Guides
Electronics guides
Short explanations of circuit-level decisions: LED resistors, voltage dividers and loading, RC filters, the 555 timer, keeping power parts cool, power budgeting for battery devices, PCB trace width, and what changes when a prototype has to ship.
Written from the bench rather than the textbook: each guide answers one design question, gives the numbers, and points to the electronics calculator that does the arithmetic.
Choosing an LED series resistor
Why an LED cannot be connected straight to a supply, how the series resistor sets the current, what forward voltage really is, how much headroom to leave, how to pick a standard value and a power rating, and when a resistor is the wrong tool.
Read guide →Voltage dividers and loading
The ideal divider is a ratio; the real one is a source with an output impedance. Thévenin, the ten-times rule, how ADC inputs, transistor bases and meters load a divider, choosing the resistor values, tolerance, where a divider is the wrong part, and a 12 V battery monitor worked through.
Read guide →RC filters in practice
What the time constant and the −3 dB cutoff of an RC filter mean, why 20 dB per decade is often not enough, and how the one-resistor-one-capacitor filter is used to debounce a switch, smooth a sensor, turn PWM into a voltage, and why the source and the load are part of it.
Read guide →The 555 timer in practice
What is inside the 555 and why every circuit on it times a capacitor between ⅓ and ⅔ of the supply; the astable and monostable in detail; capacitors and resistors that hold the timing; bipolar against CMOS; the traps that cost an afternoon; and where a 555 still beats a microcontroller.
Read guide →Keeping power semiconductors cool
Why the junction temperature decides a power device's life; the three thermal resistances in series from junction to air; where the watts come from; grease, pads and torque; heat sinks in still air, in an enclosure and with a fan; measuring; and when a heat sink is the wrong answer.
Read guide →Power budgeting for battery devices
Why a battery-powered device lives or dies by its average current; the shape of a wake-measure-transmit burst; the sleep floor and the parts that quietly raise it; choosing a cell for the load; regulators at microamp loads; firmware that keeps a node asleep; and measuring it.
Read guide →PCB trace width and current
A copper trace is a resistor with poor cooling: where its heat goes, the IPC-2221 curve, why an inner trace needs twice the width, the vias and terminals that limit first, voltage drop and Kelvin sense lines, copper weight and pours, and checking a finished board.
Read guide →From dev board to product
The prototype works on the bench; a product has to answer different questions. What the dev board hid, power input, inputs and outputs that survive the field, the board and its supply chain, the enclosure, firmware for a product, EMC, safety and radio approval, documentation, and the stages between.
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