KEMI Docs
Reference Library
Technical documents written by KEMI from real design, fabrication and assembly work. The articles answer questions that come up on real jobs; the reference sheets are table-and-formula lookups.
Practical Articles
How to Read Resistor Color Codes
4-, 5- and 6-band codes, reading direction, gold and silver bands, choosing E12/E24/E96 values, confirming with a meter
SMD Resistor and Capacitor Markings
Reading 103, 1002, 4R7 and 01C · why MLCCs are unmarked · the tantalum polarity trap · power and voltage by size
Choosing an LED Resistor
Worst-case math with Vf spread and supply tolerance · resistor derating · why not parallel LEDs · when to go constant-current
Voltage Divider Mistakes
Thevenin resistance and loading · ADC sampling capacitors and leakage · battery-sense drain and switched dividers · why a divider is not a supply
PCB Trace Width for Current
IPC-2221 vs IPC-2152 · copper weight · heating vs voltage drop · via current · high-current layout tips
Ordering a Controlled Impedance PCB
When you need 50/90/100 Ω · stack-up before width · coupons, TDR and ±10% · fab notes to include
Wire Gauge Selection
AWG vs mm² with resistance per foot · when voltage drop sets the gauge · round-trip length · crimp terminal ranges · CCA trap
Battery Life and Low-Power Design
Average-current math · where sleep current dominates · hidden currents like LDO Iq · self-discharge and cold · measuring with a profiler
PCB Thermal Design
Rise = power × θJA · θ vs copper area table · thermal via count and size · 2oz and MCPCB options
Silkscreen Rules
Fab minimums (0.15 mm line, 1.0 mm text) · why silk on pads is clipped · polarity and pin-1 marks · designator rules
ESD Protection Design
Which pins · three TVS numbers (VRWM, VC, CJ) · within 5 mm of the connector · values per interface
PCB Panelization
V-cut for straight edges, tabs for irregular · web and gap specs · rails, fiducials and tooling holes for SMT
Connector Selection Guide
JST, headers, terminal blocks and USB-C compared · current vs AWG · mis-insertion prevention · ordering mistakes
SLA vs FDM
Six-criteria comparison · verdicts for enclosures, gears, jigs and show models · wall, hole and support rules
Gerber Files Explained
Layer roles by extension · why drill files are separate · the pre-order checklist
Top 7 PCB Ordering Mistakes
Layer mismatch, missing outline, drill units, closed mask — and how to avoid a respin
Preparing for SMT Assembly
The six required BOM columns, CPL conventions, polarity marks and DNP notation
Reading Package Size Codes
0603 and 1608 are the same part (and not) — the conversion table and notation rules
Via Types and How to Choose
Through, blind, buried and via-in-pad · customary sizes · via treatment options
Two Layers or Four?
What forces more layers, surviving on two, and when controlled impedance starts
Decoupling Capacitor Placement
Why right at the power pin, why 100nF, and the mistakes reviews actually catch
LDO vs Buck Converter
The first fork in power design — decided with thermal math, not intuition
Preparing STL Files for Printing
Units, manifold geometry, fit tolerances and designing with supports in mind
From Schematic to PCB
What a netlist carries, footprint accidents, and why pin count measures layout effort
Reference Sheets
Excerpts from KEMI's printable reference sheets. Tables and formulas are transcribed as published; the full PDF edition is linked at the bottom of each document.
Electronics Basics
Resistor color code · Ohm's law & power formulas · capacitor marking codes
Circuit Design Reference
Pull-up/pull-down & open collector · 78XX/79XX regulators · NE555 timer circuits
FDM 3D Printing in Practice
Filament comparison matrix · nozzle size & layer height · fixing stringing in order
PCB Design Basics
Layer stack-up · trace width & current (IPC-2221) · via dimensions and selection
Notes
- · All documents are excerpts of KEMI's own work and are free to read for personal study and education.
- · Figures and formulas follow the source sheets at the time of excerpting. For real designs, part datasheets and manufacturer specs take precedence.
- · The full PDF editions (with worksheets and practice sheets) are available via the links at the bottom of each document.