate the breadboard and the power supply.
| {{phylabs:lab_courses:phys-226-wiki-home:spring2020-lab-1-dc-circuits:multimeter.png?600|}} | | Your digital multimeter, with minigrabber leads. You will need to turn the knob to the yellow $\Omega$ symbol to measure resistance. |
==== Exploring the breadboard.   ==== A
breadboard
{{page>phylabs:lab_courses:phys-226-wiki-home:electronics_vocabulary#breadboard&nouser&nodate}}
like the one we'll use in this course is shown below.  Explore the interconnections between various points on the breadboard using your DMM in resistance mode (Ω).  A low reading shows an electrical connection while a very large reading or overload (OL) message indicates that there is no connection.  **//Note that the leads on the DMM do not fit into the breadboard holes; you will need to use jumper wires from your kit to connect the meter to the breadboard.//** Using your multimeter, explore the connectivity of the breadboard. You'll be using it throughout the entire course, so taking some time now to really understand its layout can help save you time later when you're building circuits. > Make sure that you understand how the contact points are connected, paying particular attention to the vertical running holes on the sides of each board segment and to the horizontal running holes at the top of the board. These points are often used as a
power bus
{{page>phylabs:lab_courses:phys-226-wiki-home:electronics_vocabulary#bus&nouser&nodate}}
to bring power and ground close to your components.  The report template has an editable breadboard schematic for you to annotate.
| {{phylabs:lab_courses:phys-226-wiki-home:spring2020-lab-1-dc-circuits:breadboard.png?400|}} | {{phylabs:lab_courses:remote_courses:phys-226-wiki-home-remote:spring2020-lab-1-dc-circuits:breadboard_diagram.jpg?0x400|}} | | A photo of the breadboard you have for this course.  Note that this has six identical modules on the lower portion. | A schematic of one of the six modules on the main breadboard.  Click on the image for a larger version to annotate or download. |
There are 3 key parts that are good for students to observe here: - The vertical series of holes on the edges only connect vertically - The horizontal series of holes in the middle only connect horizontally - There is a break in the connectivity of the horizontal hole set across the middle gap You can illustrate the reason for that with any of the IC chips around the room; they're spaced to perfectly straddle the gap. If there wasn't a break across the middle, then every pair of pins across the chip would short to one another. ==== Exploring the power supply ==== The triple DC power supplies used in this lab (shown below) can each produce two independent variable DC voltages (with maximum voltage and maximum current settings) as well as a constant 5 V output. When using the variable supplies, they will typically be used as constant voltage sources and the currents drawn will usually be on the order of mA. Given that the supplies are capable of supplying 3 A of current, it is a good idea to set the current limit to approximately 0.5 A (1/6 of the total current range) or less; you can do this by turning the current knob fully counter-clockwise and then adjusting it clockwise by about 3 or 4 small gradations.
| {{:phylabs:lab_courses:phys-226-wiki-home:lab_1_dc_circuits:power_supply.png?600|}} | | Our benchtop power supplies. Note that the knobs and indicator lights are mirrored from left to right channels. |
What if I want more precision? To set a precise limit, you can short the terminals with a wire while adjusting the current limit knob. Note that this is a terrible idea if you are working with an unknown device! Always check the manual unless you are keen on voiding warranties or starting fires.
It is important to note that the power supply is floating supply; a setting of 5 V only tells us that the potential difference between the two supply terminals is 5 V. It says nothing about how either potential compares to ground (0 V). In order to set one of the terminals to ground, you must connect that terminal (and that terminal alone) to ground (green GND label) using a banana cable or some other type of connector. Configure your power supply such that there is a 3 V difference between the red and black terminals, and set up a multimeter to verify this. Then, use a cable to connect the black terminal to the green one (ground) and use the multimeter to measure the differences across the terminals as well as the difference between ground and the other two terminals. Finally, connect the red terminal to ground and repeat. > Did the connection to ground change the potential difference between the terminals? The reading between terminals shouldn't change here unless something's gone horribly wrong. Selectively grounding the negative or positive terminal is how we can select if we want a positive or negative voltage from the supply. It didn't matter much in intro courses, but semiconductor devices can be permanently damaged or destroyed by flipping the sign of voltages. Thankfully, all the parts we're working with are cheap.
How do I connect wires to the terminals?
| {{phylabs:lab_courses:phys-226-wiki-home:spring2020-lab-1-dc-circuits:bananaconnectors.png?240|}} | {{phylabs:lab_courses:phys-226-wiki-home:spring2020-lab-1-dc-circuits:bananaconnectorsright.png?240|}} | {{phylabs:lab_courses:phys-226-wiki-home:spring2020-lab-1-dc-circuits:bananaconnectorswrong.png?240|}} | | To connect the power supply to the breadboard, unscrew one of the banana jack connectors at the top of the board. | When re-tightening the connector, make sure that only exposed metal is in the hole. | Don't tighten the connector on the insulation; even if it works some of the time it will cause intermittent problems. |
When in doubt, measure! Students can always use a multimeter to test if their connections are being made properly. In this instance, detaching the power supply and measuring the resistance from the wire to socket will tell them if they've made a good connection or not. Wiggling wires while testing can help identify poor connections that can otherwise be hard to spot, such as in the case in the expandable section above on the right. There can also be issues where the wire has become brittle and the end has snapped off, but it still looks like it is connected at a glance. ====== Your first circuit ====== ---- During the first few weeks of the course, we will cover voltage divider circuits extensively.  In this lab, we are asking you to build a simple voltage divider circuit to gain experience with assembling circuits on the breadboard.  Consider the circuit shown in Fig. 1. //Predict// whether the absolute value of $V_{out}$ will be //greater than//, //less than//, or //equal to// the voltage of the power supply, +3 V.  Write your prediction in your report, and briefly explain.  **On Predictions** Making predictions is more important when working with electronics than typical labs.  You can't see what's happening in circuits directly, so if you don't have some expectations for how something //should// behave it is hard to tell if it is doing what it is supposed to or if there is a problem.  Sometimes predictions can be as simple as //"If I disconnect the input I should see 0V at the output,"// or //"If I wiggle a cable nothing should change."//  These basic low-level predictions are at the heart of troubleshooting circuits, which you will inevitably need to do during this course.
| {{:phylabs:lab_courses:phys-226-wiki-home:lab_1_dc_circuits:voltage_divider_full_3x.png|}} | {{:phylabs:lab_courses:phys-226-wiki-home:lab_1_dc_circuits:voltage_divider_fast_3x.png}} | | **Figure 1:** A basic voltage divider circuit. || | The circuit shown in a traditional format from PHYS 132/142 courses. Note that the open white circles indicate points that are being measured across. | The same circuit depicted in a compact notation. $V_{out}$ is still measured with respect to ground, and the more negative terminal of the power supply is also connected to ground. | | [[https://digilent.com/blog/why-do-electronic-components-have-such-odd-values/ | Why 22k instead of 20k?]] ||
===== On Building Circuits Well ===== Circuit diagrams are a different kind of thing than free-body diagrams or field diagrams or ray diagrams or even engineering blueprints. The diagram only concerns itself with the electrical topology, i.e. which parts of circuit elements are electrically connected to other elements. The circuit elements themselves are also abstract; even something as simple as a resistor can have multiple representations, none of which look like the part itself (as shown below). The parts themselves even come in a variety of physical packages. Let's think a moment about how we can go about building circuits in a somewhat systematic way.
| {{phylabs:lab_courses:phys-226-wiki-home:lab_1_dc_circuits:resistor_variants.png}} | | Two symbols and one photo of a 1 k$\Omega$ resistor. The left symbol is more common in US and physics contexts, the box symbol is more prevalent in the EU and engineering contexts. |
Looking at our diagram in figure 1, we can first note that there are only 2 components and a power supply needed. The diagram on the right also makes it clear that there are only three junctions(nodes) in the circuit * 3V to one side of the 22k resistor * 0V to one side of the 10k resistor * The other sides of the resistors to each other We're going to use a hybrid diagram to show you how you would conventionally go about building the circuit. This isn't something you'll likely see in the wild, it's just a tool for starting out. ==== Connecting Power ==== In the vast majority of circuits, you'll have some voltage that's used to power things. In our case, it will be +3V from the power supply. To start you'll want to use a cable to connect the positive side of the power supply to one of the jacks at the top of the board. Then, using the wire connected to the jack, make the following connections: * Connect the wire to one of the bus strips at the top of the breadboard * Use a wire to connect the horizontal bus strip to one of the vertical ones * Use one more wire to jumper over from the bus strip to the body of the breadboard
| {{phylabs:lab_courses:phys-226-wiki-home:lab_1_dc_circuits:breadboard_step_1.png}} | | The first step of making your circuit. Note that all new connections/parts will be shown in purple. |
Next, connect a resistor between two separate rows on the breadboard. You'll need to bend the metal legs to make it fit where you want it.
| {{phylabs:lab_courses:phys-226-wiki-home:lab_1_dc_circuits:breadboard_step_2.png}} | | Inserting the 22 k$\Omega$ resistor in the breadboard. A very common mistake is to have one end above or below the row you want. |
Third, insert the 10 k$\Omega$ resistor with one lead in the same row as the 22k and the other in a different row.
| {{phylabs:lab_courses:phys-226-wiki-home:lab_1_dc_circuits:breadboard_step_3.png}} | | Placing the 10k resistor. Again, make sure the rows line up right. |
Fourth, we'll wire up a connection to ground to complete the circuit.
| {{phylabs:lab_courses:phys-226-wiki-home:lab_1_dc_circuits:breadboard_step_4.png}} | | Placing the 10k resistor. Again, make sure the rows line up right. |
Lastly, we'll insert a pair of wires to grab with the multimeter or oscilloscope.
| {{phylabs:lab_courses:phys-226-wiki-home:lab_1_dc_circuits:breadboard_step_5.png}} | | Wires added for measurement purposes. Note that they only have one connection, electrically they might as well not be there. |
You're now just about ready to connect your meter, turn on the power supply, and start measuring. **Circuit Conventions** There are some conventions to how circuits tend to be drawn that aren't really explained in introductory texts. When possible, designs tend to have powering voltages arranged from top to bottom (i.e. ground connections or negative voltages go at the bottom of the diagram) and signals propagate from left to right. It's sort of similar to how many maps have north towards the top and east to the right. It makes it easier to orient yourself when looking at a new map, and similarly these conventions make it easier to interpret schematics. === Implemented Example === The photo below shows examples of how you could've gone about building the same circuit, with decreasing levels of cursedness as you go from left to right.
| {{:phylabs:lab_courses:phys-226-wiki-home:lab_1_dc_circuits:breadboardexamples.png?800|}} | | Four examples of the same circuit. All are topologically identical, but the building style on the right (utilizing the power rails, laying out parts along clear & straight lines, etc.) is preferable for working on larger projects. |
You'll see far messier layouts than this as the quarter goes on. For the messier ones, it can help if you ask students to help you trace through the circuit with you when you're troubleshooting (e.g., asking "Where is the connection to +3 V? What does that connect to?"). Even if you can instantly see that something is off by a hole on the breadboard, taking the time to help students find that helps them learn how to find issues themselves. Use your judgement on this; if somebody is horribly frustrated then a quick fix to let them get moving again may help more than an extended troubleshooting session. ==== Connecting to the voltage divider circuit. ==== Turn on your power supply and check your prediction by reading out the voltage on your multimeter. > Be sure to record what you measured and reconcile your observations with your prediction. Adjust the voltage of your power supply throughout the range of values available to you, and observe the effect on the circuit's output $V_{out}$ > Does the voltage divider behave the same way (i.e. divide voltage by the same fraction) as the voltage varies? These power supplies go up to around 32V or so (it varies), but the ratio of $V_{out}$ to $V_{in}$ should be about $\dfrac{10k\Omega}{10k\Omega + 22k\Omega} = \dfrac{1}{3.2} \approx .313$. This is based on the nominal (stated) resistor values, which can be off from the actual values by 5% for our resistors. In that case, the worst case scenarios are $\dfrac{V_{out}}{V_{in}} = \dfrac{10.5}{10.5+20.9} \approx .334$ or $\dfrac{V_{out}}{V_{in}} = \dfrac{9.5}{9.5+23.1} \approx .291$ If things are further off than that, then I'd suggest you measure the actual resistor values to make sure that previous students didn't mix the values into the wrong place. Leave your circuit built, you'll be coming back to it later. ====== Part 2: Using the Oscilloscopes ====== ---- {{page>phylabs:lab_courses:phys-226-wiki-home:scope-skills:start&nouser&nodate}} ====== Part 3: AC Voltage Division ====== ---- Okay, now that we're up to speed on using an oscilloscope, let's apply this knowledge to our actual circuit ===== Applying a sinusoidal input voltage to the voltage divider circuit ===== Use a BNC-to-paired-banana-plug adapter and two banana cables to connect the Channel 1 output from the function generator to the voltage divider, replacing the DC power supply as shown in Fig. 2. The BNC connector should slide in gently, and lock when it rotated when it is turned about a quarter of a turn clockwise. The outer conductor of the BNC cable is grounded, and you will need to ensure that the grounded (black) lead from the function generator is connected to the grounded output terminal in the circuit.
| {{:phylabs:lab_courses:phys-226-wiki-home:spring2020-lab-1-dc-circuits:lab1_fig2_01.png?400|}} | | **Figure 2:** An AC voltage divider |
==== Measuring signals with the 10X probe. ==== Your 10X scope probe attenuates the measured voltage signal to 1/10th of its size.  Thus the signal must be digitally multiplied by a factor of 10 (10X) in order to accurately display the measured voltage at the tip of the probe.  The scope is configured to do so normally, and for this course the 10X probe is suitable for routine measurements.
Why would we do this? The 10x probe has a compensating capacitor that lets it accurately display signals on a much quicker time scale than would be possible just using wires.  If we were to use only a regular coaxial cable, then we would start to see distortions on a time scale of 10s of nanoseconds; this is enough to distort many digital signals. 
Connect the probe tip to the $V_{out}$ wire on your breadboard, and connect The smaller ground lead (which has an alligator clip) to ground. If you flip these, you'll see little if any signal. 
| {{phylabs:lab_courses:phys-226-wiki-home:spring2020-lab-1-dc-circuits:scope-probe.png?400|}} | | A 10x probe, ready to be used to measure signals. |
> Is the output you observe what you’d expect? The voltage divider should still divide all voltages by the same amount, so the output should just be a scaled down copy of the input. Assignments are due 48 hours after the end of lab [[https://canvas.uchicago.edu/courses/64033/assignments/765090|Use this link to submit your report]] This page is adapted from //"Flexible Resources for Analog Electronics"// by Stetzer and Van De Bogart