Circuit calculators
Each one computes the numbers AND shows the real circuit they belong to — with a one-click path to designing it for real.
LED resistor
Series resistor, nearest standard value, actual current and power.
Voltage divider
Output voltage, output impedance, standing current — plus reverse mode.
Crystal load capacitors
The two caps from rated CL and board strays.
NTC thermistor table
Resistance, divider ratio, and ADC counts across temperature.
Op-amp gain
Non-inverting and inverting gain; reverse mode picks standard resistors.