# Soldr — all pages

> An AI hardware design tool. Describe what you want to build and Soldr designs it end to end — parts that are really in stock, wiring, schematic, firmware for 674 boards, display artwork and dashboards. The parts it picks can be ordered and shipped to you.

Every page below is also available as markdown: append .md to the URL.

- [Build hardware with AI. Every part real.](https://soldr.ai/) — [markdown](https://soldr.ai/index.md): The product homepage. What Soldr does, a worked build with real prices, the boards it supports, pricing, and how component suppliers can supply us wholesale.
- [Soldr Docs](https://soldr.ai/docs) — [markdown](https://soldr.ai/docs.md): Index of every how-to guide. Grouped by starting a build, when it does not work, and screens and dashboards.
- [Soldr Blog](https://soldr.ai/blog) — [markdown](https://soldr.ai/blog.md): Index of every Soldr blog post, newest first, with a one-line summary of each.
- [Your ESP32 reboots the moment the motor starts](https://soldr.ai/docs/esp32-reboots-when-motor-starts) — [markdown](https://soldr.ai/docs/esp32-reboots-when-motor-starts.md): Diagnoses the ESP32 brownout reset when an inductive load switches on. Covers separate supply, common ground, bulk capacitance, driving the load through a MOSFET, and a worked 12V build.
- [It compiled. It flashed. The board still won't boot.](https://soldr.ai/docs/esp32-s3-flashed-but-wont-boot) — [markdown](https://soldr.ai/docs/esp32-s3-flashed-but-wont-boot.md): Explains the ESP32-S3 boot loop that prints 'Invalid image block, can't boot' after a successful compile and flash. Decodes the ROM boot log: rst:0x7 TG0WDT_SYS_RST is the watchdog looping, not the cause; the diagnostic line is the second 'load:' segment, whose length (e.g. 0x3cc11c40, about 972MB) is impossible and whose address is unaligned, meaning the loader lost its place in the image header. Key point: a successful flash verifies the write, not the boot - the ROM re-reads the bytes later using the flash mode, speed and size in the image header. Fixes in order: flash size must match the module, PSRAM type must match (OPI for R8 modules), flash mode, then flash frequency; then erase the whole chip and reflash. Notes that module suffixes matter - N16R8 is 16MB flash plus 8MB octal PSRAM and is not interchangeable with a generic ESP32-S3 selection.
- [Your Serial Monitor shows garbage or a crash dump — here's how to actually read it](https://soldr.ai/docs/reading-serial-monitor-output) — [markdown](https://soldr.ai/docs/reading-serial-monitor-output.md): Explains how to read ESP32/Arduino serial monitor output: a baud-rate mismatch producing garbled text, a Guru Meditation crash with a backtrace, and clean repeating reboots pointing to a brownout (linked to a dedicated guide). Shows pasting serial output into Soldr for a diagnosis grounded in the actual flashed sketch.
- [You've checked the wiring three times and it still doesn't work — try a photo instead](https://soldr.ai/docs/photograph-your-breadboard) — [markdown](https://soldr.ai/docs/photograph-your-breadboard.md): Explains why wiring mistakes (reversed LED polarity, a one-row breadboard slip, a wrong component) are often invisible in a written checklist but obvious in a photo. Shows uploading a breadboard photo to Soldr's vision diagnosis for a second pair of eyes.
- [Numbers scrolling past too fast to make sense of? Watch them as a graph instead](https://soldr.ai/docs/watching-sensor-readings-live) — [markdown](https://soldr.ai/docs/watching-sensor-readings-live.md): Explains why watching sensor readings as a live graph (serial plotter) reveals noise, drift, and thresholds that a scrolling text column hides. Worked example: calibrating an LDR day/night threshold from the graph's measured extremes rather than a guessed number.
- [How do you know which pin to use — and why does it actually matter?](https://soldr.ai/docs/wiring-and-pins) — [markdown](https://soldr.ai/docs/wiring-and-pins.md): Explains why generic wiring advice ('use any digital pin') fails: strapping pins that affect boot, shared I2C bus addresses, and fixed-function pins. Shows how wiring generated for the exact named board avoids all three, with a worked two-sensor I2C example.
- [Your own IDE won't compile it — even though the code is already working. Here's why.](https://soldr.ai/docs/sketch-wont-compile) — [markdown](https://soldr.ai/docs/sketch-wont-compile.md): Explains that generated code (674 supported board targets) can be flashed directly from the browser with nothing installed, or taken into the user's own IDE. A compile error in the user's own IDE is almost always a local toolchain difference (missing board package, local library version, a hand-edit) rather than a defect in the code. Covers reading and reporting a local compile error effectively.
- [How do you get a custom icon or animation onto a tiny display — without hand-encoding every byte?](https://soldr.ai/docs/pixel-studio-design-to-firmware) — [markdown](https://soldr.ai/docs/pixel-studio-design-to-firmware.md): Explains why hand-authoring pixel bytes for a display is error-prone (SSD1306 horizontal bitmap, MAX7219 per-row bytes, WS2812 RGB-per-LED in wire order are all different layouts), and shows designing icons/animations in Pixel Studio (7 presets across 3 display families, up to 60s frame durations, byte-budget warning for AVR boards) and exporting a ready-to-include .h header with a non-blocking millis()-based player. Fully client-side, no model in the pixel path, zero credits. Worked example: ESP32-DevKitC + 0.96in SSD1306 OLED, a blinking 16x16 thermometer icon.
- [How do Soldr credits actually work — and what do they cost?](https://soldr.ai/docs/credits-and-pricing) — [markdown](https://soldr.ai/docs/credits-and-pricing.md): Explains Soldr's credit system: 25 credits granted on sign-in, questions/troubleshooting/diagnosis always free, the first code generation free regardless of size, then billed at 1 credit per 200 billable tokens capped at 150 credits per generation, wiring diagrams billed separately by the same formula. Buying more is a one-time purchase (100/299/999 credit packs, 1 credit = INR 1), no subscription. All figures verified against the deployed worker's credit constants, not recalled from memory.
- [What actually happens when you describe a build to Soldr, start to finish?](https://soldr.ai/docs/your-first-build) — [markdown](https://soldr.ai/docs/your-first-build.md): A real, run-live guest session on the Soldr chat path, quoted verbatim: describing a weather-station idea in one sentence, Soldr asking a clarifying platform question rather than guessing, the returned build (ESP32-WROOM-32 + DHT11 + OLED + jumper wires + an extra TFT touch screen) with real Compoden prices, and Soldr's own 'Common problems' self-check flagging a voltage mismatch and a redundant second display in its own list. Explains that the parts stage is free and code generation requires signing in, linking to the credits guide for the exact billing formula.
- [What does Soldr actually do, end to end?](https://soldr.ai/docs/what-soldr-does) — [markdown](https://soldr.ai/docs/what-soldr-does.md): Overview/map page for Soldr: describes the end-to-end capability set (parts card, wiring, schematic, code for 674 boards, Pixel Studio, screen layout, dashboard preview, always-free questions), the flash-from-browser-or-own-IDE flow, and pricing at a glance, linking out to the detailed guide for each piece. Serves as the top-level orientation page for the docs section.
- [How do you design exactly what your display shows — without writing the draw code yourself?](https://soldr.ai/docs/screen-layout-design-tab) — [markdown](https://soldr.ai/docs/screen-layout-design-tab.md): Explains the Design tab (marketing name: Screen layout) — a display-gated build editor for composing text, live-sensor-bound values, bars and icons onto a 128x64 SSD1306 OLED already in the build's tray, distinct from Pixel Studio (single icon/animation asset vs a live composed layout). Covers binding elements to real sensor readings via suggested keys, Apply saving the layout to the build artifact without generating firmware itself, and the next code generation deterministically emitting a drawDesign() function from the exact layout. No separate credit charge for Apply. Worked example: ESP32-DevKitC + 0.96in SSD1306 OLED.
- [That page is not here](https://soldr.ai/404) — [markdown](https://soldr.ai/404.md): 404 page. Not content — if you reached this, the URL was wrong.
- [Code that reviews its own wiring](https://soldr.ai/blog/code-that-reviews-its-own-wiring) — [markdown](https://soldr.ai/blog/code-that-reviews-its-own-wiring.md): Compiling proves grammar, not that firmware matches the wiring. Soldr checks the generated sketch against the pin plan the schematic was drawn from and names the pin and part when they disagree; where no verified pinout exists it refuses to guess.
- [Soldr vs Grok Bot: what ₹150 buys against $120 a month](https://soldr.ai/blog/soldr-vs-grok-bot) — [markdown](https://soldr.ai/blog/soldr-vs-grok-bot.md): Honest comparison of Soldr and SpaceXAI's Grok Bot for hardware builds: subscription agents ($120-300/mo) vs purpose-built pay-per-use (Rs 1/credit, Rs 150 cap) grounded in a real shipped-parts catalogue.
- [Pull-Up and Pull-Down Resistors: Why Floating Pins Lie](https://soldr.ai/blog/pull-up-and-pull-down-resistors-why-floating-pins-lie) — [markdown](https://soldr.ai/blog/pull-up-and-pull-down-resistors-why-floating-pins-lie.md): 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](https://soldr.ai/blog/decoupling-capacitors-why-every-chip-wants-100nf) — [markdown](https://soldr.ai/blog/decoupling-capacitors-why-every-chip-wants-100nf.md): 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](https://soldr.ai/blog/pwm-explained-how-one-digital-pin-fakes-an-analog-voltage) — [markdown](https://soldr.ai/blog/pwm-explained-how-one-digital-pin-fakes-an-analog-voltage.md): 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](https://soldr.ai/blog/adc-resolution-what-10-bit-vs-12-bit-actually-buys-you) — [markdown](https://soldr.ai/blog/adc-resolution-what-10-bit-vs-12-bit-actually-buys-you.md): 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](https://soldr.ai/blog/voltage-dividers-and-the-loads-that-break-them) — [markdown](https://soldr.ai/blog/voltage-dividers-and-the-loads-that-break-them.md): 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](https://soldr.ai/blog/the-transistor-as-a-switch-npn-basics-for-makers) — [markdown](https://soldr.ai/blog/the-transistor-as-a-switch-npn-basics-for-makers.md): 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](https://soldr.ai/blog/mosfet-vs-bjt-choosing-the-right-switch) — [markdown](https://soldr.ai/blog/mosfet-vs-bjt-choosing-the-right-switch.md): 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](https://soldr.ai/blog/how-relays-actually-work-coil-contacts-and-the-click) — [markdown](https://soldr.ai/blog/how-relays-actually-work-coil-contacts-and-the-click.md): 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](https://soldr.ai/blog/flyback-diodes-why-motors-and-relays-kill-pins) — [markdown](https://soldr.ai/blog/flyback-diodes-why-motors-and-relays-kill-pins.md): 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](https://soldr.ai/blog/button-debouncing-hardware-and-software-fixes) — [markdown](https://soldr.ai/blog/button-debouncing-hardware-and-software-fixes.md): 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](https://soldr.ai/blog/inside-a-breadboard-how-the-rows-connect-and-why-contacts-fail) — [markdown](https://soldr.ai/blog/inside-a-breadboard-how-the-rows-connect-and-why-contacts-fail.md): 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](https://soldr.ai/blog/multimeter-basics-measuring-voltage-current-and-resistance-without-frying-it) — [markdown](https://soldr.ai/blog/multimeter-basics-measuring-voltage-current-and-resistance-without-frying-it.md): 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](https://soldr.ai/blog/series-vs-parallel-batteries-resistors-and-what-adds-up) — [markdown](https://soldr.ai/blog/series-vs-parallel-batteries-resistors-and-what-adds-up.md): 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](https://soldr.ai/blog/led-current-limiting-resistors-the-2-minute-math) — [markdown](https://soldr.ai/blog/led-current-limiting-resistors-the-2-minute-math.md): 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](https://soldr.ai/blog/common-ground-why-two-powered-circuits-ignore-each-other) — [markdown](https://soldr.ai/blog/common-ground-why-two-powered-circuits-ignore-each-other.md): 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](https://soldr.ai/blog/the-h-bridge-how-a-motor-learns-to-reverse) — [markdown](https://soldr.ai/blog/the-h-bridge-how-a-motor-learns-to-reverse.md): 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](https://soldr.ai/blog/37-sensors-one-box-what-the-37-in-1-arduino-kit-actually-teaches) — [markdown](https://soldr.ai/blog/37-sensors-one-box-what-the-37-in-1-arduino-kit-actually-teaches.md): 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](https://soldr.ai/blog/your-first-connected-device-inside-the-esp32-smart-iot-kit) — [markdown](https://soldr.ai/blog/your-first-connected-device-inside-the-esp32-smart-iot-kit.md): 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](https://soldr.ai/blog/what-you-actually-build-with-the-obstacle-avoiding-robot-kit) — [markdown](https://soldr.ai/blog/what-you-actually-build-with-the-obstacle-avoiding-robot-kit.md): 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](https://soldr.ai/blog/drive-a-robot-by-tilting-your-hand-the-gesture-control-kit) — [markdown](https://soldr.ai/blog/drive-a-robot-by-tilting-your-hand-the-gesture-control-kit.md): 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](https://soldr.ai/blog/the-bluetooth-rc-car-kit-pwm-is-the-whole-point) — [markdown](https://soldr.ai/blog/the-bluetooth-rc-car-kit-pwm-is-the-whole-point.md): 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](https://soldr.ai/blog/four-motors-two-drivers-the-4wd-arduino-robot-kit) — [markdown](https://soldr.ai/blog/four-motors-two-drivers-the-4wd-arduino-robot-kit.md): 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](https://soldr.ai/blog/what-you-actually-build-with-the-maze-solving-robot-kit) — [markdown](https://soldr.ai/blog/what-you-actually-build-with-the-maze-solving-robot-kit.md): 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](https://soldr.ai/blog/push-dont-get-pushed-building-the-sumo-robot-kit) — [markdown](https://soldr.ai/blog/push-dont-get-pushed-building-the-sumo-robot-kit.md): 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](https://soldr.ai/blog/teaching-an-arm-to-see-colour-the-colour-sorting-robot-kit) — [markdown](https://soldr.ai/blog/teaching-an-arm-to-see-colour-the-colour-sorting-robot-kit.md): 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](https://soldr.ai/blog/the-ball-balancer-kit-pid-control-you-can-touch) — [markdown](https://soldr.ai/blog/the-ball-balancer-kit-pid-control-you-can-touch.md): 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](https://soldr.ai/blog/the-cnc-plotter-kit-your-first-real-machine-tool) — [markdown](https://soldr.ai/blog/the-cnc-plotter-kit-your-first-real-machine-tool.md): 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](https://soldr.ai/blog/three-knobs-three-joints-the-robotic-gripper-arm-kit) — [markdown](https://soldr.ai/blog/three-knobs-three-joints-the-robotic-gripper-arm-kit.md): 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](https://soldr.ai/blog/a-camera-that-follows-things-the-vision-tracker-kit) — [markdown](https://soldr.ai/blog/a-camera-that-follows-things-the-vision-tracker-kit.md): 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](https://soldr.ai/blog/eighteen-servos-and-a-gait-building-the-hexapod-robot-kit) — [markdown](https://soldr.ai/blog/eighteen-servos-and-a-gait-building-the-hexapod-robot-kit.md): 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](https://soldr.ai/blog/robotics-underwater-the-arduino-rov-kit) — [markdown](https://soldr.ai/blog/robotics-underwater-the-arduino-rov-kit.md): 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](https://soldr.ai/blog/find-the-flame-inside-the-firefighter-robot-kit) — [markdown](https://soldr.ai/blog/find-the-flame-inside-the-firefighter-robot-kit.md): 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.