The rail is never as
quiet as the schematic says
Notes and measurements from the awkward space between firmware and copper, plus the calculators I got tired of re-deriving. Every tool states the standard it implements and the assumptions it makes, so you can check it instead of trusting it.
Tools
- Trace widthHow wide a trace has to be to carry a current without cooking.IPC-2221
- Resistor decoderColour bands and SMD codes, with the nearest preferred values.IEC 60062 / 60063
- RC filterCorner frequency, time constant, and the rise time you get with it.First-order passive
- Microstrip impedanceSingle-ended and differential impedance, and propagation delay.IPC-2141
- Voltage dividerOutput, current and dissipation, with the nearest real part.Ohm's law
- Baud rate errorEvery standard rate at your clock, and which ones the UART can hold.Integer-divisor UART
- ViaCurrent, resistance and thermal resistance of a plated hole.IPC-2221 / IPC-6012
- I²C pull-upThe resistor window between sink current and rise time.NXP UM10204
- Crystal loadC1 and C2 for a Pierce oscillator once stray capacitance is counted.ST AN2867
- LED resistorSeries resistor, standard value, power, and the worst-case current.Ohm's law
- Capacitor codeThree-digit codes, tolerance letters, voltage prefixes; reactance and energy.IEC 60062 / EIA-198
- Battery runtimeLife from a sleep/wake profile, with self-discharge and cell presets.Time-weighted average
- DecouplingA real capacitor across frequency, the PDN target, and how many parts hold it.Series RLC / target impedance