The Artoo Maker Lab tools hub puts five everyday electronics helpers on one page: a GPIO pinout explorer, an Ohm’s law calculator, a resistor colour code calculator, an LED resistor calculator and a number base converter for binary, decimal, hex and octal. Everything runs in your browser, so you can keep it open next to your breadboard and check a value before you wire it.
How to use it
- Choose the tool that matches the job: identifying a pin, solving for voltage, current or resistance, reading resistor bands, sizing an LED resistor or converting a number between bases.
- Enter the values you already know. For Ohm’s law that means any two of voltage, current and resistance. For the LED calculator that means supply voltage, LED forward voltage and target current.
- Check your units before reading the answer. Milliamps and amps differ by a factor of 1,000, and that mistake is easy to make.
- Read the result and compare it with your parts. If a calculated resistor value isn’t one you own, round up to the next value you have.
- Confirm with a multimeter on the real circuit, especially before connecting anything to a microcontroller pin.
The electronics behind each tool
Ohm’s law. Voltage equals current multiplied by resistance: V = I × R. Rearranged, I = V ÷ R and R = V ÷ I. Power follows from P = V × I, which is how you check that a resistor’s wattage rating is high enough. A resistor dropping 3 V at 20 mA dissipates 0.06 W, well inside the rating of a common 0.25 W part.
Resistor colour codes. The bands follow the IEC 60062 standard. The digit colours are black 0, brown 1, red 2, orange 3, yellow 4, green 5, blue 6, violet 7, grey 8 and white 9. On a four-band resistor, the first two bands are digits, the third is the multiplier (a power of ten, with gold meaning ×0.1 and silver ×0.01) and the fourth is tolerance. Common tolerances are brown ±1%, red ±2%, gold ±5% and silver ±10%. Five-band resistors add a third digit before the multiplier. Brown, black, red, gold reads as 10 × 100 = 1,000 Ω at ±5%. Yellow, violet, orange reads as 47 × 1,000 = 47 kΩ.
LED resistors. An LED drops a roughly fixed forward voltage, and the resistor takes the rest. The formula is R = (supply voltage − forward voltage) ÷ current. A red LED with a 2.0 V forward voltage on a 5 V supply at 20 mA needs (5 − 2) ÷ 0.02 = 150 Ω. Forward voltage depends on colour and on the specific part. Red is typically around 1.8 to 2.2 V, while blue and white are usually near 3 V or higher. Take the figure from your LED’s datasheet when you have one.
GPIO pinouts. Boards often have two numbering schemes, one for the physical pin position and one for the chip’s GPIO number, and mixing them up is the most common wiring error. On a Raspberry Pi 40-pin header, for example, physical pin 11 is GPIO 17. Logic voltage matters too. Raspberry Pi GPIO runs at 3.3 V and is not 5 V tolerant, so feeding 5 V into an input pin can damage the board.
Number bases. Binary (base 2), octal (base 8), decimal (base 10) and hexadecimal (base 16) are all positional systems. The only thing that changes between them is the value of each digit position. The decimal number 255 is 11111111 in binary, 377 in octal and FF in hex. That makes hex a compact way to write byte values, register addresses and colour codes.
What the hub does not do. It doesn’t measure your components, detect which board you have plugged in, simulate a circuit or check your wiring. Results are only as accurate as the values you enter, and real resistors vary within their tolerance band.
FAQ
Why does my LED calculation give a value I can’t buy?
Resistors are made in standard series such as E12 and E24, so exact calculated values are often unavailable. Round up to the next standard value. That slightly lowers the current, which is the safe direction for the LED.
Can I use the Ohm’s law calculator for AC circuits?
It applies directly to resistive loads. Circuits with capacitors or inductors involve impedance, which changes with frequency, and this calculator doesn’t model that.
What if my resistor’s bands are hard to read?
Faded or ambiguous colours, especially red versus orange or brown versus violet, are a known problem. Find the tolerance band, usually gold or silver and slightly separated, and read from the opposite end. If you’re still unsure, measure the resistor with a multimeter.
Does the converter replace a programmer’s calculator?
It covers conversion between binary, decimal, hex and octal, which handles most maker tasks like reading I2C addresses or register values. For bitwise operations or arithmetic across bases, a dedicated programmer’s calculator is the better choice.