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Notes

Power

Ref: Power Electronics Week

Battery

Note: Battery

Ref: Battery University

  1. Battery Types
    • Li-ion: High energy density, lightweight, common in laptops/tools, moderate safety risk
    • LiPo: Light, high output, RC/drones, slightly less safe
    • LiFePO4: Very safe, long life, stable, heavier, lower energy density
  2. Battery Units
    • Voltage (V): Nominal vs full charge voltage (e.g., Li-ion 3.7 V nominal, 4.2 V full)
    • Capacity (Ah / mAh): Energy stored (2 Ah → 2 A for 1 h)
    • Energy (Wh): V × Ah, used for transport limits
      • ≤ 100 Wh: can be carried in hand luggage
      • 100–160 Wh: may require airline approval
      • over 160 Wh: usually not allowed
    • Current (A): Continuous vs peak discharge
  3. Cell Configuration
    • S = Series cells
    • 1 cell: 3.7 V nominal, 4.2 V max, 3.0 V min
    • Example: 3S → 11.1 V nominal (max 12.6 V), 4S → 14.8 V nominal (max 16.8 V)
  4. Connectors
    • DC barrel jack: Common 12 V devices, various sizes (5.5/2.1, 5.5/2.5 mm)
    • JST: Small devices, balance leads, 1–3 A
    • XT30/60/90: RC/robotics, high current (e.g., XT60 → 60 A)
    • T/Deans: Small–medium high-current RC use
    • Balance connectors: Monitor/charge each cell (e.g., 3S → 4 pins)
  5. BMS (Battery management system)
    • BMS: Protects and manages Li-ion batteries.
    • Functions: Overcharge, overdischarge, overcurrent protection; cell balancing.
    • Components: MOSFETs/switches, voltage sensors, balancing circuits, protection IC.
    • How it works: Monitors voltages/current, disconnects load/charger if unsafe, balances cells during charging.
    • Battery types: With BMS (safe, balanced) vs without BMS (raw, higher risk).

HJGHY 12V 6000mAh Li-ion battery

battery

Item Specification Considerations
Type Li-ion with BMS Balance of weight and safety
Capacity 6000 mAh Max: 1.5A x 4 motors x 1 hour... will last longer than that
Cells 3S2P (3 cells in series, 2 cells in parallel) 3 x 3.7 V ≈ 11.1 V nominal, 2 x 3000 mAh ≈ 6000 mAh
Energy 72 Wh ≥100Wh: It can be carried in hand luggage
Dimensions / Weight 38 × 70 × 56 mm / 290g
Input / Output 12.6 V DC / 10.8–12.6 V Voltage drop detection required (when ≤10.8V)
Connector DC jack 5.5 × 2.1 mm
Operating Temp -20 to 60 °C
Life 1000+ cycles

Voltage regulation

While the motor driver can handle 12V, stable 5 V or 3.3 V is needed to power Pico and other input / output devices. Around 500 mA ~ 2 A current is expected.

Note: 5V and 3.3V line

Note: Microcontroller power consumption

  • Pico power consumption: typical 30–100 mA depending on load
  • ESP32-S3 Sense power consumption: Wi-Fi up to ~355mA, camera 20–100mA, on-device processing 10–70mA... Peak current: ~500 mA ~ 1A

  1. Linear regulator

    • LDO = Low-Dropout Linear Regulator → converts higher Vin to stable lower Vout.
    • Simple, low noise, uses transistor and feedback.
    • Converts higher voltage to lower by wasting excess energy as heat.
    • Works when input is slightly above output (Vin ≥ Vout + Vdrop).
    • Efficiency ≈ Vout / Vin.
    • Best for small voltage drops and low noise requirements.
    • Low-Loss Surface Mount Three-Terminal Regulator 3.3V800mA NJM2845DL1-33
      • Output: 3.3V, max. 800mA
      • Input: max. 12.3V
      • Dropout: 180mV
      • Power loss (heat): P = (Vin − Vout) × I
        • I = 0.5A → 0.85W (~42.5°C rise)
        • I = 1A → 1.7W (~85°C rise): needs heat dissipation

  2. Switching regulator (buck converter)

General comparison table of buck converter and LDO (12V → 5V, 2A and 5V → 3.3V, 1A)

Regulation Method Efficiency (typ.) Heat Dissipation Notes / Suitability
12V → 5V, 2A Buck converter ~85–95% ~1–2 W Recommended. Efficient and cool.
LDO ~40% 14 W (7V drop × 2A) Not practical. Too much heat.
5V → 3.3V, 1A Buck converter ~85–95% ~0.2–0.3 W Works well, but usually unnecessary for 1A.
LDO ~66% 1.7 W (1.7V drop × 1A) Acceptable, but warm. Needs good thermal layout.

Pico power

  • Pico operates at 3.3V logic, but its GPIO pins operate at 3.3V.
  • Internal buck-boost regulator converts 1.8–5.5V (VSYS) to a stable 3.3V for the MCU and GPIO.
  • Power options:
    • USB (VBUS) → 5V input, stepped down to 3.3V internally.
    • VSYS pin → Accepts 1.8–5.5V directly.
    • Pico automatically powers from the higher-voltage source (USB or battery) via a Schottky diode (D1), which prevents reverse current between supplies.
  • Monitoring:
    • GPIO24 is used to monitor the existence of VBUS, signaling high if VBUS is present.
    • VSYS is monitored via ADC channel 3 (GPIO29/ADC3), which can be used as a crude battery voltage monitor if a battery is connected to VSYS.
  • For external devices:
    • Use Pico’s 3.3V output (max 300mA) for low-power peripherals.
    • For 5V devices, power them from the 5V line (e.g., VBUS), but use logic level converters if connecting to GPIO.

  • Pinout:

    Pico pinout

    (Image: Pico-series Microcontrollers)

    Pin Name Dir Voltage Description
    40 VBUS In/Out 5V 5V from USB port. Outputs 5V when Pico is USB-powered. Can also be used as 5V input (do not connect if USB is plugged in).
    39 VSYS In 1.8-5.5V Main power input (e.g. battery or external supply). Automatically powered from VBUS when USB is connected.
    38 GND - 0V Common ground.
    37 3V3_EN In - Enables the onboard 3.3V regulator. Low = off, High (default) = on. Pull low to shut down 3.3V rail and Pico.
    36 3V3(OUT) Out 3.3V Output from the internal regulator; use to power external 3.3V devices (max ~300mA).

Measuring battery voltage

Notes

  1. ADC (Analog to Digital Converter)

    • The Pico’s ADC (Analog-to-Digital Converter) converts analog voltages (0–VREF) to 10-bit values (0–1023).
    • ADC_VREF (pin 35) sets the reference voltage—default 3.3V, or an external precise source for better accuracy.
    • For battery monitoring, divide the 12V voltage with resistors so the ADC input ≤ VREF, then scale it to find the actual voltage.

    Pico ADC pins

    Pin Name Dir Description
    35 ADC_VREF In Reference voltage for ADC (default 3.3 V). Can connect an external precise reference for better accuracy.
    34 ADC2 (GP28) In Analog input channel 2 (0–VREF). Used for sensor or voltage measurement.
    33 AGND (GND) - Analog ground. Connect here when using ADC for cleaner measurements.
    32 ADC1 (GP27) In Analog input channel 1.
    31 ADC0 (GP26) In Analog input channel 0 — often used for battery voltage monitoring.

  2. Note: Voltage divider

    • A voltage divider splits voltage using two resistors in series. The input voltage drops proportionally across them.
    • It is like water flowing from a high tank to the ground. Resistors represent flow resistance, voltage is water pressure, and Vout is a tap where pressure is divided according to the resistance ratio.

    Formula: Vout = Vin × (R2 / (R1 + R2))

    Example: Vin = 12V, R1 = 33kΩ, R2 = 10kΩ
    Vout = 12 × (10 / 43) ≈ 2.8V

    divider

    DigiKey | Voltage divider calculator

Safety & stability

Key Points

  1. Primary Protection (Highest priority)
    • Blade Fuse + BMS: Prevents catastrophic power faults at the system level.
  2. Secondary Protection (Intermediate layer)
    • Reverse diode + TVS + Capacitor: Handles transient or user-wiring mistakes.
  3. Tertiary Protection (Module level)
    • PTC fuses and local power filtering: Ensures one faulty module does not destroy others.

Stage Component Function / Protection Typical Placement / Notes
1 Blade Fuse Main short-circuit protection Placed immediately after the battery terminal. 7.5–10 A typical.
2 Reverse Polarity Diode Reverse connection protection Between fuse and power input. Use Schottky type for low voltage drop.
3 TVS Diode Transient voltage suppression In parallel with power line near battery or motor. Select clamp voltage < 20 V.
4 Bulk Capacitor Inrush current absorption / voltage smoothing 100 ~ 470 µF / 25 V ~ typical. Place close to motor driver or power module.
5 Resettable Fuse (PTC) Small line overcurrent protection Used per-module or per-branch to prevent local overload.
6 Power Distribution Routes power to individual modules Divides current to multiple circuits. Use proper wire gauge.

Fuse

  • Fuses protect circuits from overcurrent that could cause wire damage, fire, or component failure.
  • When current exceeds the rated limit, the fuse melts (opens) and stops the flow.
  • Choose a fuse rated slightly above normal current draw (e.g., 1.5× load current).
  • For logic-level (5 V / 3.3 V) sections, fuses are optional or can be replaced with PTC resettable fuses.

  • Necessity (according to ChatGPT)

    Voltage / Current Range Typical Source Fuse Necessity Notes
    >12 V (2 A or more) Battery, motor supply Required High current can cause wiring shorts or fire; main fuse recommended.
    5 – 12 V (under 2 A) Adapter, regulator Optional Add if driving motors or unregulated loads.
    Low current (<1 A, logic level) USB, MCU, sensor lines Not needed Power sources usually current-limited; low risk of damage.

  • Types

    Type How It Works Common Use Key Parameters Typical Ranges
    Glass Tube (Cartridge) Metal wire melts when current exceeds the rating. Power supplies, DC circuits, general protection. Current, voltage, blow speed (fast/slow). 32V–250V, 100 mA–10 A
    Blade (Automotive) Metal strip between blades melts under overload. Battery or motor power lines (12 V). Current, voltage (DC), time delay. 12V–32V, 1 A–40 A
    Resettable (PTC / Polyfuse) Resistance increases sharply when overheated; resets after cooling. USB ports, 5V rails, small electronics. Hold/trip current, voltage, reset time. 6V–60V, 50 mA–5 A
    SMD Fuse Thin conductive film melts under overcurrent. Compact PCBs, embedded systems. Current, voltage, package size. 24V–125V, 50 mA–5 A

  • Examples:

  • Blade fuse: AliExpress | Mini blade fuse & fuse holder for PCB, 32V 15A

Ref:

Diode

  • Diodes act as one-way valves for current - conduct in one direction, block in the other.
  • Every diode has a forward voltage drop (Vf). They’re not lossless, some voltage and power are lost as heat.
  • Types:
    • Silicon diode: standard type, ~0.7 V drop, reliable, general-purpose.
    • Schottky diode: very low Vf (0.15–0.45 V), fast switching, used in power circuit
    • Zener diode: conducts in reverse at a specific voltage, used for voltage regulation/protection
    • LED: emits light, a diode that converts electrical energy to photons

  • For 10A / 12V application:

    Method Wiring Normal Voltage Drop Reverse Polarity Behavior Pros Cons Suitability (12V 10A)
    Series Diode (Schottky / SBR) +12V → Diode → Load 0.3–0.5 V Blocks reverse current Simple, compact Power loss, heat Good if heat managed
    Shunt Diode + Fuse +12V → Fuse → Load; Diode (rev) → GND 0 V Short → blows fuse No loss in normal use Fuse replacement Good for simple protection
    MOSFET Ideal Diode +12V → MOSFET → Load < 0.1 V (Rds × I) Blocks automatically Very low loss, reusable Slightly complex Best overall choice

  • Akiduki | SBR DiodeSBR15U30SP5

    • DC Withstand Voltage: 30V
    • Peak Withstand Voltage: 30V
    • Average Forward Current: 15A

Ref:

TVS diode

  • A TVS diode is a protection component that absorbs sudden voltage spikes (transients)
    • Examples: when motors stop abruptly, when the battery cable is plugged/unplugged
  • How it works:
    • Under normal voltage: TVS diode does nothing (high impedance).
    • When a surge occurs: → Voltage exceeds breakdown voltage → diode clamps voltage by shorting surge to ground momentarily.
  • Akiduki | TVS Diode (Surge Absorber) SMBJ45CA
    • Type: Bidirectional TVS
    • Peak Reverse Operating Voltage: 45V
    • Min. Breakdown Voltage: 50V
    • Max. Breakdown Voltage: 55.3V
    • Max. Power Dissipation: 400W

Capacitor (Ceramic / Electrolytic)

  • Capacitors smooth voltage and absorb noise or spikes from motors, converters, and wiring. Each value works at a different timescale.
  • Charge accumulates on plates... no real current flows “through” a capacitor.
  • General rules:
    • Use one large electrolytic (100–470 µF) near the main power input
    • Add 10 µF + 0.1 µF near each module or IC.
    • Keep leads short and close to the power pins for best effect.

  • Types:

    • Ceramic: Not Polarized, High frequency but lower capacitances
    • Electrolytic: Polarized, higher ESR and therefore suitable for lower frequencies but higher capacitances
    Capacitance Main Role Placement / Application Notes
    0.1µF High-frequency noise removal Between VCC and GND of each IC Ceramic; essential for logic ICs.
    1µF Mid-frequency noise absorption Near ICs or LDO regulators Ceramic; complements 0.1µF for mid-range noise.
    10µF Voltage stabilization On 5V or 3.3V regulator outputs Ceramic or electrolytic; follow regulator datasheet.
    100 ~ 470µF Power line smoothing After DC input (e.g., 12V) Electrolytic; absorbs surges and inrush current.
    • Since the A4988 carrier already has 0.1uF to 4.7uF capacitors, only bulk capacitors need to be added.

Electronic components

SMD & THT

Footprint

  • Footprint means the shape and size of the component on a circuit board (PCB)... where the metal pads go for soldering
  • Footprint codes describe package type, pin spacing, body size, and pin count

  • Essential for matching pad layout to the physical component

  • Resistors & Capacitors (SMD types)

    • The SMD package code (e.g., 1206) indicates the component’s length and width in inches.
      • Example: 1206 → 0.12" × 0.06" ≈ 3.2 × 1.6 mm

    • Common SMD Package Sizes:

      Code (Inch) Dim (mm) Notes (Ease of soldering)
      0201 0.6×0.3 Way too small
      0402 1.0×0.5 Too small
      0603 1.6×0.8 Common but still too small for me
      0805 2.0×1.25 Not impossible
      1206 3.2×1.6 Larger, higher power, Easier to handle
      1210 3.2×2.5 High current
      1812 4.5×3.2 Power circuits

  • Transistors / Diodes (SOT (Small Outline Transistor) packages)

    • Example: SOT95P280X145-5N

      Code Part Meaning Notes
      SOT Small Outline Transistor Surface-mount package family. Used for ICs, regulators, transistors.
      95P 0.95 mm pin pitch Center-to-center spacing between leads.
      280 2.80 mm lead span Distance from one outer lead tip to the opposite side.
      X145 1.45 mm body height Overall thickness of the package.
      5N 5 leads Indicates pin count and variant.

    • Examples:

      Code Meaning Typical Part Example Notes
      SOT-23-3 3-pin Small transistor, diode Very common (e.g. 2N3904 SMD)
      SOT-23-5 5-pin Regulator or op-amp Slightly bigger
      SOT-223 Large flat w/ heat tab Voltage regulator (e.g. AMS1117) Can dissipate heat
      SOT-89 Medium-size transistor Power transistors, regulators Handles more current

  • IC packages (Chips, Drivers, Op-Amps, etc.)

    • Example: SOIC127P600X175-8N

      Code Part Meaning Explanation
      SOIC Package type “Small Outline Integrated Circuit” — a common flat, rectangular IC package with leads on both sides. Other examples: TSSOP, QFN, LQFP.
      127P Pin Pitch (Lead Spacing) 1.27 mm between the centers of adjacent pins. Important for PCB pad spacing.
      600 Body Width The width of the plastic body, here 6.00 mm.
      X175 Body Height (Thickness) 1.75 mm thick (the “X” just separates the numbers).
      -8 Pin Count Total number of leads — here, 8 pins.
      N Variant / Shape suffix Often denotes normal (N) polarity, or sometimes manufacturer variant. (Not always critical for footprint).

    • Examples:

      Code Meaning Pin Pitch Example
      SOIC-8 (1.27P) Small Outline IC 1.27 mm LM358, 555 Timer
      TSSOP-8 (0.65P) Thin Shrink SOIC 0.65 mm Op-amps, EEPROM
      MSOP-8 (0.5P) Mini SOIC 0.5 mm Smaller op-amps
      QFN-32 (0.5P) Quad Flat No-lead 0.5 mm Modern MCUs (e.g. ESP32-C3)
      LQFP-64 (0.5P) Low-profile QFP 0.5 mm ARM MCUs
      DIP-8 / DIP-28 Through-hole 2.54 mm Breadboard-friendly ICs

SMD aluminum electrolytic capacitors

  • Common SMD Electrolytic Capacitor Case Sizes

    Case Code Ø (mm) H (mm) Typical Voltage Range Typical Capacitance Range
    D4×5.4 4 5.4 6.3–16 V 4.7–47 µF
    D5×5.4 5 5.4 6.3–25 V 10–100 µF
    D6.3×5.8 6.3 5.8 6.3–35 V 47–220 µF
    D8×10.5 8 10.5 10–35 V 100–330 µF
    D10×10.5 10 10.5 16–50 V 220–1000 µF
    D10×12.5 10 12.5 25–63 V 330–1000 µF
    D12.5×13.5 12.5 13.5 35–100 V 470–2200 µF

  • D8×10.5 is less than the height of the pin socket; it fits under the A4988 boards

Jumper pin

  • Use by inserting them into pin headers, etc. The inserted pins become conductive.
  • Example: Akiduki | Yellow jumper pin (2.54mm pitch)
  • Appication:
    • The A4988 microstep pins (MS1-3, HIGH or LOW) can be manually switched on the board using jumper pins
    • In this case, they are hardwired to HIGH (5V)

PCB via and rivets

  • Via: a small hole that electrically connects copper traces between PCB layers
  • PCB rivets: Hollow copper sleeves used as a simple DIY way to make vias on double-sided boards to provide a top–bottom connection
  • Typical size: 0.6mm and 1.0mm
  • Typical drill sizes: ~0.8–0.9 mm for 0.6 rivets, ~1.5 mm for 1.0mm ones
  • Rivets must still be soldered after flaring to ensure electrical connection

Alternatives:

  • Wire vias (soldered wires through holes)
  • Manufacturer-plated vias

Ref: PCB rivets

Others

Twisted pair cable

  • Twisted pair reduces EMI (electromagnetic interference) by keeping two conductors close and twisted
  • Common-mode noise cancels because both wires receive the same interference
  • Small loop area + opposing currents greatly reduce radiated and received noise
  • Application examples:
    • Power delivery: twist 5V + GND or 12V + GND to suppress current-loop noise
    • Communication lines: UART over long cables, I2C in noisy environments

Ref: Wikipedia | Twisted pair

Wire diameter

  • Unit: AWG (American Wire Gauge)
    • AWG is a standardized system for wire diameter.
    • Smaller number means: thicker wire, lower resistance, handles more current.
  • For NEMA 17 Stepper Motor
    • Typical phase current: 1-2 A, occasionally up to 3 A.
    • Recommended wire sizes (for ≤1 m cable):
      • AWG 24 → good general choice (up to ~2 A)
      • AWG 22 → safer for higher current or longer wires
    • For longer cables (>1 m): use one size thicker to reduce voltage drop.
  • Digi-Key Wire Size Calculator
    1. In the "AWG" field, enter a wire gauge (e.g., 24).
    2. The calculator shows:
      • Diameter (in mm or inches)
      • Cross-sectional area
      • Resistance per unit length
      • Maximum current estimate
    3. Conversely, enter a diameter or area to find the closest AWG

Programmable I/O

  • Pico allows flexible assignment of UART, I2C, and SPI pins via Programmable I/O.
  • Using GP0/GP1 for UART, GP20/GP21 for I2C is fine, but must be configured in code.
  • Default pins:
    • UART0 → GP0 (TX), GP1 (RX)
    • I2C0 → GP4 (SDA), GP5 (SCL)
    • SPI0 → GP16 (MISO), GP19 (MOSI), GP18 (SCK), GP17 (CS0)
  • Always set pins with gpio_set_function() and enable pull-ups for I2C.

  • Example: 

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    #include "pico/stdlib.h"
#include "hardware/i2c.h"
#include "hardware/uart.h"

int main() {
    // UART0: GP0(TX), GP1(RX)
    uart_init(uart0, 115200);
    gpio_set_function(0, GPIO_FUNC_UART);
    gpio_set_function(1, GPIO_FUNC_UART);

    // I2C0: GP20(SDA), GP21(SCL)
    i2c_init(i2c0, 100 * 1000); // 100kHz
    gpio_set_function(20, GPIO_FUNC_I2C);
    gpio_set_function(21, GPIO_FUNC_I2C);
    gpio_pull_up(20);
    gpio_pull_up(21);

    while (true) {
        // main loop
    }
}

SPI (Serial Peripheral Interface)

  • Notes
    • Uses separate lines for data in (MISO), data out (MOSI), clock (SCK), and a chip select (CS) for each device.
    • Master drives the clock; data is transferred simultaneously in both directions (full-duplex).
    • Very fast and simple but requires more pins.

  • Pin assignment

    Signal Description
    MOSI / COPI Master Out, Slave In / Center Out, Peripheral In: data from master to slave
    MISO / CIPO Master In, Slave Out / Center In, Peripheral Out: data from slave to master
    SCK / CLK Serial Clock (generated by master)
    CS / SS Chip Select or Slave Select (active low, one per slave)
    (Optional) GND, VCC, and sometimes INT or READY

  • Test: OLED SH1106 (SPI)

    SH1106 Pico Note
    GND GND Power
    VCC 3V3(OUT) Power
    SCK (CLK) 10 SPI clock line. Determines data timing.
    SDA (MOSI) 11 Data line. In SPI, Pico → OLED.
    RES 12 (Any GPIO) Reset pin. LOW → HIGH to initialize OLED.
    DC 13 (Any GPIO) Data/Command select. LOW = command, HIGH = data.
    CS 14 (Any GPIO) Chip Select (active LOW). Used if multiple SPI devices are present.
    - - *MISO is not used since OLED doesn't require out data to master.

  • First test: SH1106 128x64 SPi QTPY

  • Code: 

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    #include <U8g2lib.h>

int xPosText = 128;  // Initial horizontal position for the text
int xPosRect = 0;    // Initial horizontal position for the rectangles

// SH1106 128x64 SPI constructor (4-wire software SPI)
#define OLED_CS   9
#define OLED_DC   13
#define OLED_RST  12
#define OLED_SCK  10
#define OLED_MOSI 11

U8G2_SH1106_128X64_NONAME_F_4W_SW_SPI u8g2(U8G2_R0, /* clock=*/ OLED_SCK, /* data=*/ OLED_MOSI, /* cs=*/ OLED_CS, /* dc=*/ OLED_DC, /* reset=*/ OLED_RST);

void setup() {
    u8g2.begin();  // Initialize the display
}

void loop() {
    u8g2.clearBuffer();

    u8g2.setFont(u8g2_font_10x20_tr);
    u8g2.drawStr(xPosText, 38, "Konnichiwa, SH1106!");
    int textWidth = u8g2.getStrWidth("Konnichiwa, SH1106!");

    u8g2.drawBox(xPosRect, 20, 32, 2);
    u8g2.drawBox(xPosRect, 40, 64, 2);

    u8g2.sendBuffer();

    xPosText--;
    if (xPosText < -textWidth) {
        xPosText = 128;
    }

    xPosRect += 10;
    if (xPosRect > 128) {
        xPosRect = -64;
    }

    delay(10);
}

Ref: Motor driver breakout board