Unit 4: Programming NodeMCU for PWM - Practice Quiz

1 Which technique is commonly used to control the brightness of an LED with a NodeMCU?

2 What happens when the PWM duty cycle of an LED is increased?

3 What does a PWM duty cycle represent?

4 Which duty cycle generally produces the dimmest LED in a PWM circuit?

5 Which duty cycle generally produces the brightest LED in a PWM circuit?

6 Why can an LED appear to glow steadily when controlled by PWM?

7 What component is commonly used to limit current through an LED?

8 What type of motor is commonly positioned using PWM control?

9 What does the pulse width usually determine in a hobby servo motor?

10 Which signal feature is most important for selecting a servo angle?

11 A typical hobby servo can commonly rotate through which range?

12 Which part of a servo motor provides feedback about its shaft position?

13 What is the main purpose of the PWM signal sent to a servo?

14 Which connection is usually required for a servo motor to operate?

15 What may happen if a servo motor does not receive enough power?

16 What does PWM control in a DC motor?

17 What is the effect of increasing the PWM duty cycle on a DC motor?

18 Which component is commonly used to drive a DC motor from a NodeMCU?

19 Why should a DC motor usually not be connected directly to a NodeMCU pin?

20 Which device can be used to reverse the direction of a DC motor?

21 On an ESP8266-based NodeMCU using the default analogWrite() range of 0 to 1023, which value most closely produces 75% LED brightness by duty cycle?

22 An LED connected to a NodeMCU PWM pin appears dim even when analogWrite(pin, 1023) is used. Which hardware issue is the most likely cause?

23 A NodeMCU drives an active-low LED, so the LED turns on when the GPIO output is low. Which PWM value gives approximately 25% visible on-time with a range of 0 to 1023?

24 An LED fade loop increases the PWM value by 20 every 10 ms, starting at 0 and stopping near 1000. Approximately how long does one fade-in take?

25 Two LEDs are driven with the same PWM duty cycle, but one uses a 220 resistor and the other a 1 k resistor. Assuming identical LEDs, what is the expected result?

26 A dimmable LED visibly flickers when PWM is generated by a slow software loop. Which change most directly reduces the flicker while preserving the intended brightness?

27 A program maps an 8-bit brightness command from 0 to 255 into the NodeMCU PWM range 0 to 1023. Which expression provides the most appropriate linear mapping?

28 A standard servo expects a 20 ms PWM period. What frequency should the NodeMCU generate?

29 A servo uses pulse widths from 1.0 ms at 0 degrees to 2.0 ms at 180 degrees. Which pulse width should approximately command 90 degrees?

30 At 50 Hz, what duty cycle corresponds to a 2 ms servo control pulse?

31 A servo jitters and the NodeMCU sometimes resets when the servo starts moving. Which modification is most appropriate?

32 A linear servo mapping uses 1 ms for 0 degrees and 2 ms for 180 degrees. What pulse width should be used for 45 degrees?

33 A servo holds the correct angle but continuously buzzes under load. Which explanation is most likely?

34 A program sends valid servo pulses but then blocks for 500 ms before generating the next pulse in software. What behavior is most likely?

35 A NodeMCU must control the speed of a 6 V DC motor that draws 500 mA. Why should the motor not be connected directly to a GPIO pin?

36 A DC motor is driven through a MOSFET at a 40% PWM duty cycle from a 9 V supply. Ignoring losses, what average motor voltage does this approximate?

37 What is the main purpose of a flyback diode connected across a DC motor controlled by a transistor?

38 A motor does not start at 15% PWM duty cycle but runs after briefly applying 60%. What is the best control strategy for reliable low-speed startup?

39 A single low-side MOSFET provides PWM speed control for a DC motor. What additional circuit is required to control both forward and reverse rotation?

40 A NodeMCU and an external motor driver use separate power supplies, but the PWM input behaves unpredictably. Which connection is most likely missing?

41 An LED is driven from an ESP8266 PWM pin through a resistor. The application uses a 12-bit brightness value from 0 to 4095, while analogWriteRange(1023) is active. Which conversion preserves the intended brightness ratio most accurately?

42 A status LED must appear equally bright at PWM codes 100 and 200 when controlled by a slider, but the second code currently looks much brighter. Which change best addresses the perceptual mismatch while retaining 10-bit PWM resolution?

43 An LED is connected from 3.3 V through a resistor to an NPN transistor collector, with the emitter at ground. The transistor is driven by an active-high PWM signal. Which software behavior produces maximum LED brightness when the circuit is operating correctly?

44 A 3.3 V GPIO drives an LED whose forward voltage is 2.0 V at 10 mA. Ignoring transistor losses, what resistor value is closest to the required average-current limit when the LED is continuously on?

45 A camera records visible LED flicker even though the LED appears steady to the eye. Which modification is most appropriate if the ESP8266 and LED switching hardware can support it?

46 A firmware update changes analogWriteRange() from 1023 to 255, but the application still sends values up to 1023. What is the most likely result for values above 255?

47 Two PWM-controlled LEDs share the same ESP8266 supply. At high duty cycles, both become dimmer and Wi-Fi resets occur. Which hardware change most directly addresses the underlying power problem?

48 A standard servo expects a 50 Hz frame and a 1.0 ms to 2.0 ms control pulse. With a 10-bit PWM range of 0 to 1023, which duty-count interval most closely represents the servo's usable command range?

49 A servo is commanded to 90 degrees using a 1.5 ms pulse, but it moves to an endpoint. The measured frame period is 20 ms and the pulse is actually 15 ms. Which diagnosis is most likely?

50 A servo is powered from a separate 5 V supply, while its signal is generated by the NodeMCU. The servo responds erratically. Which wiring correction is essential?

51 A servo accepts pulses from 0.5 ms to 2.5 ms, but the mechanical linkage safely permits only 20 degrees to 160 degrees. Which control strategy best prevents damaging commands?

52 A servo's neutral position changes after replacing its power adapter, although the PWM pulse width is unchanged. Which explanation is most technically plausible?

53 A servo library and an LED PWM channel are enabled together, and the LED periodically changes brightness whenever the servo moves. What is the best corrective design choice?

54 A servo command is updated every 1 ms with a new pulse width, but the motor jitters badly near its target. Which software improvement is most appropriate?

55 A NodeMCU pin is connected directly to a 250 mA DC motor. The firmware sets 50 percent PWM, but the motor does not start and the board resets. What is the primary design error?

56 A low-side N-channel MOSFET switches a brushed DC motor from a 12 V supply. Which protection arrangement is correct for suppressing the motor's inductive turn-off transient?

57 A DC motor stalls at low duty cycles but runs once manually spun. Which firmware change can improve starting without increasing the steady-state commanded speed excessively?

58 A motor driver uses an H-bridge. The firmware changes direction while the PWM enable remains high, causing a large current spike. Which control sequence is safest?

59 A motor's speed drops under load even though the PWM duty cycle is unchanged. Which conclusion and improvement are most appropriate for a speed-regulated system?

60 A motor driver datasheet specifies a minimum PWM frequency of 20 kHz for inaudible operation, while the selected driver has a maximum switching frequency of 30 kHz. Which setting is valid?