Quiz: Interactive Controls — Inputs & Concurrency
Test your understanding of reading buttons and knobs, and using their values to change what a robot face does.
1. With button = Pin(14, Pin.IN, Pin.PULL_UP), what does button.value() return when the button is not being pressed?
- 1, because the pull-up holds the pin at 3.3 volts
- 0, because no current is flowing through the button
- A floating value that flickers between 0 and 1
- 65535, the maximum value the pin can report
Show Answer
The correct answer is A. The internal pull-up resistor holds the pin HIGH at rest, so a released button reads 1. Pressing it connects the pin to ground and .value() immediately returns 0. Option C describes what happens without a pull-up — the exact floating-pin problem Chapter 1 introduced.
Concept Tested: Digital Input Reading
2. Why does the polling loop compare current_button_state == 0 and last_button_state == 1 instead of just checking for 0?
- Because
.value()sometimes returns values other than 0 and 1 - Because the comparison compensates for the pull-up resistor's delay
- Because it detects the moment a press begins, turning a held button into one event instead of hundreds
- Because the previous state must be saved before the frame buffer can be cleared
Show Answer
The correct answer is C. A button held down for half a second would read 0 on every pass through a fast loop. Comparing against the previous pass isolates the HIGH-to-LOW edge, so handle_button_press() fires exactly once per physical press rather than repeatedly while the button is down.
Concept Tested: Polling Input Loop
3. What can a polling input loop miss that a button interrupt handler cannot?
- A button that is held down for several seconds
- A press that starts and finishes entirely between two passes through the loop
- A press that occurs while the potentiometer is also being turned
- Any press at all, since polling only reads the pin once at startup
Show Answer
The correct answer is B. Polling only notices a change on its next check, so a very brief press falling in the gap between two checks vanishes without a trace. An interrupt fires on the exact edge regardless of what the main loop is doing. A loop busy with slow drawing work checks even less often, widening that gap.
Concept Tested: Button Interrupt Handler
4. Why should an interrupt handler never call draw_face() or fb.show() directly?
- Because interrupt handlers cannot access global variables like the frame buffer
- Because
Pin.irq()only permits handlers that take no arguments - Because drawing from an interrupt corrupts the frame buffer's byte alignment
- Because a handler can fire mid-loop, and slow work inside it blocks everything else — the same problem a long
sleep()caused
Show Answer
The correct answer is D. The handler should set a flag and return immediately, leaving the main loop to do the real work when it is ready. Handlers can access globals with a global declaration, and Pin.irq() passes the pin object as an argument, so options A and B are both incorrect.
Concept Tested: Button Interrupt Handler
5. Using map_range(value, 0, 65535, -30, 30), what eyebrow angle does a raw ADC reading of 16384 produce?
- About -15 degrees
- About 15 degrees
- About 0 degrees
- About -30 degrees
Show Answer
The correct answer is A. A reading of 16384 sits at about one quarter of the 0–65535 input range. Applying that same fraction to the 60-degree output span gives 15, which added to out_min of −30 yields −15. A reading at the exact midpoint would map to 0, and a reading of 0 would map to −30.
Concept Tested: Potentiometer Value Mapping
6. What does pot.read_u16() return, and what does the ADC actually do?
- A voltage in volts, measured directly by the processor
- Either 0 or 1, since all GPIO readings are digital
- A number from 0 to 65535, produced by hardware that converts an analog voltage into a discrete digital value
- A percentage from 0 to 100 representing the knob's travel
Show Answer
The correct answer is C. The processor cannot compute with a raw voltage — it needs numbers. The analog-to-digital converter measures the incoming voltage and reports it across a 16-bit range, where 0 corresponds to 0 volts and 65535 to 3.3 volts. That raw number then needs mapping before it is useful as a face parameter.
Concept Tested: Analog-To-Digital Conversion
7. What makes Pin.irq() the book's first example of event-driven programming?
- It is the first function that requires importing the
machinemodule - It is the first code that reads hardware rather than drawing to a display
- It is the first pattern that uses a global variable inside a function
- Its handler can run between any two lines of the main loop, rather than in one fixed sequence
Show Answer
The correct answer is D. Every program up through Chapter 12 was sequential: one line always following the line before it. An interrupt breaks that — the handler runs at a moment the programmer does not control. Browsers, phone apps, and games work this same way, so recognizing the pattern here helps you spot it elsewhere.
Concept Tested: Event-Driven Programming
8. In the chapter's three-mode cycle, what happens when the button is pressed while current_mode is GAZE_MODE?
- The mode returns to
NEUTRAL_MODE - The mode advances to
ADJUST_MODE, where the potentiometer begins driving the eyebrow angle - The mode stays at
GAZE_MODEuntil the button is released - Both
GAZE_MODEandADJUST_MODEbecome active at once
Show Answer
The correct answer is B. A single short press always advances one step in the fixed cycle: NEUTRAL to GAZE to ADJUST and back to NEUTRAL. The global state variable stores exactly one value at a time, so option D is impossible by design — never more than one mode is active.
Concept Tested: Mode State Machine
9. What is the main benefit of assigning input polling to the RP2040's second core, and what is the cost?
- Benefit: the display refreshes twice as fast. Cost: the frame buffer needs twice the memory
- Benefit: interrupts become unnecessary. Cost: the potentiometer can no longer be read
- Benefit: a slow drawing task on one core can no longer delay button checks on the other. Cost: both cores may touch the same global state at once, which needs care
- Benefit: MicroPython automatically prevents any conflict between the cores. Cost: only one button may be connected
Show Answer
The correct answer is C. Independent cores mean a complicated draw call cannot make input checking late. The word "cooperative" refers to the fact that safety comes from writing each core's job carefully — MicroPython does not enforce it, so shared variables like current_mode must be touched in predictable, limited ways.
Concept Tested: Dual-Core Processing
10. A project needs to catch a very brief button tap even while the face is mid-redraw. Which approach fits, and what extra work does it require?
- An interrupt handler, which must be kept short and needs debouncing to stop one press firing it several times
- A polling loop with a shorter check interval, which needs no additional handling
- A
sleep()-paced loop, which guarantees the button is read at fixed times - Dual-core processing, which removes any need to detect edges at all
Show Answer
The correct answer is A. An interrupt fires on the exact edge regardless of what the main loop is doing, which is what a brief tap during a slow redraw requires. The cost is complexity: the handler must do almost nothing but set a flag, and real mechanical contacts bounce for a few milliseconds, so a second trigger arriving right after the first must be ignored.
Concept Tested: Button Interrupt Handler