# 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. [HTML version](https://soldr.ai/blog) 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](https://soldr.ai/blog/code-that-reviews-its-own-wiring) · 2 September 2026A 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](https://soldr.ai/blog/pull-up-and-pull-down-resistors-why-floating-pins-lie) · 23 August 2026A 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](https://soldr.ai/blog/decoupling-capacitors-why-every-chip-wants-100nf) · 23 August 2026A 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](https://soldr.ai/blog/pwm-explained-how-one-digital-pin-fakes-an-analog-voltage) · 23 August 2026PWM 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](https://soldr.ai/blog/adc-resolution-what-10-bit-vs-12-bit-actually-buys-you) · 23 August 202610-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](https://soldr.ai/blog/voltage-dividers-and-the-loads-that-break-them) · 23 August 2026Two 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](https://soldr.ai/blog/the-transistor-as-a-switch-npn-basics-for-makers) · 23 August 2026An 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](https://soldr.ai/blog/mosfet-vs-bjt-choosing-the-right-switch) · 23 August 2026BJTs 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](https://soldr.ai/blog/how-relays-actually-work-coil-contacts-and-the-click) · 23 August 2026A 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](https://soldr.ai/blog/flyback-diodes-why-motors-and-relays-kill-pins) · 23 August 2026Switching 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](https://soldr.ai/blog/button-debouncing-hardware-and-software-fixes) · 23 August 2026A 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](https://soldr.ai/blog/inside-a-breadboard-how-the-rows-connect-and-why-contacts-fail) · 23 August 2026Each 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](https://soldr.ai/blog/multimeter-basics-measuring-voltage-current-and-resistance-without-frying-it) · 23 August 2026Voltage 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](https://soldr.ai/blog/series-vs-parallel-batteries-resistors-and-what-adds-up) · 23 August 2026In 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](https://soldr.ai/blog/led-current-limiting-resistors-the-2-minute-math) · 23 August 2026R = (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](https://soldr.ai/blog/common-ground-why-two-powered-circuits-ignore-each-other) · 23 August 2026Two 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](https://soldr.ai/blog/the-h-bridge-how-a-motor-learns-to-reverse) · 23 August 2026Four 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](https://soldr.ai/blog/37-sensors-one-box-what-the-37-in-1-arduino-kit-actually-teaches) · 23 August 2026The ₹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](https://soldr.ai/blog/your-first-connected-device-inside-the-esp32-smart-iot-kit) · 23 August 2026An 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](https://soldr.ai/blog/what-you-actually-build-with-the-obstacle-avoiding-robot-kit) · 23 August 2026A ₹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](https://soldr.ai/blog/drive-a-robot-by-tilting-your-hand-the-gesture-control-kit) · 23 August 2026Tilt 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](https://soldr.ai/blog/the-bluetooth-rc-car-kit-pwm-is-the-whole-point) · 23 August 2026A ₹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](https://soldr.ai/blog/four-motors-two-drivers-the-4wd-arduino-robot-kit) · 23 August 2026Four 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](https://soldr.ai/blog/what-you-actually-build-with-the-maze-solving-robot-kit) · 23 August 2026Two 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](https://soldr.ai/blog/push-dont-get-pushed-building-the-sumo-robot-kit) · 23 August 2026The 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](https://soldr.ai/blog/teaching-an-arm-to-see-colour-the-colour-sorting-robot-kit) · 23 August 2026A 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](https://soldr.ai/blog/the-ball-balancer-kit-pid-control-you-can-touch) · 23 August 2026A 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](https://soldr.ai/blog/the-cnc-plotter-kit-your-first-real-machine-tool) · 23 August 2026Two 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](https://soldr.ai/blog/three-knobs-three-joints-the-robotic-gripper-arm-kit) · 23 August 2026Three 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](https://soldr.ai/blog/a-camera-that-follows-things-the-vision-tracker-kit) · 23 August 2026An 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](https://soldr.ai/blog/eighteen-servos-and-a-gait-building-the-hexapod-robot-kit) · 23 August 2026Eighteen 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](https://soldr.ai/blog/robotics-underwater-the-arduino-rov-kit) · 23 August 2026Four 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](https://soldr.ai/blog/find-the-flame-inside-the-firefighter-robot-kit) · 23 August 2026Three 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](https://soldr.ai/blog/soldr-vs-grok-bot) · 22 August 2026Grok 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.