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Soldr Blog

Every Soldr post, newest first: pull-ups, decoupling, PWM, ADC resolution, brownouts and the builds that taught us, written from real sessions with real parts.

34 posts. Each one comes from a real build or a real question; every part named is one Soldr puts in a tray.

• Code that reviews its own wiring · 2 September 2026
  A sketch can compile and still not match your board. Soldr checks the firmware against the pin plan the wiring diagram came from, and names the mismatch.
• Pull-Up and Pull-Down Resistors: Why Floating Pins Lie · 23 August 2026
  A pull-up or pull-down resistor gives a digital input a definite resting voltage, so it reads a clean HIGH or LOW instead of random noise. Here's how.
• Decoupling Capacitors: Why Every Chip Wants 100nF · 23 August 2026
  A 100nF decoupling capacitor beside a chip's power pins acts as a tiny local battery, absorbing current spikes that otherwise cause resets and mystery bugs.
• PWM Explained: How One Digital Pin Fakes an Analog Voltage · 23 August 2026
  PWM fakes an analog voltage by switching a pin fully on and off very fast; the load feels the average. Duty cycle, frequency, and where the smoothing happens.
• ADC Resolution: What 10-Bit vs 12-Bit Actually Buys You · 23 August 2026
  10-bit gives 1024 steps, 12-bit gives 4096 — but more bits mean finer steps, not more accuracy. What ADC resolution actually buys you on Arduino and ESP32.
• Voltage Dividers, and the Loads That Break Them · 23 August 2026
  Two resistors set a fraction of the input voltage — until a load draws current and the output sags. How voltage dividers work, and the loads that break them.
• The Transistor as a Switch: NPN Basics for Makers · 23 August 2026
  An NPN transistor lets a 20mA Arduino pin switch loads that need hundreds of milliamps. Base resistors, saturation, and the standard low-side switch circuit.
• MOSFET vs BJT: Choosing the Right Switch · 23 August 2026
  BJTs suit small loads under 500mA; logic-level MOSFETs handle amps and stay cool. How to choose the right switch, and why an IRF540N on a 5V pin cooks itself.
• How Relays Actually Work: Coil, Contacts, and the Click · 23 August 2026
  A relay is an electromagnet pulling a mechanical switch, letting 5V logic switch a separate high-power circuit. Coil, COM/NO/NC contacts and isolation explained.
• Flyback Diodes: Why Motors and Relays Kill Pins · 23 August 2026
  Switching off a motor or relay coil fires a 100V+ spike that silently kills transistors and pins. One 1N4007 across the load absorbs it. Here's how and why.
• Button Debouncing: Hardware and Software Fixes · 23 August 2026
  A pressed button bounces a dozen times in milliseconds, so code counts five presses for one. Fix it with a 50ms software lockout or an RC filter in hardware.
• Inside a Breadboard: How the Rows Connect and Why Contacts Fail · 23 August 2026
  Each five-hole breadboard row is one metal clip, one node; the rails run power. How the connections map, and why worn clips cause faults that come and go.
• Multimeter Basics: Measuring Voltage, Current and Resistance Without Frying It · 23 August 2026
  Voltage in parallel, current in series, resistance with power off — the three rules that keep a multimeter alive, plus the classic mistake that blows the fuse.
• Series vs Parallel: Batteries, Resistors, and What Adds Up · 23 August 2026
  In series voltages add and current is shared; in parallel currents add and voltage is shared. Batteries, resistors, LEDs, and what actually adds up where.
• LED Current-Limiting Resistors: The 2-Minute Math · 23 August 2026
  R = (supply − forward voltage) ÷ current: the one-line math that sizes an LED's resistor, and why skipping it kills LEDs and quietly damages Arduino pins.
• Common Ground: Why Two Powered Circuits Ignore Each Other · 23 August 2026
  Two separately powered circuits can't read each other's signals without a shared ground reference. Why one GND-to-GND wire fixes motors, servos and sensors.
• The H-Bridge: How a Motor Learns to Reverse · 23 August 2026
  Four switches around a motor let current flow either way, so the motor reverses. How an H-bridge works, shoot-through, and driving an L298N from an Arduino.
• 37 Sensors, One Box: What the 37-in-1 Arduino Kit Actually Teaches · 23 August 2026
  The ₹940 37-in-1 sensor kit is a parts library, not one project: 37 modules covering light, sound, motion, temperature and distance for Arduino and ESP32.
• Your First Connected Device: Inside the ESP32 Smart IoT Kit · 23 August 2026
  An ESP32 with Wi-Fi and Bluetooth plus a 0.96in OLED for ₹810: the kit that makes your first connected device — dashboards, loggers, IoT displays — real.
• What You Actually Build with the Obstacle Avoiding Robot Kit · 23 August 2026
  A ₹1,995 kit that builds a 2WD robot that drives itself: HC-SR04 ultrasonic ranging, a servo-swept sensor, and classic avoidance logic on an Arduino Uno.
• Drive a Robot by Tilting Your Hand: The Gesture Control Kit · 23 August 2026
  Tilt your hand and the robot drives: a wrist-worn Nano with an MPU6050 streams tilt over HC-05 Bluetooth to a 2WD chassis. A true two-board build at ₹1,570.
• The Bluetooth RC Car Kit: PWM Is the Whole Point · 23 August 2026
  A ₹1,390 Bluetooth RC car kit whose real subject is proportional control: joystick coordinates from a phone become graded PWM so the car drives, not lurches.
• Four Motors, Two Drivers: The 4WD Arduino Robot Kit · 23 August 2026
  Four TT motors, two L298N drivers and ultrasonic avoidance on a ₹1,320 4WD chassis — a rough-ground robot platform and a lesson in power-noise discipline.
• What You Actually Build with the Maze Solving Robot Kit · 23 August 2026
  Two ultrasonic sensors and the left-hand wall-following rule: a ₹1,775 beginner kit that builds a robot which provably solves any simply connected maze.
• Push, Don't Get Pushed: Building the Sumo Robot Kit · 23 August 2026
  The cheapest robot in the range at ₹914: four IR sensors, an Arduino Uno and a push-them-out strategy, built to the 10 cm, 500 g mini sumo competition spec.
• Teaching an Arm to See Colour: The Colour Sorting Robot Kit · 23 August 2026
  A TCS3200 colour sensor reads red, green or blue and a two-servo arm sweeps each object into its bin — desktop industrial sorting for ₹1,200, no soldering.
• The Ball Balancer Kit: PID Control You Can Touch · 23 August 2026
  A steel ball, a tilting beam, an MPU6050 and your PID loop holding it centred: control theory you can touch, tune and nudge, in a ₹2,660 desktop rig.
• The CNC Plotter Kit: Your First Real Machine Tool · 23 August 2026
  Two NEMA17 steppers, GRBL firmware and a servo pen-lift build an A4 drawing machine — the ₹5,040 kit where Arduino projects become real machine tools.
• Three Knobs, Three Joints: The Robotic Gripper Arm Kit · 23 August 2026
  Three potentiometer knobs drive three servo joints in real time, plus a gripper: a ₹1,420 robotic arm whose core motion needs no coding at all to start.
• A Camera That Follows Things: The Vision Tracker Kit · 23 August 2026
  An OpenMV Cam runs blob detection on-board and an Arduino steers a pan-tilt gimbal to follow the target — embedded computer vision for ₹1,090, iron included.
• Eighteen Servos and a Gait: Building the Hexapod Robot Kit · 23 August 2026
  Eighteen servos, two PCA9685 drivers, an IMU and inverse kinematics: the ₹9,770 capstone kit that builds a six-legged walking robot from the ground up.
• Robotics Underwater: The Arduino ROV Kit · 23 August 2026
  Four bilge-pump thrusters, a sealed enclosure and a tethered joystick controller: a ₹2,760 Arduino Mega kit that takes robotics below the waterline.
• Find the Flame: Inside the Firefighter Robot Kit · 23 August 2026
  Three flame sensors triangulate a candle, the robot drives to it and a fan blows it out — a ₹1,775 beginner kit that senses, navigates and acts on its own.
• Soldr vs Grok Bot: what ₹150 buys against $120 a month · 22 August 2026
  Grok Bot runs general agents at $120-300 a month. Soldr builds your hardware idea end to end, pay-per-use capped at ₹150, and ships the real parts COD across India.