calculators
Calculators that show their working.
Every one of these prints the math step by step and then runs the circuit on a breadboard, so you see the number and what it does.
Ohm's law
V = I × R in all three directions — pick what you want to find, type the other two, watch the loop prove it. LED resistor
Which resistor keeps an LED alive on your battery, and how bright it will be. Voltage divider
Two resistors, one smaller voltage — the trick behind every sensor circuit. 555 timer frequency
R1, R2 and C in, blink rate and duty cycle out, chip running live. Resistor color code
Read a resistor by its color bands, or type a value and see which bands to look for. RC time constant
Resistor and capacitor in, τ = R·C out, with the charge curve drawn beneath. Series and parallel resistors
Combine two or three resistors end-to-end or side-by-side and see the equivalent value and the current the battery pushes. Capacitor code
Decode the three-digit number on a ceramic disc or MLCC, or type a value in µF and see which code to look for. Transistor base resistor
Size the resistor that pushes an NPN into saturation — your load's current, the worst-case hFE, and the switch running live. Battery life
How many hours or days your pack will run — datasheet ideal and the honest bench number, side by side. Power dissipation
How much heat a resistor turns into, which wattage you need, and when the paint starts to darken.
V = I × R in all three directions — pick what you want to find, type the other two, watch the loop prove it. LED resistor
Which resistor keeps an LED alive on your battery, and how bright it will be. Voltage divider
Two resistors, one smaller voltage — the trick behind every sensor circuit. 555 timer frequency
R1, R2 and C in, blink rate and duty cycle out, chip running live. Resistor color code
Read a resistor by its color bands, or type a value and see which bands to look for. RC time constant
Resistor and capacitor in, τ = R·C out, with the charge curve drawn beneath. Series and parallel resistors
Combine two or three resistors end-to-end or side-by-side and see the equivalent value and the current the battery pushes. Capacitor code
Decode the three-digit number on a ceramic disc or MLCC, or type a value in µF and see which code to look for. Transistor base resistor
Size the resistor that pushes an NPN into saturation — your load's current, the worst-case hFE, and the switch running live. Battery life
How many hours or days your pack will run — datasheet ideal and the honest bench number, side by side. Power dissipation
How much heat a resistor turns into, which wattage you need, and when the paint starts to darken.