Engineering tools
Electronics tools
Calculators for the small decisions in circuit design: LED series resistors, voltage dividers, RC filters, 555 timers, heat sinks and junction temperature, battery life for low-power devices and PCB trace width, with the reasoning and the data behind each one.
Tools we reach for while designing and prototyping hardware. Each one states its formula, picks real standard component values rather than ideal ones, and says what it does not account for.
LED series resistor calculator
Find the series resistor for one LED or a string of LEDs from the supply voltage, forward voltage and current; pick the nearest E12 or E24 standard value, see the current it actually gives, and get the resistor power rating to use.
Open tool →Voltage divider calculator
Find R1 for a wanted output from a chosen R2, pick the nearest E12, E24 or E96 value, and see what the divider really delivers: the unloaded and loaded output, the current it draws, the power in each resistor, its Thévenin impedance and the worst case with resistor tolerance.
Open tool →RC low-pass filter calculator
Cutoff frequency and time constant from R and C, or the nearest standard R or C for a target cutoff; the attenuation and phase shift at the frequency you care about, the step response from 63 % to 99.9 %, and the −20 dB per decade roll-off in numbers.
Open tool →555 timer calculator (astable and monostable)
Frequency, period, high and low times and duty cycle of a 555 astable from R1, R2 and C; the nearest E-series R1 and R2 for a target frequency and duty; the monostable pulse width from R and C; with the discharge-pin current and the checks that catch a circuit that will not time as the formula says.
Open tool →Heat sink and junction temperature calculator
The heat sink thermal resistance a transistor, MOSFET, regulator or diode needs from its dissipation, the ambient in the enclosure and a design junction temperature; the junction, case and sink temperatures with the sink you have; the same device with no sink; and the power each can take.
Open tool →Battery life calculator for low-power devices
Estimate how long a sensor node or tracker will run on its battery: the average current from a sleep floor, wake and radio bursts, converter loss and self-discharge; the life in months; which drain dominates; and what doubling the events or halving the sleep current would do.
Open tool →PCB trace width calculator (IPC-2221)
Find the copper trace width a current needs for a chosen temperature rise on an external or internal layer, for 0.5 to 3 oz copper, with the IPC-2221 formula; then the trace's resistance, voltage drop and loss, and a check of a width you already have: what it carries and how hot it runs.
Open tool →Standard values, not ideal ones
A formula gives 500 Ω; a parts drawer gives 470 Ω or 510 Ω. The tools here finish the job by choosing a value from the E-series you actually stock, recalculating with that value, and checking the power rating, because a resistor that is electrically right but thermally marginal is the commonest small mistake on a prototype.