PWM and Signal Fundamentals

What is PWM?

Pulse Width Modulation (PWM): Switching power on/off rapidly to control average power delivery.

100% Duty Cycle (always on):
████████████████████████████████

50% Duty Cycle:
████    ████    ████    ████

25% Duty Cycle:
██      ██      ██      ██

0% Duty Cycle (always off):
________________________________

Key terms:

• Period: Time for one complete on/off cycle
• Frequency: Cycles per second (Hz) = 1/Period
• Duty Cycle: Percentage of time signal is HIGH

$$\text{Duty Cycle}=\frac{T_{on}}{T_{on}+T_{off}}\times 100\mathrm{\%}$$

---

Why PWM in Modern Motorcycles?

Efficiency

• Transistor fully on or fully off (low heat)
• No power wasted in resistors
• Precise control without energy loss

Applications in EURO 5+ Bikes

Component	PWM Purpose
Cooling fan	Variable speed control
Heated grips/seats	Temperature regulation
LED lighting	Brightness control / DRL dimming
Fuel pump	Pressure regulation
Idle Air Control	Idle speed adjustment
EVAP purge valve	Fuel vapor metering
Secondary air valve	Catalyst heating

---

Signal Types in Motorcycles

Every wire that isn't simply carrying power is carrying a signal — information. Signals come in two fundamental flavors, and modern bikes lean heavily on both.

Analog vs Digital: The Big Picture

Aspect	Analog	Digital
Values	Infinite (smooth, continuous)	Two only: HIGH / LOW (1 / 0)
Example	0.5–4.5V from a throttle sensor	0V or 5V on/off state
Carries	A magnitude (how much)	A state, or encoded data (bits)
Noise immunity	Poor — noise corrupts the value	Excellent — only "is it high or low?"
Resolution limit	Wiring & ADC quality	Number of bits
How the ECU reads	ADC (analog-to-digital converter)	Direct logic input / timer

Key idea: The engine's real-world quantities (temperature, pressure, throttle angle) are analog. The ECU's processor is digital. So a sensor is either read through an ADC, or the sensor pre-converts its value into a frequency, pulse count, or duty cycle the ECU can time directly.

Why digital wins for communication: A digital line only has to answer "high or low?", so electrical noise, long harness runs, and voltage sag barely affect it. That robustness is exactly why data buses like CAN and LIN are digital — dozens of modules share a couple of wires reliably. More on that in the Advanced Electronics chapter.

Analog Signals

Continuously variable voltage representing a value.

Examples:

• Throttle Position Sensor (TPS): 0.5V - 4.5V
• Coolant Temperature Sensor: Resistance varies with temp
• Manifold Absolute Pressure (MAP): 0.5V - 4.5V
• Oxygen sensor (narrowband): 0.1V - 0.9V

Testing: DC voltage mode, check at various conditions

Digital Signals

Two states only: HIGH or LOW.

Examples:

• Neutral switch: 0V (in gear) / 12V (neutral)
• Side stand switch: Open/Closed
• Clutch switch: Open/Closed
• Kill switch: Open/Closed

Testing: DC voltage, should see 0V or ~12V only

Frequency/Pulse Signals

Signal that varies in frequency with measured value.

Examples:

• Wheel speed sensors (ABS): Pulses per revolution
• Crankshaft position sensor: Pulses per rotation
• Vehicle Speed Sensor (VSS): Frequency = speed

Testing: Frequency mode on multimeter, or oscilloscope

PWM Signals

Fixed frequency, variable duty cycle.

Examples:

• Injector pulse width
• Cooling fan speed
• Heated grip control

Testing: Duty cycle mode (%) on multimeter, or oscilloscope

Encoding a Value on a Digital Wire

Frequency and duty cycle are how a digital (two-state) line can still carry an analog magnitude — the wire is always fully high or fully low, but how often or how long it stays high represents the value:

Method	What varies	The value is read from	Example
Frequency	Pulses per second (Hz)	Time between edges	Wheel speed, VSS
Duty cycle	HIGH time within a cycle	% of period spent HIGH	Cooling fan, heated grips, fuel pump
Serial	Pattern of bits over time	Decoding the bit stream	CAN / LIN messages

This is the conceptual bridge to later chapters: a sensor often speaks in frequency or duty cycle, while an entire data bus (CAN/LIN) speaks in timed patterns of bits.

---

Sensor Signal Characteristics

Hall Effect Sensors

Output: Clean digital square wave

Used for:

• Crankshaft/camshaft position
• Wheel speed (modern ABS)
• Gear position

Characteristics:

• 3 wires: Power, Ground, Signal
• Output: 0V / 5V (or 0V / 12V)
• Clean edges, easy to read on scope

Variable Reluctance (VR) Sensors

Output: AC sine wave, amplitude varies with speed

Used for:

• Crankshaft position (older systems)
• Wheel speed (older ABS)

Characteristics:

• 2 wires: No power needed
• AC voltage output (can be 0.5V to 100V+)
• Amplitude and frequency increase with speed
• Measure with AC voltage

Resistive Sensors

Output: Variable resistance based on measured condition

Used for:

• Coolant/oil temperature (NTC thermistor)
• Fuel level sender
• Throttle position (older potentiometer type)

Characteristics:

• Usually 2 wires
• ECU provides reference voltage
• Resistance changes → voltage divider changes

---

Introduction to Oscilloscope

Why Oscilloscope?

A multimeter shows average values. An oscilloscope shows signal shape over time.

Multimeter can't show:

• Signal glitches or dropouts
• Waveform shape (sine, square, etc.)
• Timing relationships between signals
• Fast transients

Basic Oscilloscope Concepts

Time base (horizontal): How fast the display sweeps (ms/div) Voltage scale (vertical): Voltage per division (V/div) Trigger: What causes the display to start capturing

Automotive Oscilloscope Uses

Signal	What to Look For
CKP (crankshaft)	Missing tooth pattern, consistent amplitude
CMP (camshaft)	Correct timing relative to CKP
Injector	Sharp on/off transitions, correct pulse width
Ignition primary	Clean dwell, good spark line
Wheel speed	Consistent pulses, no dropouts
O2 sensor	0.1V-0.9V switching, cross-count rate

Recommended Entry Oscilloscopes

Type	Examples	Price
USB PC-based	Hantek 6022BE, PicoScope 2204A	$80-200
Handheld automotive	Micsig, Hantek 2D72	$150-300
Professional	PicoScope 4425A, Fluke 190	$1500+

---

Practical: Testing PWM Fan Circuit

Tools Needed

• Multimeter with duty cycle function
• (Optional) Oscilloscope

Procedure

1. Locate cooling fan connector (2-3 wires)
2. Identify signal wire (often thinner, different color)
3. Set multimeter to duty cycle (%)
4. Back-probe signal wire with meter
5. Start engine, let it warm up
6. Observe duty cycle increase as temp rises

Expected results:

• Cold engine: 0% or low duty cycle
• Normal operating temp: 30-60%
• Hot (fan running hard): 80-100%

---

Practical: Reading Crankshaft Position Signal

Hall Effect Type (3-wire)

1. Identify wires: Power (5V/12V), Ground, Signal
2. Connect oscilloscope to Signal and Ground
3. Set timebase: 10-50ms/div
4. Set voltage: 2-5V/div
5. Crank or run engine
6. Should see clean square wave with missing tooth gap

VR Type (2-wire)

1. Connect oscilloscope across both wires
2. Set to AC coupling
3. Set voltage: 1-5V/div initially
4. Crank engine
5. Should see sine wave with missing tooth signature
6. Amplitude increases with RPM

---

Key Takeaways

1. PWM = efficient power control via rapid switching
2. Duty cycle = percentage of ON time; frequency = cycles per second
3. Analog signals = continuous voltage representing a value (needs an ADC to read)
4. Digital signals = two states only (HIGH/LOW); robust against noise
5. Frequency & duty cycle let a digital wire carry an analog value — the basis for many sensors and for CAN/LIN buses
6. Hall effect = clean digital output, needs power
7. VR sensors = AC output, amplitude varies with speed
8. Oscilloscope shows what multimeters can't: signal shape and timing