---
title: "Calculates timing parameters for the ubiquitous NE555 / LM555 timer IC in astable (free-running oscillator) and monostable (one-shot pulse) modes. In astable mode, computes frequency, period, duty cycle, and HIGH/LOW durations from R1, R2, and C using f = 1.44 / ((R1 + 2·R2) · C). In monostable mode, computes pulse width from R and C using t = 1.1 · R · C. Standard 555 astable duty cycle is always >50%; for 50% duty cycle use a diode across R2. Useful for generating clock signals, PWM, delays, and debounce circuits. Chain from ohms_law for power calculations or resistor_color_code for component selection."
method: POST
path: "/api/timer_555"
tags: ["pcb"]
---

# Calculates timing parameters for the ubiquitous NE555 / LM555 timer IC in astable (free-running oscillator) and monostable (one-shot pulse) modes. In astable mode, computes frequency, period, duty cycle, and HIGH/LOW durations from R1, R2, and C using f = 1.44 / ((R1 + 2·R2) · C). In monostable mode, computes pulse width from R and C using t = 1.1 · R · C. Standard 555 astable duty cycle is always >50%; for 50% duty cycle use a diode across R2. Useful for generating clock signals, PWM, delays, and debounce circuits. Chain from ohms_law for power calculations or resistor_color_code for component selection.

`POST /api/timer_555`

## Request

- Base URL: `https://calc.engineer`
- URL: `https://calc.engineer/api/timer_555`
- Auth: none declared

## Request body

- object
  - `mode` 'astable' | 'monostable', required: Operating mode. 'astable' produces a continuous square wave. 'monostable' produces a single timed pulse.
  - `r1_ohm` number, required: Resistance R1 in ohms. In astable mode this is the charge-path resistor between Vcc and the discharge pin. In monostable mode this is the timing resistor.
  - `r2_ohm` number: Resistance R2 in ohms (astable mode only). Charge/discharge resistor between the discharge and threshold pins. Required for astable mode.
  - `c_farad` number, required: Timing capacitor in farads. Typical values range from 1 pF to 1000 µF. Use scientific notation, e.g. 1e-6 for 1 µF.

## Response `200`

Computed result for timer_555

- object
  - `result` object, required
    - `mode` string, required: Operating mode used for calculation.
    - `frequency_hz` number, nullable, required: Output frequency in Hz (astable only, null for monostable).
    - `period_s` number, nullable, required: Total period in seconds (astable only, null for monostable).
    - `duty_cycle_pct` number, nullable, required: Duty cycle as a percentage (astable only, null for monostable). Always > 50% for standard 555.
    - `time_high_s` number, required: Output HIGH duration in seconds. In astable this is the charge time; in monostable this is the pulse width.
    - `time_low_s` number, nullable, required: Output LOW duration in seconds (astable only, null for monostable).
    - `r1_ohm` number, required: R1 value used in ohms.
    - `r2_ohm` number, nullable, required: R2 value used in ohms (null for monostable).
    - `c_farad` number, required: Capacitor value used in farads.
    - `c_display` string, required: Human-readable capacitor value string (e.g. '100 nF', '4.7 µF').
  - `tool` string, required
  - `version` string, required
  - `computed_at` string, date-time, required
  - `chain` object, required
    - `feeds` unknown[]
      - unknown
    - `accepts_from` unknown[]
      - unknown

## Other responses

- `400`: Validation error or invalid JSON
- `404`: Tool not found

---

[API](https://skmtc.dev/calc/apis/calc-engineer-api.md) · [All operations](https://skmtc.dev/calc/apis/calc-engineer-api/llms.txt) · [OpenAPI document](https://skmtc.dev/calc/apis/calc-engineer-api/revisions/8830480ec488?raw)