Ohm's Law Triangle
Solve for voltage, current, resistance, or power from any two known values. Includes a watts-from-V-and-R shortcut and live unit conversion.
Open calculator
Elektro Krishna · Resources
A working library for engineers who build, test, and ship circuits & code.
Curated calculators, reference sheets, conversion tables, and downloadable guides — built from the same formulas and shortcuts we use on real projects. No fluff, no filler, just the tools we wished we'd had on day one.
01 · Tools & Calculators
Most used
Circuit
Circuit
RF & Signal
PCB Layout
Code
Pick a tool. Get an answer. Move on with your build.
These are the calculators we open most often — Ohm's law variants, RC time constants, voltage dividers, dB conversions, and a few PCB layout helpers. Each runs in your browser; nothing is sent to a server.
Resistor Divider Designer
Enter Vin, Vout, and a reference current. The tool picks the closest E24 resistor pair and shows the actual measured output and tolerance.
Open calculatorRC Time Constant (τ)
Compute the charge/discharge time constant and the %-of-Vcc reached after any duration. Useful for debounce, timing, and filter design.
Open calculatordB / Linear Converter
Convert between dBm, dBW, watts, and volts across 50 Ω and 75 Ω systems. Handy for RF, audio, and link-budget spreadsheets.
Open calculatorTrace Width & Current
IPC-2152-inspired trace width estimator. Enter current, copper weight, and allowed temperature rise to get a safe internal/external trace width.
Open calculatorBit & Byte Sizer
See how many values fit in 8/16/32/64-bit registers, signed vs. unsigned ranges, and the exact rollover point. Includes C/C++ macro snippets.
Open calculator
02 · Formulas & Cheat Sheets
The five equations you actually reach for at 11pm.
Every formula here is the one we wish we'd had pinned to the wall during our first year — explained in plain language, with a worked example, the units, and a "when to use it" note.
Ohm's Law
V = I · R ⟶ I = V ⁄ R ⟶ P = V · I
Use whenever you know two of the three and need the third. The power form (P = V·I) extends to any DC branch — multiply, don't overthink.
Vvolts
Iamps
Rohms
Pwatts
Voltage Divider
Vout = Vin · R2 ⁄ (R1 + R2)
Works for reference voltages, level shifting, and biasing. Load the output with at least 10× R2 to keep the math honest.
RC Cutoff Frequency
fc = 1 ⁄ (2π · R · C)
The −3 dB point of a first-order low-pass or high-pass filter. Aim for 5–10× the cutoff below your signal of interest for clean attenuation.
fchertz
Rohms
Cfarads
Try it: RC cutoff
Type any two values, leave the third blank.
Cutoff frequency (−3 dB)
159.15Hz
Signals at this frequency pass at ~70.7% amplitude; signals well above it attenuate at −20 dB/decade.
More cheat sheets
- Capacitor code lookup (ceramic, electrolytic, tantalum)
- SMD resistor codes (3-, 4-, and 5-digit)
- Wire gauge → amps → mm² (AWG & metric)
- Logic level voltages (TTL, CMOS 3.3/5V, LVDS)
03 · Reference Charts
Common microcontroller pin capabilities at a glance.
A condensed comparison of the specs we look up most often when picking an MCU for a new design. For deeper comparisons, see the full dataset in our articles library.
| Family | Core | Logic | ADC | GPIO drive | Best for |
|---|---|---|---|---|---|
| ATmega328P | 8-bit AVR | 5 V | 10-bit · 6 ch | 40 mA | Bench tools, simple control |
| ESP32 | Xtensa LX6 / LX7 | 3.3 V | 12-bit · 18 ch | 40 mA | Wi-Fi/BLE, IoT, sensor hubs |
| STM32F4 | 32-bit ARM Cortex-M4 | 3.3 V | 12-bit · 16 ch | 25 mA | Motor control, DSP, audio |
| RP2040 | 32-bit dual ARM M0+ | 3.3 V | 12-bit · 4 ch | 16 mA | PIO-driven protocols, low-cost |
| nRF52840 | 32-bit ARM Cortex-M4 | 3.3 V | 12-bit · 8 ch | 15 mA | Bluetooth LE, wearables |
| PIC16F1xxx | 8-bit enhanced | 5 V | 10-bit · 12 ch | 25 mA | Automotive, harsh environments |
Numbers reflect typical datasheet values. Always check the exact silicon revision you're using — drive strength and ADC specs vary by package and revision.
04 · Downloadable Guides
Take it offline. Print it. Tape it inside a project box.
Free PDFs and spreadsheets, no email required. Each one has been used on a real build, then rewritten until it was actually useful at the bench.
PDF
Bench Power Supply Setup Checklist
A one-page SOP for bringing up a new linear or switching supply — fuse, current limit, sense-lead routing, and the four measurements that catch 90% of faults.
DownloadXLS
Bill-of-Materials Cost Estimator
A pre-built spreadsheet with distributor-aware columns, alternates, and stock thresholds. Drop in your parts, get a per-board and per-batch cost in seconds.
DownloadZIP
KiCad Symbol & Footprint Starter Pack
160 hand-verified symbols and footprints for passives, common ICs, and a few favorite connectors. Drop into your project library, edit as needed.
DownloadPDF
First-Rev PCB Bring-up Workflow
An opinionated 14-step bring-up flow covering visual inspection, isolation tests, power-on procedures, and the exact order to validate rails, clocks, and I/O.
Download
05 · Questions
Asked & answered
Quick answers to the things readers ask most about the resource library — who maintains it, how to suggest a tool, and how accurate the calculators really are.
Are the calculators really running in my browser?
Yes. Every calculator is plain HTML and JavaScript — no backend, no telemetry, no data sent to a server. You can even save the page and run them offline.
Where do the formulas come from?
Standard electrical engineering references (Horowitz & Hill, the Art of Electronics, manufacturer datasheets) cross-checked against the real measurements we take on our own prototypes. The trace-width tool uses the IPC-2152 conservative curve.
Can I suggest a tool or formula to add?
Absolutely. We add new tools based on what readers ask for. Use the contact form with "Resource suggestion" in the subject — include the formula, the use case, and (if you have it) a worked example.
Do I need to create an account to download guides?
No. Every downloadable guide, spreadsheet, and library is a direct link. We may add an email-optional newsletter later, but the resources themselves will stay open.
How often is the library updated?
We push a new tool or refresh an existing one about once a week. The library's "last updated" date sits at the top of each calculator; the downloadables are versioned in their filename.
Missing a tool you keep reaching for?
If there's a calculator, chart, or template you'd find genuinely useful — tell us. We build the next one based on what readers ask for, and the best suggestions get a credit line on the published version.