How do I read a resistor's colour bands?

Use the Resistor Color Code Calculator: choose the colour of each band for a 4-band or 5-band resistor and it returns the resistance and tolerance and draws the bands. Bands are usually read from the end where they sit closest together, with the more widely spaced tolerance band last.

Why does my serial output show garbage when both ends use the same baud rate?

The actual baud rate comes from dividing the clock, and a crystal that does not divide evenly leaves a timing error. Once the error grows past a few percent, characters are misread. The Baud Rate Calculator shows the error for your crystal and baud rate and the prescaler values to use.

How accurate is the battery life estimate?

It divides battery capacity by average current, so it is only as good as the current figure you give it. Measure the average current over a full cycle including sleep, and expect real life to come out shorter because of self-discharge and temperature.

What is the difference between a CRC and a hash?

A CRC detects accidental changes such as transmission errors and is cheap enough for small microcontrollers. A cryptographic hash such as SHA-256 is designed to resist deliberate tampering. The CRC Calculator supports CRC-8, CRC-16 variants including MODBUS, CRC-32 and custom polynomials; the hash generator is in the developer tools.

Which boards have a pinout reference?

The ESP32 WROOM-32, the Arduino Uno R3 and the Raspberry Pi 40-pin GPIO header. They show which pins carry digital, analog, PWM, SPI, I2C, UART, interrupt or touch functions, and the Raspberry Pi page includes both BCM and physical numbering.

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Free Embedded / Electronics

Electronics and embedded-systems tools: read a resistor from its colour bands, solve Ohm's law, size a voltage divider, set the frequency of a 555 timer, work out UART timing and baud-rate error for a crystal, estimate how long a battery will last in an Arduino or ESP32 project, and compute CRC checksums or IEEE 754 bit patterns when you are debugging a protocol or a firmware bug.

There are also pinout references for the ESP32, the Arduino Uno and the Raspberry Pi GPIO header, an ASCII table, and a number-base converter with 8, 16, 32 and 64-bit widths. Everything runs in the page, so it is quick to open on a bench laptop, and none of your design values are sent anywhere.

14 tools available

Most Popular

Resistor Color Code Calculator

Decode resistor color bands instantly. Supports 4-band and 5-band resistors with tolerance and visual band display.

Try it free →Ohm's Law Calculator

Calculate voltage, current, resistance, or power using Ohm's Law. Solve for any variable by entering the other two.

Try it free →555 Timer Calculator

Calculate frequency, duty cycle, and timing for 555 timer circuits. Supports astable and monostable modes.

Try it free →

Which tool should I use?

Reading a resistor: Resistor Color Code Calculator — 4-band and 5-band resistors with tolerance and a drawing of the bands.
Voltage, current, resistance or power: Ohm's Law Calculator — enter any two and it solves for the others.
Scaling a voltage down: Voltage Divider Calculator — output voltage or resistor values, with a circuit diagram.
A 555 timer circuit: 555 Timer Calculator — frequency, duty cycle and timing in astable and monostable modes.
UART timing: Baud Rate Calculator — bit and frame time, baud-rate error for your crystal, STM32 prescaler values.
Battery life of a device: Battery Life Calculator — 18650, LiPo, AA or custom cells for Arduino, ESP32 and IoT builds.
Servo or PWM settings: PWM Servo Calculator — pulse width, duty cycle and angle, with a 16-bit timer count.
A checksum for a protocol: CRC Calculator — CRC-8, CRC-16 variants including MODBUS, CRC-32 and custom polynomials.
How a float is stored: IEEE 754 Converter — 32-bit and 64-bit representations with colour-coded bit fields.
Hex, binary and decimal at a fixed width: Embedded Number Converter — 8 to 64-bit widths with the byte breakdown.
Which pin does what: ESP32 Pinout Reference — GPIO, ADC, SPI, I2C, UART and touch pins you can filter by function; Arduino Uno and Raspberry Pi references sit alongside it.
Looking up a character code: ASCII Table — decimal, hex, octal and binary values, filterable by printable or control characters.

All Embedded / Electronics (14)

Resistor Color Code Calculator

Decode resistor color bands instantly. Supports 4-band and 5-band resistors with tolerance and visual band display.

Open tool →Ohm's Law Calculator

Calculate voltage, current, resistance, or power using Ohm's Law. Solve for any variable by entering the other two.

Open tool →Voltage Divider Calculator

Calculate output voltage or resistor values for a resistor voltage divider. Includes SVG circuit diagram.

Open tool →555 Timer Calculator

Calculate frequency, duty cycle, and timing for 555 timer circuits. Supports astable and monostable modes.

Open tool →CRC Calculator

Calculate CRC checksums online. Supports CRC-8, CRC-16/CCITT, CRC-16/MODBUS, CRC-32, and custom polynomials.

Open tool →IEEE 754 Converter

Convert decimal numbers to IEEE 754 floating point representation (32-bit float, 64-bit double) with color-coded bit fields.

Open tool →ASCII Table

Complete ASCII character table with decimal, hex, octal, and binary values. Filter by printable or control characters.

Open tool →Baud Rate Calculator

Calculate UART bit timing, frame time, baud rate error for any crystal, and STM32 prescaler values.

Open tool →Battery Life Calculator

Estimate battery life for Arduino, ESP32, and IoT devices. Supports 18650, LiPo, AA, and custom batteries.

Open tool →PWM Servo Calculator

Calculate PWM pulse width, duty cycle, and servo angle. Convert angle to duty or pulse to angle with 16-bit timer count.

Open tool →Embedded Number Converter

Convert numbers between hex, decimal, binary, and octal with 8/16/32/64-bit widths. Shows byte breakdown and bit layout.

Open tool →ESP32 Pinout Reference

Complete ESP32 WROOM-32 pinout with GPIO, ADC, SPI, I2C, UART, and touch pins. Filter and search by function.

Open tool →Arduino Pinout Reference

Complete Arduino Uno R3 pinout with digital, analog, PWM, SPI, I2C, UART, and interrupt pins. Click for details.

Open tool →Raspberry Pi GPIO Pinout

Complete Raspberry Pi 40-pin GPIO reference with BCM/physical numbering, physical header view, and bus quick reference.

Open tool →

Frequently Asked Questions

How do I read a resistor's colour bands?: Use the Resistor Color Code Calculator: choose the colour of each band for a 4-band or 5-band resistor and it returns the resistance and tolerance and draws the bands. Bands are usually read from the end where they sit closest together, with the more widely spaced tolerance band last.
Why does my serial output show garbage when both ends use the same baud rate?: The actual baud rate comes from dividing the clock, and a crystal that does not divide evenly leaves a timing error. Once the error grows past a few percent, characters are misread. The Baud Rate Calculator shows the error for your crystal and baud rate and the prescaler values to use.
How accurate is the battery life estimate?: It divides battery capacity by average current, so it is only as good as the current figure you give it. Measure the average current over a full cycle including sleep, and expect real life to come out shorter because of self-discharge and temperature.
What is the difference between a CRC and a hash?: A CRC detects accidental changes such as transmission errors and is cheap enough for small microcontrollers. A cryptographic hash such as SHA-256 is designed to resist deliberate tampering. The CRC Calculator supports CRC-8, CRC-16 variants including MODBUS, CRC-32 and custom polynomials; the hash generator is in the developer tools.
Which boards have a pinout reference?: The ESP32 WROOM-32, the Arduino Uno R3 and the Raspberry Pi 40-pin GPIO header. They show which pins carry digital, analog, PWM, SPI, I2C, UART, interrupt or touch functions, and the Raspberry Pi page includes both BCM and physical numbering.