general

voltage divider

Vout = Vin × (R2 / (R1 + R2)) - leave one field empty to solve

enter 3 values to solve

parallel/series resistors

series: -
parallel: -

standard value finder (e-series)

Nearest standard resistor value to a calculated target - works for any E-series part

nearest: -
next below: -
next above: -

divider pair finder (e-series)

Best standard resistor pairs for a target Vout = Vin × R2 / (R1 + R2)

enter Vin and Vout

led current-limit resistor

R = (Vs - Vf) / If, rounded up to E24

exact R: -
E24 value: -
dissipation: -

rc charge time

Time for a capacitor charging toward Vs to cross Vth: t = -RC × ln(1 - Vth/Vs)

time constant τ: -
time to Vth: -

wire gauge (awg)

Copper wire resistance, one-way voltage drop, and rule-of-thumb ampacity (~4 A/mm² bundled, ~10 A/mm² in free air)

diameter: -
resistance: -
voltage drop: -
power loss: -
ampacity (bundled): -
ampacity (free air): -

embedded / digital

i2c pull-up resistors

Rmin from VOL sink current (0.4 V spec), Rmax from rise time: tr = 0.8473 × R × Cb. Standard mode 1000 ns, fast mode 300 ns

Rmin: -
Rmax: -
suggested (E24): -

crystal load capacitors

C1 = C2 = 2 × (CL - Cstray). CL from the crystal datasheet; stray is typically 3-5 pF of pin + trace capacitance

C1 = C2: -
nearest E24: -

adc resolution

LSB = Vref / 2^N, ideal SNR = 6.02N + 1.76 dB (full-scale sine)

LSB: -
levels: -
ideal SNR: -

ntc thermistor (β equation)

R = R25 × exp(β × (1/T - 1/298.15)) - fill T or R, leave the other empty to solve

enter R25 and β

mosfets

junction temperature

P = I² × Rds(on), Tj = Ta + (P × θja)

power: -
Tj: -

switching losses

Psw = Qg × Vgs × fsw, Pcond = I² × Rds(on)

switching: -
conduction: -
total: -

analog

opamp gain/bandwidth product

GBP = Gain × Bandwidth - leave one field empty to solve

enter 2 values to solve

low pass filter (RC)

fc = 1 / (2πRC) - leave one field empty to solve

enter 2 values to solve

sallen-key low pass (2nd order)

Unity-gain, equal-R design: C1 = 4Q² × C2, R1 = R2 = 1/(4πQ × fc × C2). Q = 0.707 for Butterworth

R1 = R2: -
nearest E96: -
C1: -

dbm / watts / volts

Sine-wave conversions at a given impedance: P = Vrms²/Z, Vpp = 2√2 × Vrms. Enter one value, leave the rest empty

enter exactly one of dBm / W / Vrms / Vpp

battery

battery life calculator

Estimates runtime based on capacity, sleep power, and TX events

runtime: -

power supplies

inductor sizing (buck converter)

L = (Vout × (Vin - Vout)) / (Vin × fsw × ΔI)

L: -
peak current: -

inductor sizing (boost converter)

D = 1 - Vin/Vout, L = (Vin × D) / (fsw × ΔIL). Note the inductor carries the input current: IL = Iout / (1 - D)

duty cycle: -
L: -
IL avg: -
IL peak: -

output capacitor (buck converter)

ΔVout = ΔIL × ESR + ΔIL / (8 × fsw × C). ΔIL from the inductor sizing calc above

ESR ripple: -
min C: -

linear regulator thermal

P = (Vin - Vout) × I, Tj = Ta + P × θja - the 'do I need a heatsink' check

dissipation: -
Tj: -
Imax @ Tj limit: -
efficiency (max): -

capacitor ripple current / esr heating

P = I²rms × ESR, estimates temperature rise

power: -
ΔT: -
cap temp: -

rc snubber designer

Measure the switch-node ring frequency (f1), add a test cap and measure again (f2). R = √(Lpar/Cpar), Csnub ≈ 3 × Cpar

parasitic C: -
parasitic L: -
snubber R: -
snubber C: -

pcb traces & vias

trace width (ipc-2221)

Minimum width for a current and allowed temperature rise: I = k × ΔT^0.44 × A^0.725. Resistance at 20 °C for the computed width

min width: -
resistance: -
voltage drop: -
power loss: -

trace impedance

Calculates characteristic impedance for microstrip or stripline

Z0: -

differential pair impedance

Edge-coupled pair (IPC-2141 approximation) - for USB, RS-485, Ethernet etc.

Z0 (single-ended): -
Zdiff: -

via current / resistance / inductance

Barrel treated as an internal IPC-2221 conductor. L ≈ 0.2 × h × (ln(4h/d) + 1) nH

ampacity: -
resistance: -
inductance: -