TL;DR: SimCast lessons are step-by-step animated circuit tutorials inside DigiSim. Each step adds components, draws wires, and updates values while a narrator explains in your chosen language. You pause anywhere, replay any step, and finish with a working circuit on your own canvas. Free tier includes a starter set; paid tiers unlock the full curriculum, organized into themed SimCast Sets.
The hardest part of learning digital logic isn’t the gates themselves — it’s wiring them up correctly the first time. Diagrams in textbooks don’t show how a circuit gets built, just the finished schematic. Video tutorials show construction, but you can’t pause and edit the actual wires.
SimCast bridges that gap. It plays a circuit construction back as an animation that runs inside the simulator, on your canvas, while a narrator walks through the reasoning. You can stop at any step, mess with the partially-built circuit, and resume — or scrap the lesson and continue with what you’ve built.
This guide explains what a SimCast lesson is, how to use one, what the SimCast Sets are, and how to fit them into self-study, classroom, and flipped-classroom workflows.
What does a SimCast lesson look like?
When you open a SimCast lesson at https://digisim.io/circuits/simcast/<slug>, the canvas loads empty. The lesson player appears — a panel with playback controls and a step indicator like “Step 3 of 12.”
You press play. The player narrates the first step: a sentence or two of text on screen, with optional voice-over. As the narrator speaks, components animate onto the canvas — an AND gate slides in, a wire draws itself from input switch to gate, the gate’s output light blinks once when the simulation runs.
When the step finishes, the player pauses. You can replay the step, advance to the next one, or skip forward. The canvas state at the end of step 3 is exactly the canvas state at the start of step 4 — a real, runnable, partial circuit.
By the end of the lesson, the canvas holds a finished circuit you built (or rather, watched be built) end to end. You can save it, modify it, share it, or use it as the starting point for an exercise.
How a step actually works
Each step in a SimCast lesson is a small, focused action:
- Component placement. A new gate, switch, light, flip-flop, or other component animates onto the canvas at a specific position.
- Wire drawing. A wire is drawn between two pins, with the path animated so you can follow which pin connects to which.
- Value setting. A switch flips, a clock turns on, a property changes (a register’s bit width, a clock’s period).
- Simulation run. The simulation advances a few ticks so you can see the new piece of circuit in action.
- Narration. Throughout, a narrator (text, voice, or both) explains why this step happens. Not “we’re placing an AND gate” but “we need an AND gate here because both signals must be high before the clock fires.”
The lesson is therefore both a construction guide and a textbook. You see what gets built, when it gets built, and the reason it gets built that way.
Seven languages, same lesson
Every SimCast lesson supports the seven DigiSim languages: English, Chinese (Simplified), Japanese, Spanish, Korean, German, and French. Switching language updates the on-screen text and the voice narration in the same step — the geometry of the circuit doesn’t change, but the explanation does.
This matters most in classroom settings. A teacher running a Spanish-language section can assign the same SimCast lesson as a colleague running an English-language section, and both groups end up at the same finished circuit. The lesson is the same artifact across languages.
It also matters for self-study learners whose first language isn’t English. Watching a tutorial in your native language while the canvas plays back the construction is dramatically more accessible than reading a translated text alone.
Pause, step, replay — the controls
The lesson player exposes four controls:
- Play / pause. Starts or stops the current step’s animation and narration.
- Next step. Skips to the start of the next step, regardless of whether the current one finished.
- Previous step. Rewinds to the start of the previous step. The canvas is restored to its state at that point — components placed in skipped steps disappear.
- Replay step. Plays the current step from its beginning. Useful when you missed a connection or want to hear the explanation again.
You also have full canvas access between steps. After step 5, you can pan, zoom, click on a component to inspect its properties, or even toggle a switch to see how the partial circuit responds. When you press next, the lesson resumes from a clean state for step 6 — your interim experiments don’t leak into the final result.
This is the single biggest advantage over video. A YouTube tutorial of a circuit being built lets you watch. A SimCast lesson lets you watch and poke at the half-built version.
Free tier vs paid tiers
The free tier includes a starter set of SimCast lessons — enough to learn the basics of gates, latches, and simple combinational circuits. Anyone with a DigiSim account can play them with no further commitment.
Paid tiers unlock progressively more advanced sets:
- Fundamental. Adds the full Combinational Circuits set, more practice exercises on basic gates, and the foundational Sequential Logic lessons.
- Professional. Adds the complete Sequential Logic set (registers, counters, state machines), Memory and Storage lessons, and the start of the CPU Architecture path.
- Max. Adds advanced CPU Architecture lessons, ALU design, microarchitecture, and pipelining.
Each tier is a one-time purchase, not a subscription. Once you own a tier, the lessons stay unlocked. The pricing pages list the current set of lessons in each tier; new lessons are added regularly and existing tier purchases include those updates.
What is a SimCast Set?
A SimCast Set is a themed bundle of lessons that share a learning goal. Sets group lessons in a deliberate order so you can work through one topic from foundations to mastery without hopping between unrelated tutorials.
Representative sets include:
- Digital Logic Foundations. AND, OR, NOT, NAND, NOR, XOR, truth tables, simple combinational circuits. The starting point for anyone new to the field.
- Combinational Circuits. Half adders, full adders, ripple-carry adders, multiplexers, decoders, encoders, comparators. Builds toward circuits that compute without memory.
- Sequential Logic. Latches, flip-flops (D, JK, T), registers, counters, shift registers, simple state machines. Adds memory and timing to the toolkit.
- CPU Architecture. ALU, register file, instruction decoder, control unit, the fetch-decode-execute cycle. Pulls everything together into a working processor.
Each set has a detail page at https://digisim.io/circuits/simcast — the lessons hub — where you can browse sets, see how many lessons each contains, and start at any lesson within. There’s also a marketing-side overview at https://digisim.io/simcast covering the curriculum at a higher level.
Three ways to actually use SimCast
1. Self-study
Pick a topic you want to learn. Open the lessons hub at /circuits/simcast, find the SimCast Set that covers it, and start at lesson one.
Work through each lesson at your own pace. Pause when you want to think, replay when you want to confirm, and run the partial circuit between steps to convince yourself it really does what the narrator says it does.
A good self-study sanity check: at the end of each lesson, close the lesson player, clear the canvas, and try to rebuild the same circuit from memory. If you can, you’ve internalized the construction. If you can’t, replay the lesson focusing on the parts you forgot.
For an even more guided self-study path, the upcoming digital logic roadmap from gates to CPU in 30 days will sequence SimCast Sets into a daily plan.
2. Classroom (synchronous)
A teacher projects the SimCast lesson on a classroom screen. Students follow along on their own machines, either watching the projected version or running the lesson independently in their browser.
The teacher pauses at moments worth discussing — “before I press next, what do you predict will happen here?” Students answer, the teacher advances, and the canvas confirms or corrects the prediction.
Because every student ends up with the same finished circuit on their own canvas, the teacher can immediately assign a follow-up exercise: “modify this counter to count by two.” No setup, no copy-paste — students start from the canvas the lesson left them.
For grading the resulting submissions, see grading circuits in seconds: the DigiSim workflow.
3. Flipped classroom
Assign a SimCast lesson as homework before class. Students watch it, build the circuit alongside the lesson, and arrive in class already familiar with the construction.
Class time then becomes the deeper conversation: why did we choose a JK flip-flop over a D flip-flop here? What changes if we replace the asynchronous reset with a synchronous one? Without the flipped model, those discussions get squeezed by the time it takes to physically build the circuit. With it, the building is already done.
A natural pairing: assign the D flip-flop SimCast lesson as homework, then in class compare its waveforms to a master-slave JK using a scope. (For the scope side of that exercise, see the post on using the oscilloscope to debug digital circuits.)
Why step-through beats video
Three structural reasons SimCast outperforms a screen-recorded YouTube tutorial:
- Interaction at any step. Pause a YouTube video and you have a frozen image. Pause a SimCast lesson and you have a runnable partial circuit. The difference compounds across a 12-step lesson.
- No editing artifacts. Video tutorials cut, jump, fast-forward, and zoom. SimCast plays at one speed in one frame. There’s nothing to lose track of.
- Saved as a real circuit. When the lesson ends, the result is a circuit on your canvas — you can save it, share it, embed it, or use it as a starting point for the next lesson. A YouTube tutorial leaves you with notes you have to recreate manually.
This is the same case for browser-native simulation that we made in the end of the breadboard: why virtual labs are here to stay, applied to instruction rather than experimentation.
How to start in five minutes
If you’ve never opened a SimCast lesson, here’s the shortest path:
- Sign in to DigiSim. (Anonymous browsing works for some lessons, but signing in lets the player remember your progress.)
- Go to the lessons hub at
/circuits/simcast. - Pick the Digital Logic Foundations set, choose lesson one (typically an introduction to AND/OR/NOT gates), and press play.
- Let it run end-to-end the first time without pausing. Just watch what gets built and listen to the narration.
- Replay it. This time pause at each step, predict what’s coming next, then advance.
By the end of two passes through a single lesson, you’ll have an instinct for the rhythm of the format. After that, picking up new SimCast lessons is fast.
For a broader first-day tour of the simulator itself, your first 5 minutes with DigiSim.io: a beginner’s journey covers the canvas controls and component palette without the lesson layer on top.
When SimCast is and isn’t the right tool
SimCast is the right tool when:
- You want to learn how a specific circuit gets built, step by step.
- You’re preparing a lesson and want a ready-made tutorial to assign.
- You’re stuck on a concept and need to see it constructed slowly with explanation.
It’s not the right tool when:
- You already know how to build the circuit and just want a blank canvas to experiment.
- You need to debug an existing circuit. (For that, see using the oscilloscope to debug digital circuits.)
- You want a reference document to skim. (Use the blog posts and component docs — they’re searchable.)
A natural division of labor: read a blog post for the concept, run a SimCast lesson for the construction, build your own variant on a fresh canvas for mastery.
Where to go next
If you’re brand new to digital logic, start with digital logic 101: your first steps with AND, OR, and NOT gates and then run the matching SimCast lesson in the Digital Logic Foundations set. The reading and the lesson reinforce each other.
If you’re further along and aiming for a real understanding of how a CPU comes together, the upcoming post on building a CPU from scratch in a simulator will use SimCast lessons as the connective tissue between gate-level and architectural views.
Ready to start? Open the SimCast lessons hub and pick your first lesson — the free tier alone is enough to spend an afternoon learning, with no commitment.
