calc.engineer

Design a Pi-topology resistive attenuator pad. Given a desired attenuation in dB and characteristic impedance (default 50 ohm), computes the three resistor values for a symmetrical Pi-pad network. The Pi attenuator uses two shunt resistors (R1, R3) and one series resistor (R2). Commonly used in RF signal chains to reduce signal level while maintaining impedance match. Compare with attenuator_tee for T-pad topology.

Design a Tee-topology resistive attenuator pad. Given a desired attenuation in dB and characteristic impedance (default 50 ohm), computes the three resistor values for a symmetrical T-pad network. The Tee attenuator uses two series resistors (R1, R3) and one shunt resistor (R2). Commonly used in RF signal chains to reduce signal level while maintaining impedance match. Compare with attenuator_pi for Pi-pad topology.

Calculates how many days a battery bank can sustain loads without solar input — critical for off-grid and backup power sizing. Accounts for depth of discharge, round-trip efficiency (lithium vs lead-acid), minimum state of charge, and optional partial solar contribution during cloudy weather. Outputs autonomy in days and hours, usable capacity, and daily deficit. Use with avg_solar_contribution_pct = 0 for worst-case (no sun) scenarios, or 20-30% for realistic cloudy-day modeling. Chains from solar_sizing (battery_kwh) and solar_load_audit (daily_kwh).

Estimates battery charge time given capacity in mAh, charge current in mA, charger efficiency, and initial state of charge. Accounts for real-world charging losses (typically 80-90% efficient) to produce time in hours and minutes, energy required in Wh (at an optional voltage, default 3.7V for Li-ion), and the C-rate of the charge. Useful for solar charge controller sizing, USB charging time estimation, lead-acid float charging, and EV battery planning. The C-rate output helps verify the charge current is within safe limits (typically 0.5C-1C for Li-ion). Chain from solar_sizing charge_controller_amps to size a solar charging system end-to-end.

Calculates battery runtime and energy capacity given cell capacity in mAh, nominal voltage, and average current draw. Accounts for real-world discharge efficiency (Peukert-adjacent derating) to produce effective capacity, total energy in Wh, and runtime in hours and days. Useful for IoT sensor node planning, portable device design, UPS hold-up estimation, and solar battery bank cycling analysis. Outputs feed into solar_sizing (battery_kwh) and ups_runtime (battery_wh) for system-level calculations.

Calculate Body Mass Index (BMI) from weight and height using the WHO standard formula. Supports metric (kg/cm) and imperial (lbs/inches) units. Returns the BMI value, WHO classification (Underweight, Normal, Overweight, Obese Class I-III), and the healthy weight range for the given height. Formula: BMI = weight_kg / (height_m)^2. Useful for health screening, fitness planning, and clinical intake forms.

Calculates RC capacitor charge timing, energy storage, and transient voltages. Given resistance, capacitance, supply voltage, and optional initial voltage, computes the RC time constant (τ = R×C), time to reach standard charge thresholds (63%, 86%, 95%, 99%), voltage at key time points, energy stored (E = ½CV²), and peak charging current. Optionally calculates time to reach a specific target voltage using t = -τ × ln((Vsupply - Vtarget) / (Vsupply - Vinitial)). Essential for timing circuits, power-on reset delays, debounce networks, and soft-start designs. Chain from rc_filter for frequency-domain analysis or timer_555 for oscillator timing.

Estimates Meshtastic or LoRa mesh channel utilization percentage based on node count, message rate, and per-packet airtime. Determines how much of the shared radio channel is occupied and computes the maximum number of nodes before exceeding a configurable duty cycle limit (default 10%). Returns utilization percentage, headroom, and total packet count. Chain from lora_airtime to get airtime_ms input. Essential for Meshtastic mesh deployment planning to avoid channel congestion and packet collisions.

Calculate the circumference and area of a circle given either a radius or diameter. Provide one or both; if both are given, radius takes precedence. Returns circumference (C = 2πr), area (A = πr²), and both radius and diameter for completeness. Common in mechanical engineering (pulley systems, pipe sizing), electronics (antenna loop calculations, coil winding), civil engineering (manhole covers, circular foundations), and everyday measurement tasks.

Calculates compound interest growth over time using the formula A = P(1 + r/n)^(nt). Given a principal, annual rate, duration in years, and compounding frequency, returns the future value, total interest earned, effective annual rate (APY), and a year-by-year growth schedule. Supports optional recurring monthly contributions for savings projections. Works for savings accounts, CDs, investment returns, and retirement planning. Currency-agnostic.

Calculate the confidence interval for a sample mean. Given a sample mean, sample size, standard deviation, and confidence level, computes the margin of error, lower and upper bounds, critical z-score, and standard error. Supports finite population correction (FPC) when a population size is provided, which narrows the interval for samples that are a large fraction of the population. Uses the Abramowitz & Stegun rational approximation for the inverse normal CDF to derive the critical z-value. Common in survey analysis, A/B testing, and quality control.

Estimate the cooling load (BTU/hr) for a homelab or server closet based on equipment wattage, room dimensions, insulation quality, and solar exposure. All electrical power converts to heat — this tool calculates equipment heat output, envelope heat gain through walls, and solar gain to produce a total BTU/hr cooling requirement. Recommends AC tonnage, mini-split sizing (rounded to standard 6K BTU increments), and exhaust fan CFM for ventilation-only cooling. Use after power_cost to size cooling for your homelab room.

Calculate the difference between two dates in days, weeks, months, years, and business days. Accepts dates in YYYY-MM-DD format. Returns the absolute difference (order doesn't matter) plus a flag indicating whether the end date is in the future relative to start. Business days count only Monday through Friday. Useful for project planning, deadline tracking, contract duration calculations, and age computations.

Convert a power level in dBm to milliwatts, watts, dBW, and RMS voltage across a given impedance. dBm is the standard unit for RF power referenced to 1 milliwatt. This tool is essential when interfacing datasheets (which use dBm) with circuit analysis (which uses volts and watts). Default impedance is 50 ohms, matching most RF systems. Use this to quickly verify power amplifier output, receiver sensitivity, or regulatory EIRP limits.

Calculate physical dimensions of a dipole antenna for a given frequency. Returns half-wave or quarter-wave element length in metres, feet, and inches. A half-wave dipole is the most common resonant antenna with approximately 2.15 dBi gain. A quarter-wave monopole (ground plane antenna) is half the length and is widely used in handheld radios and vehicle-mounted systems. Use this before building or purchasing an antenna to verify element length for your operating frequency.

Calculates LoRa duty cycle budget for EU868, US915, AS923, and AU915 regulatory regions. Computes maximum messages per hour, minimum transmission interval, and effective data rate under regional duty cycle constraints. EU868 and AS923 enforce 1% duty cycle (ETSI); US915 has no duty cycle limit but a 400 ms dwell time per channel (FCC); AU915 has no duty cycle limit. Flags dwell-time-limited regions where packet airtime must not exceed the dwell time. Chain from lora_airtime to get airtime_ms input for end-to-end regulatory compliance analysis.

Checks EIRP (Effective Isotropic Radiated Power) compliance against regional regulatory limits for LoRa and Meshtastic operation. Computes EIRP from transmit power, antenna gain, and cable loss, then compares against FCC (US, 36 dBm), ETSI (EU, 16.15 dBm), ACMA (Australia, 30 dBm), IC (Canada, 36 dBm), and ARIB (Japan, 13 dBm) limits. Returns compliance status, margin in dB, and a warning message if over the limit. Critical for Meshtastic deployments using aftermarket high-gain antennas which can easily exceed ETSI/JP limits. Accepts tx_power and antenna_gain from meshtastic_range for chain validation.

Compute the result of raising a base to an exponent (base^exponent). Handles positive and negative exponents, fractional exponents, and zero. Returns the numeric result and a scientific notation string for very large or very small results. Useful for compound interest calculations, exponential growth/decay models, physics power laws, and combinatorics. The inverse of log_calc; chain with scientific_notation for formatted display of extreme values.

Calculate the Fresnel zone radius at the midpoint of a radio link. Given frequency in MHz, link distance in kilometres, and zone number (1-5), returns the Fresnel zone radius in metres and feet, plus the 60% clearance threshold used in practical link engineering. The first Fresnel zone defines the region where most RF energy travels; obstructions within 60% of this radius cause significant signal degradation. Feeds into link_budget for path clearance analysis.

Calculate free-space path loss (FSPL) in decibels using the ITU-R P.525 standard formula. Given a frequency in MHz and distance in kilometres, returns the expected signal attenuation in an ideal line-of-sight radio link with no obstacles, reflections, or atmospheric absorption. Also computes the RF wavelength. Use this to estimate baseline path loss before adding fade margins, antenna gains, or environmental corrections. Feeds directly into link_budget for full end-to-end analysis.

Compares total cost of ownership between a fuel generator and a solar+battery system over a configurable time horizon. Calculates yearly and cumulative costs for generator-only, solar-only (amortized), and hybrid scenarios. Accounts for fuel cost, generator consumption rate, maintenance intervals, solar system amortization, and battery coverage. Outputs yearly costs, total savings, breakeven year, solar coverage percentage, and generator hours saved. Essential for off-grid site planning, remote telecom towers, construction sites, and rural electrification proposals.

Analyze a forced-convection fin-array heatsink using established channel-flow correlations (developing laminar Nusselt, fin efficiency tanh(mH)/mH, parallel-plate friction). Computes base-to-air thermal resistance, pressure drop, base and fin-tip temperatures, fin efficiency, and the optimal fin spacing for the given airflow. Use for heatsink selection and first-pass optimization in electronics cooling. Runs instantly in-worker; mesh-level CFD via container backend is planned.

Convert numbers between hexadecimal, binary, decimal, and octal bases. Accepts any base as input (prefix 0x for hex, 0b for binary, 0o for octal, or plain decimal) and returns all four representations simultaneously. Also reports bit width, byte count, ASCII character (if printable), and signed interpretations (8-bit, 16-bit, 32-bit two's complement). Essential for embedded programming, register debugging, network protocol analysis, and color code conversion. Example: 0xFF → decimal 255, binary 0b11111111, octal 0o377, 8 bits, 1 byte.

Designs an L-network impedance matching circuit between two real impedances at a given frequency. Computes the required shunt and series reactive components (inductor and capacitor) to transform the source impedance to the load impedance. The network Q factor is sqrt(Rh/Rl - 1) where Rh is the higher impedance. Topology is automatically selected: the shunt element is placed across the higher impedance side. Essential for antenna matching, amplifier input/output matching, and maximizing power transfer. Chain from lc_resonance to match at a tank circuit's resonant frequency.

Size a DC-to-AC inverter for off-grid solar, battery backup, or mobile power systems. Computes the required continuous VA rating from total load watts and power factor, estimates surge capacity for motor-starting loads (3-7x rated power), applies NEC-recommended 20% derating for continuous operation, and selects the nearest standard inverter size. Also calculates DC input current at the system voltage for cable and fuse sizing. Chain from solar_load_audit to get peak_watts and largest_load_watts, then chain to wire_gauge or wire_ampacity to size the DC cables. Essential for off-grid cabins, RV/van builds, emergency backup, and solar+battery installations.

Calculates the resonant frequency of an LC circuit, along with optional Q factor and bandwidth when series resistance is provided. The resonant frequency f0 = 1/(2*pi*sqrt(L*C)) is where inductive and capacitive reactances cancel. Used for designing tank circuits, oscillators, bandpass filters, and antenna matching networks. If resistance R is given, computes quality factor Q = (1/R)*sqrt(L/C) and 3 dB bandwidth = f0/Q. Chain into impedance_match to design matching networks at the resonant frequency.

Calculates the current-limiting resistor for driving one or more LEDs in series from a DC supply. Computes the exact resistance from R = (Vsupply - n*Vf) / I, then selects the nearest E24 standard resistor value. Reports the actual current with the standard resistor, power dissipation, and voltage across the resistor. Supports series LED strings by specifying led_count. Validates that supply voltage exceeds total forward voltage. Chain from ohms_law for power budgeting or into trace_width for PCB layout.

Compute a full RF link budget from transmitter power, frequency, distance, and antenna gains. Calculates EIRP, free-space path loss (ITU-R P.525), received power at the receiver, and link margin relative to an optional receiver sensitivity threshold. Use this to determine whether a wireless link closes with adequate margin. Accepts output from noise_figure_cascade and feeds into snr_margin for full receive-chain analysis.

Computes a full loan amortization schedule given principal, annual interest rate, and term in months. Returns the fixed monthly payment, total interest, total payments, and a month-by-month breakdown of principal vs interest. Supports optional extra monthly payments — shows months saved and interest saved. Works for mortgages (30yr/15yr), auto loans, personal loans, and student loans. All currency-agnostic. Use with /run?page=1&page_size=12 to paginate the schedule array for context-friendly agent consumption.

Compute logarithms of a positive number in any base. Returns the custom-base logarithm, natural logarithm (ln), common logarithm (log10), and binary logarithm (log2). Useful for signal processing (decibel calculations), information theory (entropy in bits), pH chemistry, and general scientific computation. Uses the change-of-base formula log_b(x) = ln(x) / ln(b). Feeds into exponent_calc for inverse operations and scientific_notation for order-of-magnitude analysis.

Calculates LoRa packet time-on-air using the Semtech AN1200.13 formula. Computes symbol duration, preamble time, payload symbol count, effective data rate, and the minimum transmission interval for 1% duty cycle compliance. Essential for capacity planning in LoRaWAN and Meshtastic mesh networks. Accepts spreading factor (SF7-SF12), bandwidth (125/250/500 kHz), coding rate (4/5-4/8), payload size, header mode, CRC, and optional low data rate optimization. Feeds airtime_ms to channel_utilization for mesh load analysis.

Recommends optimal LoRa spreading factor, bandwidth, and TX power based on target range, terrain, and optimization priority. Iterates through all SF (7-12) and BW (125/250/500 kHz) combinations, computing achievable range, airtime, data rate, and battery impact for each. Ranks candidates by priority: 'range' maximizes distance, 'speed' minimizes airtime, 'battery' minimizes power consumption, 'balanced' penalizes extremes. Respects regional TX power limits (FCC/ETSI/ACMA) and duty cycle constraints. Returns the recommended parameters with estimated range, airtime, duty-cycle message limit, battery life, and data rate. Essential for tuning Meshtastic and LoRa deployments to specific requirements.

Estimates LoRa maximum communication range by computing the free-space path loss (FSPL) link budget and applying terrain-dependent correction factors. Calculates total link budget from transmit power, antenna gains, and receiver sensitivity, then solves the FSPL equation for distance after subtracting terrain losses (0 dB open to 50 dB indoor). Returns estimated range in km, link margin at 1 km, and effective path loss. Useful for Meshtastic deployment planning and coverage mapping. Terrain corrections are empirical estimates; real-world range varies with elevation, foliage, and weather.

Calculates LoRa receiver sensitivity from spreading factor, bandwidth, and noise figure using the Semtech SX1276 datasheet SNR thresholds. Computes the noise floor from thermal noise density (-174 dBm/Hz), channel bandwidth, and receiver noise figure, then adds the spreading-factor-dependent minimum demodulation SNR. Returns sensitivity in dBm, noise floor, required SNR, and thermal noise reference. Essential for link budget planning in LoRaWAN and Meshtastic networks. Feeds sensitivity_dbm to link_budget and lora_range_estimate for end-to-end coverage analysis.

Converts battery capacity from milliamp-hours (mAh) to watt-hours (Wh), kilowatt-hours (kWh), and joules (J) given the nominal cell voltage. This is the most common battery unit conversion needed when comparing cells rated in mAh (e.g. 18650, AA) against energy budgets specified in Wh. Essential for airline lithium battery compliance (100 Wh limit for carry-on), solar battery bank sizing, and UPS capacity planning. Echoes back input values for easy chaining into battery_life, solar_sizing, and ups_runtime tools.

Calculates Meshtastic node power consumption and battery runtime using device-specific power profiles and firmware role-based duty cycling. Models sleep, RX, and TX current draw for Heltec V3, RAK WisBlock, T-Beam, T-Beam Supreme, and Station G2 with GPS, BLE, and display peripheral toggles. Role selection (client, router, repeater, client_muted) controls the duty cycle model: routers stay in RX mode continuously while clients sleep between events. Returns average current, runtime in hours/days, daily Wh consumption, and time distribution across TX/RX/sleep states. Feed daily_wh to solar_sizing for off-grid planning.

Estimates Meshtastic node communication range using real hardware profiles and firmware channel presets. Combines device-specific TX power and antenna gain (Heltec V3, RAK WisBlock, T-Beam, T-Beam Supreme, Station G2) with firmware modem presets (Long Fast, Long Slow, Very Long Slow, Medium, Short) to compute receiver sensitivity and FSPL-based range with terrain correction. Automatically populates LoRa parameters from device and channel selection, with optional overrides for custom antennas or power levels. Essential for Meshtastic deployment planning and node placement. Returns range, sensitivity, link budget, and the effective radio parameters used.

Calculate PCB microstrip trace width for a target characteristic impedance using the Hammerstad-Jensen closed-form equations. Given target impedance (Z0), substrate dielectric constant (er), substrate height, and copper weight, returns the required trace width and effective dielectric constant. Optionally computes effective wavelength at a given frequency. Essential for RF PCB layout to achieve controlled impedance traces (e.g. 50 ohm for SMA connectors). References IPC-2141.