{"success":true,"version":"v1","request":{"tool":"get_calculator_schema","calculator_id":"timer-555"},"result":{"entity_type":"calculator","id":"timer-555","calculator_id":"timer-555","canonical_url":"https://tttkmbb.com/engineering/timer-555","name":"555 Timer Calculator","title":"555 Timer Calculator – Astable Frequency and Duty Cycle or Monostable Pulse Width from R and C","category":"engineering","category_name":"Engineering & Automotive","tool_name":"calculate_555_timer","featured_mcp_tool":false,"description":"Computes the output frequency, period, high and low times and duty cycle of a 555 timer in astable (oscillator) mode from R1, R2 and C, or the pulse width of the monostable (one-shot) mode from R and C, using the equations of the NE555 datasheet.","use_when":"You are choosing resistor and capacitor values for a 555 oscillator, LED blinker, PWM source or one-shot pulse and need the resulting frequency, duty cycle or pulse duration.","do_not_use_when":"The circuit uses a diode across R2 or a separate control-voltage input (different timing), a CMOS 555 at very high frequency where propagation delay matters, or you need an RC filter or charging time (use rc-time-constant).","inputs":[{"name":"mode","label":"Mode","type":"enum","required":true,"values":[{"value":"astable","label":"Astable (free-running oscillator)","aliases":["oscillator","free_running"]},{"value":"monostable","label":"Monostable (one-shot pulse)","aliases":["one_shot","oneshot","timer"]}],"description":"Astable needs r1_ohms, r2_ohms and c_microfarads; monostable needs r_ohms and c_microfarads.","example":"astable"},{"name":"r1_ohms","label":"R1 (R_A)","type":"number","unit":"Ω","required":false,"max":100000000,"exclusive_min":0,"description":"Astable: resistor between VCC and the discharge pin 7, in ohms (1 kΩ = 1000). The datasheet recommends at least 1 kΩ.","example":1000},{"name":"r2_ohms","label":"R2 (R_B)","type":"number","unit":"Ω","required":false,"max":100000000,"exclusive_min":0,"description":"Astable: resistor between the discharge pin 7 and the threshold/trigger pins 6/2, in ohms.","example":10000},{"name":"c_microfarads","label":"Timing capacitor C","type":"number","unit":"µF","required":true,"max":1000000,"exclusive_min":0,"description":"Timing capacitor from pins 6/2 to ground, in microfarads (1 nF = 0.001 µF, 100 nF = 0.1 µF).","example":10},{"name":"r_ohms","label":"R (monostable)","type":"number","unit":"Ω","required":false,"max":100000000,"exclusive_min":0,"description":"Monostable: timing resistor between VCC and pins 6/7, in ohms; if omitted, r1_ohms is used.","example":100000}],"outputs":[{"name":"frequency_hz","label":"Frequency","type":"number","unit":"Hz","decimals":4,"description":"Astable output frequency 1.44 / ((R1 + 2·R2)·C)."},{"name":"period_s","label":"Period","type":"number","unit":"s","decimals":9,"description":"Astable period t_high + t_low = 0.693·(R1 + 2·R2)·C."},{"name":"time_high_s","label":"Time high","type":"number","unit":"s","decimals":9,"description":"Output-high (charging) time 0.693·(R1 + R2)·C."},{"name":"time_low_s","label":"Time low","type":"number","unit":"s","decimals":9,"description":"Output-low (discharging) time 0.693·R2·C."},{"name":"duty_cycle_percent","label":"Duty cycle","type":"number","unit":"%","decimals":2,"description":"time_high / (time_high + time_low) × 100; always above 50 % in the basic astable circuit."},{"name":"pulse_width_s","label":"Pulse width","type":"number","unit":"s","decimals":9,"description":"Monostable output pulse duration 1.1·R·C."},{"name":"period_text","label":"Period / pulse width","type":"string","decimals":4,"description":"Period (astable) or pulse width (monostable) with an SI prefix, e.g. 145.5 ms."}],"input_schema":{"type":"object","properties":{"mode":{"description":"Astable needs r1_ohms, r2_ohms and c_microfarads; monostable needs r_ohms and c_microfarads.","type":"string","enum":["astable","monostable"],"examples":["astable"]},"r1_ohms":{"description":"Astable: resistor between VCC and the discharge pin 7, in ohms (1 kΩ = 1000). The datasheet recommends at least 1 kΩ. Unit: Ω.","type":"number","maximum":100000000,"exclusiveMinimum":0,"examples":[1000],"x-unit":"Ω"},"r2_ohms":{"description":"Astable: resistor between the discharge pin 7 and the threshold/trigger pins 6/2, in ohms. Unit: Ω.","type":"number","maximum":100000000,"exclusiveMinimum":0,"examples":[10000],"x-unit":"Ω"},"c_microfarads":{"description":"Timing capacitor from pins 6/2 to ground, in microfarads (1 nF = 0.001 µF, 100 nF = 0.1 µF). Unit: µF.","type":"number","maximum":1000000,"exclusiveMinimum":0,"examples":[10],"x-unit":"µF"},"r_ohms":{"description":"Monostable: timing resistor between VCC and pins 6/7, in ohms; if omitted, r1_ohms is used. Unit: Ω.","type":"number","maximum":100000000,"exclusiveMinimum":0,"examples":[100000],"x-unit":"Ω"}},"additionalProperties":false,"required":["mode","c_microfarads"]},"output_schema":{"type":"object","properties":{"frequency_hz":{"description":"Astable output frequency 1.44 / ((R1 + 2·R2)·C). Unit: Hz.","type":"number","x-unit":"Hz"},"period_s":{"description":"Astable period t_high + t_low = 0.693·(R1 + 2·R2)·C. Unit: s.","type":"number","x-unit":"s"},"time_high_s":{"description":"Output-high (charging) time 0.693·(R1 + R2)·C. Unit: s.","type":"number","x-unit":"s"},"time_low_s":{"description":"Output-low (discharging) time 0.693·R2·C. Unit: s.","type":"number","x-unit":"s"},"duty_cycle_percent":{"description":"time_high / (time_high + time_low) × 100; always above 50 % in the basic astable circuit. Unit: %.","type":"number","x-unit":"%"},"pulse_width_s":{"description":"Monostable output pulse duration 1.1·R·C. Unit: s.","type":"number","x-unit":"s"},"period_text":{"description":"Period (astable) or pulse width (monostable) with an SI prefix, e.g. 145.5 ms.","type":"string"}}},"formula":"C = c_microfarads × 1e-6; astable: frequency_hz = 1.44 / ((r1_ohms + 2·r2_ohms)·C), time_high_s = 0.693·(r1_ohms + r2_ohms)·C, time_low_s = 0.693·r2_ohms·C, period_s = time_high_s + time_low_s, duty_cycle_percent = time_high_s / period_s × 100; monostable: pulse_width_s = 1.1·r_ohms·C","method":"Datasheet equations for the bipolar NE555 with the threshold at 2/3 VCC and trigger at 1/3 VCC (0.693 = ln 2; the frequency constant 1.44 is the datasheet's rounding of 1/0.693, so frequency × period differs from 1 by about 0.2 %). Real timing deviates by a few percent because of capacitor tolerance, leakage and the 555's internal delays; C should be at least about 1 nF and R1 at least 1 kΩ.","sources":[{"name":"Texas Instruments – NE555 precision timer datasheet (SLFS022), astable and monostable operation","url":"https://www.ti.com/lit/ds/symlink/ne555.pdf","type":"standard","retrieved_at":"2026-09-24"},{"name":"Wikipedia – 555 timer IC","url":"https://en.wikipedia.org/wiki/555_timer_IC","type":"reference","retrieved_at":"2026-09-24"}],"freshness":{"type":"static","max_age_seconds":null,"note":"Deterministic formula with fixed constants; results never go stale. Inputs supplied by the caller determine the output."},"examples":[{"name":"Astable: R1 1 kΩ, R2 10 kΩ, C 10 µF","inputs":{"mode":"astable","r1_ohms":1000,"r2_ohms":10000,"c_microfarads":10},"expected":{"frequency_hz":6.8571,"period_s":0.14553,"time_high_s":0.07623,"time_low_s":0.0693,"duty_cycle_percent":52.38,"period_text":"145.5 ms"},"url":"https://tttkmbb.com/api/v1/calculate/timer-555?mode=astable&r1_ohms=1000&r2_ohms=10000&c_microfarads=10"},{"name":"Monostable: R 100 kΩ, C 10 µF","inputs":{"mode":"monostable","r_ohms":100000,"c_microfarads":10},"expected":{"pulse_width_s":1.1,"period_text":"1.1 s"},"url":"https://tttkmbb.com/api/v1/calculate/timer-555?mode=monostable&r_ohms=100000&c_microfarads=10"}],"faq":[{"q":"How do I get a 50 % duty cycle?","a":"The basic astable always exceeds 50 % because C charges through R1 + R2 but discharges through R2 only; make R2 much larger than R1 to approach 50 %, or add a diode across R2 so the high time becomes 0.693·R1·C."},{"q":"Why does frequency × period not equal exactly 1?","a":"The datasheet rounds 1/ln 2 = 1.443 to 1.44 in the frequency formula while the high and low times use 0.693; both are reported as published, and the 0.2 % difference is far below component tolerances."},{"q":"What component ranges are practical?","a":"Keep R1 ≥ 1 kΩ (discharge-transistor current), R1 + R2 ≤ about 3.3 MΩ (bipolar 555 bias current) and C ≥ about 1 nF; the bipolar NE555 works to roughly 500 kHz, CMOS versions to a few MHz."}],"tags":["555 timer","555 astable","555 monostable","555 frequency calculator","duty cycle","one shot pulse"],"related":[{"calculator_id":"rc-time-constant","reason":"Charging behaviour of the timing capacitor through a resistor."},{"calculator_id":"op-amp-gain","reason":"Amplify or buffer the 555 output."},{"calculator_id":"lc-resonance","reason":"Alternative LC oscillator frequency."}],"links":{"html":"https://tttkmbb.com/engineering/timer-555","markdown":"https://tttkmbb.com/engineering/timer-555.md","json":"https://tttkmbb.com/engineering/timer-555.json","api":"https://tttkmbb.com/api/v1/calculate/timer-555","schema":"https://tttkmbb.com/api/v1/calculators/timer-555","openapi":"https://tttkmbb.com/openapi.json","mcp":"https://tttkmbb.com/mcp"},"version":"v1","updated_at":"2026-09-24"},"timestamp":"2026-09-24T03:44:08Z"}