Aerospace Electronics Basics

Cheatsheet Content

### Course Overview: Basics of Electronics for Aerospace Engineers This cheatsheet summarizes key concepts from the course "Basics of Electronics for Aerospace Engineers" by Dr. Tony Jose. #### Learning Outcomes - **Competency:** Use electronic components to design application circuits for aerospace applications. - **Course Outcomes:** - **CO1:** Evaluate electronic components and technologies for aerospace applications. - **CO2:** Determine suitable DC, AC, and brushless DC motors for aerospace systems. - **CO3:** Evaluate analog and digital circuits for aerospace electronics. - **CO4:** Determine the role of altimeters and accelerometers in aircraft/spacecraft automation. - **CO5:** Evaluate the evolution of wireless communication for aerospace applications. ### Why Aerospace Engineers Care About Electronics Electronics are the "nervous system" of aerospace systems, crucial for control and reliability. - **Sensors:** Convert physical parameters into data. - **Controllers:** Make decisions based on sensor data. - **Actuators (motors/servos):** Translate decisions into motion. - **Power System:** Supplies energy to all components. - **EMI/Noise:** Can degrade system performance. **Mini Examples:** UAV flight controllers, Electronic Speed Controllers (ESCs), avionics buses, sensor boards. ### Circuits, Conductors & Insulators #### Electric Circuit A complete closed loop through which electric current flows. - **Needs:** Power source, conducting path (wire), load, switch. - **Break in circuit:** No current flow. #### Material Types | Type | What It Does | Examples | |-------------|--------------------------------|----------------------------------------| | Conductor | Allows current to flow easily | Copper, Aluminum, Water (impure) | | Insulator | Blocks current flow | Rubber, Plastic, Wood, Air | ### Understanding Voltage and Current #### Voltage (V) - **Definition:** Electrical "push" or "pressure" that makes electric charges move. - **Analogy:** Water pressure in a tank. Tall tank = more pressure. - Exists even if no current flows (e.g., wall socket before plugging in). #### Current (I) - **Definition:** The actual movement of electric charges through a conductor. - **Analogy:** Flow of water through a pipe. Wide pipe = more flow. - Only flows when there is a complete (closed) path. ### Electrical Power (P) - **Definition:** Rate at which electrical energy is used or delivered. - **Formula:** $P = V \times I$ - $V$ = Voltage (Volts) - $I$ = Current (Amperes) - $P$ = Power (Watts) - **Impact:** Higher power means more heating and faster battery drain. Explains why resistors burn, wires warm, and batteries deplete quickly under load. - **Example:** If $V = 10 V$ and $I = 0.2 A$, then $P = 2 W$. ### Open Circuit & Closed Circuit #### Open Circuit - **Path:** Broken (e.g., switch open). - **Current:** $0 A$. - **Voltage:** Source voltage appears across the open gap. #### Closed Circuit - **Path:** Complete (e.g., switch closed). - **Current:** Flows according to Ohm's Law ($I = V/R$). - **Voltage:** Source voltage is divided across components in the loop. ### Measuring Voltage and Current #### Measuring Voltage - Measured **across** two points (in **parallel**). #### Measuring Current - Measured **through** the circuit (in **series**). ### Direct Current (DC) - **Flow:** Unidirectional flow of charge. - **Source:** Batteries, solar cells. - **Voltage:** Stays constant with time. - **Uses:** Electronics (TVs, laptops, mobile chargers), battery-powered devices, control systems (PLCs, sensors, actuators) for precision and stability. ### Alternating Current (AC) - **Flow:** Current changes direction periodically. - **Waveform:** Sine wave (e.g., 50Hz in India). - **Voltage:** Alternates between positive and negative. - **Uses:** Household power (230V, 50Hz), industry, long-distance power transmission. ### Learning Unit 1: Introduction to Electronic Components #### Objectives - **1a.** Evaluate benefits and challenges of electronic innovations. - **1b.** Identify types of resistors and their applications. - **1c.** Evaluate types of capacitors, focusing on electrolytic. - **1d.** Identify types of inductors and transformers & interpret specs. - **1e.** Evaluate battery specifications (capacity, voltage, discharge rate). ### Why Electronics Matters in Aerospace Electronics serve as the "nervous system" of aerospace systems. - **Sensing:** Pressure, temperature, IMU, altitude. - **Decision:** Flight controller / avionics computer. - **Action:** Motors, servos, actuators. - **Power:** Conversion, regulation, protection. - **Communication:** Telemetry, navigation, data links. **Conclusion:** No electronics = an expensive kite. ### Evolution and Impact of Electronics #### From Sparks to Smart Systems - **Progression:** Vacuum tubes → transistors → integrated circuits → microcontrollers → embedded systems → IoT/AI edge devices. - **Communication:** Radio → satellite → modern wireless. - **Aerospace Impact:** Avionics became lighter, faster, more reliable. #### Why Electronics "Exploded" - **Miniaturization:** Smaller and lighter components. - **Cost Reduction:** Mass production made electronics affordable. - **Reliability Improvement:** More repeatable and robust systems. - **Key Aerospace Benefit:** Weight reduction directly improves payload and range. #### Impact on Industry - **Automation:** PLCs, sensors, motor drives. - **Quality Control:** Instrumentation, data logging. - **Safety Systems:** Monitoring and interlocks. - **Example:** Motor controllers offer smoother control than mechanical systems. #### Impact on Society - Smartphones, computers, medical devices. - Navigation (GPS), digital payments, smart infrastructure. - Data everywhere, raising privacy and security concerns. - **Conclusion:** Electronics changed not just gadgets, but human behavior. #### Impact on Aerospace - Flight control systems, fly-by-wire. - Navigation, guidance, autopilot. - Reliability & redundancy (fail-safe design). - Unmanned systems (UAVs) enabled by light, cheap electronics. ### Resistors #### What a Resistor Does - **Function:** Current controller + voltage divider. - **Applications:** - Limits current (protection, safe operation). - Creates known voltage drops (sensor interfacing). - Stabilizes digital inputs (pull-up/pull-down). - **Aerospace Examples:** Sensor voltage dividers, LED status indicators, signal conditioning networks. #### Where Resistors Appear in UAV/Avionics - Sensor boards (thermistors + dividers). - Communication lines (termination, pull-ups). - Power protection (inrush limiting). - Feedback networks in regulators. #### Key Specifications - **Resistance Value:** ($\Omega$) - **Tolerance:** (%) - how close to exact value. - **Power Rating:** (W) - how much heat it can safely handle. - **Optional:** Temperature coefficient. #### Types of Resistors - **Fixed:** Carbon film, metal film, wirewound, SMD chip. - **Variable:** Potentiometer, trimmer. - **Special:** Thermistor (NTC/PTC), LDR (photoresistor), Varistor (MOV). #### When to Use Which (Simple Guide) - **Metal Film:** Accurate, low noise (for signals/sensors). - **Carbon Film:** Cheap, general purpose. - **Wire Wound:** High power applications (heating, loads). - **SMD:** Compact, for modern boards. - **Thermistor/LDR:** Sensing applications. - **MOV:** Surge protection. #### Resistor Color Code (Refer to external resources for color code chart) #### Series Circuits - **Current:** Same through all components. - **Voltage:** Divided across components. - **Equivalent Resistance:** $R_{eq} = R_1 + R_2 + R_3 + ...$ - **Failure:** One break = entire circuit fails. #### Parallel Circuits - **Voltage:** Same across all branches. - **Current:** Divided among branches. - **Equivalent Resistance:** $1/R_{eq} = 1/R_1 + 1/R_2 + ...$ - **Failure:** If one branch fails, others keep working. #### Series-Parallel Combinations (Requires circuit analysis to find voltage/current for each component) ### Capacitors #### What a Capacitor Does - Stores energy (temporarily). - Smooths voltage ripple/noise. - Helps during sudden load changes. #### Capacitor Specs That Matter - **Capacitance:** (F, µF, nF, pF) - **Voltage Rating:** (V) - **Tolerance:** (%) #### Types of Capacitors - **Non-polar:** Ceramic (MLCC), Film, Mica. - **Polar:** Electrolytic (aluminum), Tantalum (compact but sensitive). - **Supercapacitors:** Very high capacitance, for backup energy. #### Where Each Type is Used - **Ceramic:** High-frequency decoupling near ICs. - **Film:** Stable, low loss (filters, timing, power applications). - **Electrolytic:** Bulk energy storage/smoothing on power lines. - **Tantalum:** Compact bulk, requires careful handling. - **Supercap:** Short backup, burst power. #### Electrolytic Capacitor: Identify & Safety - **Marking:** Value + voltage (e.g., 100 µF / 25 V). - **Polarity:** Negative stripe on body. - **Safety Rule:** Choose voltage rating above circuit voltage. - **Warning:** Reverse polarity can cause heating/failure. #### Series vs Parallel: Capacitors - **Capacitors in Parallel:** - Total capacitance increases: $C_{eq} = C_1 + C_2 + ...$ - Same voltage across each. - **Capacitors in Series:** - Total capacitance decreases: $1/C_{eq} = 1/C_1 + 1/C_2 + ...$ - Voltage divides across capacitors. #### Series-Parallel Combinations (Requires circuit analysis to find total capacitance) ### RC Circuits - **Series RC Charging:** When a resistor and capacitor are in series, the capacitor charges over time. - **Time Constant (Tau, $\tau$):** The time required for the capacitor voltage to rise to approximately 63.2% of the supply voltage. $\tau = R \times C$. - **Full Charge:** A capacitor is considered "fully charged" after approximately 5 time constants. ### Inductors and Transformers #### Where They Appear in Aerospace - **DC-DC Converters:** Buck/boost converters in avionics/UAV power distribution. - **EMI Filters:** Reducing noise for sensors/communication. - **Motor Drive/ESC:** Input filtering. - **Isolation Transformers:** In some power systems/test benches. - **Quote:** "If you want clean power, you’ll meet inductors whether you like it or not." #### Inductor: What It Does - **Function:** "Current shock absorber." - Stores energy in a magnetic field. - Opposes sudden changes in current. - Smooths current ripple in switching power supplies. #### Inductor Basics - **Symbol:** L - **Unit:** Henry (H) (usually µH or mH in practical circuits). - **Core Idea:** An inductor "fights" current change, not current itself. #### Types of Inductors - **By Construction:** Air-core, Iron-core, Ferrite-core, Powdered iron core, Toroidal, SMD. #### Inductor Selection Specs - **Inductance (L)** - **Current Rating** - **DC Resistance (DCR):** Indicates loss and heating. - **Tolerance** - **Core Material:** Affects frequency behavior. - **Q Factor:** Efficiency/quality at frequency. #### Series and Parallel: Inductors - **Inductors in Series:** - Total inductance adds: $L_{eq} = L_1 + L_2 + ...$ - **Inductors in Parallel:** - Total inductance decreases: $1/L_{eq} = 1/L_1 + 1/L_2 + ...$ - **Mnemonic:** "Adds in series, reduces in parallel." #### Series-Parallel Combinations (Requires circuit analysis to find total inductance) #### Transformer: What It Does - **Function:** Voltage conversion using magnetic coupling. - **Operation:** Works with AC or changing current (not steady DC). - Can step-up or step-down voltage. - Provides electrical isolation (safety + noise reduction). #### Transformer Types - Step-up / Step-down - Isolation transformer - Autotransformer - Pulse transformer (for signals/pulses) - High-frequency transformer (for SMPS) #### Key Transformer Specifications - **Turns Ratio:** Determines voltage ratio. - **Power Rating:** (VA) - **Frequency Rating:** (e.g., 50/60 Hz vs high-frequency SMPS). - **Efficiency** - **Regulation:** Voltage drop under load. - **Insulation / Isolation Rating** - **Temperature Rise / Thermal Class** #### Turns Ratio - **Formula:** $V_p / V_s = N_p / N_s$ - $V_p$: Primary voltage, $V_s$: Secondary voltage - $N_p$: Primary turns, $N_s$: Secondary turns - **Step-up:** If $N_s > N_p \implies V_s > V_p$ - **Step-down:** If $N_s ### Batteries and Chargers for UAVs #### Why This Matters in UAVs - **Battery = Fuel Tank + Power Plant:** - Determines flight time. - Limits maximum thrust (current capability). - Affects weight, safety, reliability. #### What You Will Be Able to Do - Read a UAV battery label (S, V, mAh, C). - Estimate max current and energy (Wh). - Choose a charger mode (balance / storage). - Solve basic UAV battery problems. #### UAV Power System Overview - **Path:** Battery → PDB/Power module → ESC → BLDC motors. - **Path:** Battery → Regulator (BEC/DC-DC) → Flight controller + sensors. - **Challenge:** Motors cause high current spikes; electronics need stable voltage. #### Battery Basics: Specs You'll See - **Voltage (V)** - **Capacity (Ah / mAh)** - **Energy (Wh)** - **Discharge Rating (C)** - **Internal Resistance (IR)** - **Cycle Life** #### Voltage in UAV Batteries - Cells in series add voltage. - **Li-Po Nominal:** ~3.7 V per cell. - **Li-Po Fully Charged:** ~4.2 V per cell. - **Examples:** - 3S ≈ 11.1 V nominal (12.6 V full) - 4S ≈ 14.8 V nominal (16.8 V full) - 6S ≈ 22.2 V nominal (25.2 V full) #### Capacity (mAh) - **Definition:** "How much charge" is stored. - **Conversion:** 2200 mAh = 2.2 Ah. - **Influence:** Flight time (more = longer), Weight (more = heavier). #### Energy (Wh) - **Definition:** The real "how much battery" number. - **Formula:** $Wh = V \times Ah$ - **Importance:** Better for comparing packs with different voltages. #### Discharge Rating (C Rating) - **Estimates Max Current Capability:** $I_{max} \approx C \times Ah$ - **Example:** 2200 mAh = 2.2 Ah, 30C - $I_{max} \approx 30 \times 2.2 = 66 A$. #### Quick Label Reading Example - **Label:** "4S 2200mAh 30C" - **4S:** Nominal 14.8 V. - **2200mAh:** 2.2 Ah. - **30C:** ~66 A max (approximate). - **Energy:** $\approx 14.8 V \times 2.2 Ah = 32.6 Wh$. #### Chemistry Options - **Lead-acid:** Heavy (not for drones). - **NiMH:** Older tech, lower power density. - **Li-ion:** Higher energy density, lower discharge typically. - **Li-Po:** High discharge, common for multirotors. - **LiFePO4:** Safer, but lower voltage per cell. #### Li-Po vs Li-ion - **Li-Po:** - High discharge → good for multirotors. - Lighter for high power demand. - More sensitive to misuse. - **Li-ion:** - Higher energy density → good for endurance/fixed-wing. - Often lower C rating → not for huge current spikes. #### Why Drones "Drop" Suddenly at 30% Battery - **Reasons:** - Voltage sag under high load (throttle). - One weak cell hits low voltage earlier. - **Takeaway:** Battery percentage isn't always accurate; voltage under load matters more. #### Internal Resistance (IR) - **Definition:** The "hidden resistance" inside the battery. - **Impact:** Higher IR leads to more voltage sag and more heat. - Old packs usually have higher IR. #### Safe Operating Window (Li-Po) - **Per Cell:** - Full: 4.2 V - Nominal: 3.7 V - Avoid deep discharge: Don't linger below ~3.3 V/cell under light load. - **Longevity Rule:** Use only ~80% of capacity for regular flying. #### Charging Basics: What a Charger Must Do - **Li-Po Charging:** Uses CC-CV (Constant Current - Constant Voltage) method. - **Constant Current (CC):** Fills faster. - **Constant Voltage (CV):** Finishes safely at 4.2 V/cell. - Charger must control both current and voltage. #### Why Balance Charging Exists - In multi-cell packs, cells don't stay identical; one cell may overcharge. - **Function:** Monitors each cell via a balance connector and equalizes cells during charging. #### Charger Modes - **Balance Charge:** Normal safe charging for multi-cell packs. - **Storage:** Sets pack to storage voltage (~3.8 V/cell). - **Discharge:** Controlled discharge. - **Fast Charge:** Not recommended for beginners. #### Charge Rate (C-rate for charging) - **Formula:** $I_{charge} = (\text{Charge C}) \times Ah$ - **Recommendation:** 1C charge is generally safe for many packs. - **Example:** 2.2 Ah pack → charge at 2.2 A. #### How to Choose a UAV Battery - **Voltage (S):** To match motors/ESC. - **Capacity (Ah):** Vs. weight target. - **Discharge (C):** To meet max current demand. - **Connector Type + Fit** - **Brand/Quality + Pack Condition:** (IR, swelling). #### Estimating Flight Time - **If Average Power is Known:** $\text{Time} \approx \text{Usable Wh} / \text{Average Power (W)}$ - **Usable Wh (Rule of Thumb):** Use 80% of rated energy for safety/longevity. - $\text{Usable Wh} \approx 0.8 \times (V \times Ah)$ #### Battery Exercises 1. A battery is labeled: "6S 5000 mAh 25C". Find: a. Nominal voltage: $6 \times 3.7 V = 22.2 V$ b. Capacity in Ah: $5000 mAh = 5 Ah$ c. Approx max current: $25 C \times 5 Ah = 125 A$ d. Energy in Wh (nominal): $22.2 V \times 5 Ah = 111 Wh$ 2. A 4S 2200 mAh Li-Po is charged at 1C. Find the recommended charge current. - $1 C \times 2.2 Ah = 2.2 A$ 3. A UAV uses a 4S 3000 mAh pack. Average power during hover is 180 W. Estimate flight time using 80% usable energy. - Nominal Voltage: $4 \times 3.7 V = 14.8 V$ - Capacity: $3000 mAh = 3 Ah$ - Total Energy: $14.8 V \times 3 Ah = 44.4 Wh$ - Usable Energy: $0.8 \times 44.4 Wh = 35.52 Wh$ - Flight Time: $35.52 Wh / 180 W \approx 0.1973 \text{ hours} \approx 11.84 \text{ minutes}$