An electrical circuits lab online, for Circuits 1 without hardware
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This is a set of labs for a first circuits course, often called Circuits 1 or circuit analysis. Students build each circuit on a breadboard in the browser, measure it with a meter or a scope, and change it to hit a target.
The circuit above is the starting point: three 10 k resistors from 5 V to ground, with a multimeter on one tap. Every reading comes from a circuit solver, so the meter shows what the circuit does.
Each lab has a starter and checks. A check can read the voltage of any node, so the class feature grades a design by its numbers.
How to set up a lab
Make a class at /class and read out the six-letter join code. Students join at the same address. Then press Assign work, choose A template, and pick the template the lab names.
Under the assignment, press Checks and add the checks listed with the lab. Type the name exactly as shown, because the name is what a student reads when a check fails. Then press Save the checks.
Press Try it on the starter. On the untouched starter, the checks for the change should fail and the rest should pass. That shows the checks can tell a finished lab from an unfinished one.
Lab 5: Design a divider that gives 2.5 V
Three 10 k resistors, r1, r2 and r3, run from 5 V to ground. The meter reads the lower tap, about 1.67 V.
Change only r3, the bottom resistor, so the lower tap reads 2.5 V.
Work out the value on paper first with the divider formula. Then set it, run it and read the meter.
Write down the new voltage at the upper tap too, and then submit.
The starter is the template called A divider, measured in Assign work. It is also the built-in project at /projects/bench-divider.
Add these 2 checks under Checks:
Check 1: The lower tap reads 2.5 V. The form writes it as: the net at pin 1 on r3 reads 2.5 V, within 0.05 V, at 100 ms.
Check 2: The upper tap reads 3.75 V. The form writes it as: the net at pin 1 on r2 reads 3.75 V, within 0.05 V, at 100 ms.
Lab 6: Put a resistor in parallel and predict the change
Start from the same three 10 k resistors.
Add a fourth 10 k resistor across r3, so the two are in parallel. Two equal resistors in parallel act like one of half the value.
Predict both tap voltages before you run it. Then run it and read the meter at each tap.
The starter is the template called A divider, measured in Assign work. It is also the built-in project at /projects/bench-divider.
Add these 2 checks under Checks:
Check 1: The lower tap reads 1.0 V. The form writes it as: the net at pin 1 on r3 reads 1 V, within 0.05 V, at 100 ms.
Check 2: The upper tap reads 3.0 V. The form writes it as: the net at pin 1 on r2 reads 3 V, within 0.05 V, at 100 ms.
Lab 7: Set the blink rate of a 555
A 555 timer runs as an astable, with no microcontroller. Its timing capacitor C1 is 10 µF, and the output makes one cycle about every 0.72 seconds.
Change only C1 so the LED blinks about twice as fast.
Use the 555 formula to pick a value first. Then run it and time the blinks.
The starter is the template called 555 blinker in Assign work. It is also the built-in project at /projects/ne555-blinker.
Add these check under Checks:
Check 1: The 555 output makes one cycle about every 360 ms. The form writes it as: pin OUT on u1 toggles every 360 ms, within 40 ms, watched for 6 s.
Lab 8: Measure an RC time constant
The RC time constant page runs a square wave into 10 k and 100 nF. The time constant is 1 millisecond. Students read the 63 percent point off the scope and compare it with R times C.
This one is measured, not graded by a check. Ask students to write their reading in a sticky note on the canvas and submit.
What to ask for in the write-up
Ask each student to predict the answer on paper first, then build the circuit and measure it. The gap between the two numbers is where the learning happens.
For each lab, the write-up can be short: the target, the part values they chose, the reading from the meter or the scope, and one sentence on why the reading is a little different from the math. The meter’s own input resistance, rounding in the part values and the time it takes a capacitor to settle are all good answers.
Because the circuit is saved with the hand-in, you can open it and see exactly what they built.
When you need SPICE
The editor can run a SPICE netlist too. It does operating point, transient, AC, DC sweeps, transfer function and noise analyses. Its engine is checked against ngspice on 42 benchmark circuits.
It does not run BSIM transistor models, XSPICE devices or distortion analysis. For those, LTspice or ngspice go further.
Questions
Do the checks accept any correct answer?
They accept any circuit that measures right. In Lab 5, a check reads both tap voltages, so only the right value for r3 passes both.
Does the meter load the circuit?
Yes. The meter has 10 megohms of input resistance, like a real one. On the divider it reads 1.666 V instead of 1.667 V, which is a good thing to discuss.
Does this replace a real lab bench?
No. Students should still hold a resistor and use a real meter. The simulator lets them arrive at the bench knowing what to expect.
Will it run on our computers?
Yes. It runs in the browser on laptops, lab PCs and Chromebooks. The simulation runs on each student’s own machine.
Keep going
Build this for real
Open the editor, change a value and watch the number move with it. Nothing to install, and no account needed.