Pick a circuit block on the left and adjust the requirements below — the resistor and capacitor values are computed live from real design formulas, then snapped to standard (E12) part values, the way you'd actually buy them.
LED current-limiting resistor
Solves R = (Vsupply − Vf) / I for a single LED, then rounds up to the nearest standard resistor so the LED never exceeds your target current.
Supply voltage must exceed the LED's forward voltage.
Calculated R—
Standard part (E12)—
Actual current—
Resistor power—
555 astable blinker / oscillator
Solves the classic 555 astable equations for R1 and R2 given a target frequency, duty cycle, and timing capacitor, then snaps both resistors to E12 values and reports the frequency you'd actually get.
Classic 555 astable topology only reaches duty ≥ 50% — for lower duty, a diode across R1 is required (not modeled here).
R1 (standard)—
R2 (standard)—
Actual frequency—
Actual duty—
Linear regulator power supply
Computes the power a linear regulator has to burn off as heat (Pd = (Vin − Vout) × Iout) and flags when a TO-220 package needs a heatsink.
Input voltage must exceed output plus ~1.5 V dropout.
Power dissipated—
Heatsink—
Input cap—
Output cap—