Documentation sections

PWM Duty Cycle Calculator

POSThttps://rftools.io/api/py/v1/calculate

Slug pwm-duty-cycle. Calculate PWM duty cycle, frequency, average voltage, off-time, and RMS voltage from on-time and period parameters

Inputs

Send every one of these in inputs, in the units shown. Most are required: a call without one is refused (400) and costs nothing; one the calculator can do without takes the default shown. An input outside its range is still computed and flagged in the provenance.

Inputs of pwm-duty-cycle
Name	Unit	Range	Default	Description
onTimenumber	μs	at least 0.001	5	Duration the signal is high in each period
periodnumber	μs	at least 0.001	10	Total period of the PWM signal
supplyVoltagenumber	V	at least 0.1	3.3	High-level voltage of the PWM signal
timerClocknumber	MHz	0.001 … 1000	16	The clock the PWM timer counts, which sets the step of the on-time and the period
requiredBitsnumber	bits	1 … 32	8	The duty resolution the design needs: 8 bits is 256 steps

Outputs

Returned in values, by key. A value that is unbounded or undefined is null.

Outputs of pwm-duty-cycle
Field	Unit	Description
dutyCycleheadline	%	Duty Cycle
frequency	kHz	Frequency
avgVoltage	V	Average Voltage
offTime	μs	Off Time
rmsVoltage	V	RMS Voltage
periodCounts	none	The period in whole ticks of the timer clock (auto-reload + 1)
onCounts	none	The compare value: the on-time in whole ticks
dutyActual	%	M over N
frequencyActual	kHz	The timer clock over N
dutyResolution_bits	bits	log2 N: the steps one period offers the duty

Calling it

Calculate: one call, the request and response in full, and its errors.
Batch: this calculator with others, or a sweep, in one request.
Solve for a target: the value of one input that brings an output to a target.

curl -X POST https://rftools.io/api/py/v1/calculate \
  -H "X-API-Key: $RFTOOLS_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "slug": "pwm-duty-cycle",
    "inputs": {
      "onTime": 5,
      "period": 10,
      "supplyVoltage": 3.3,
      "timerClock": 16,
      "requiredBits": 8
    }
  }'

import rftools

client = rftools.Client()  # reads RFTOOLS_API_KEY, or the key `rftools login` saved

result = client.calculate("pwm-duty-cycle", {
    "onTime": 5,
    "period": 10,
    "supplyVoltage": 3.3,
    "timerClock": 16,
    "requiredBits": 8,
})
print(result.values)
print(result.warnings, result.provenance.formula_ref)

const response = await fetch("https://rftools.io/api/py/v1/calculate", {
  method: "POST",
  headers: {
    "X-API-Key": process.env.RFTOOLS_API_KEY,
    "Content-Type": "application/json",
  },
  body: JSON.stringify({
    "slug": "pwm-duty-cycle",
    "inputs": {
      "onTime": 5,
      "period": 10,
      "supplyVoltage": 3.3,
      "timerClock": 16,
      "requiredBits": 8
    }
  }),
});
console.log(response.status, await response.json());

package main

import (
	"bytes"
	"fmt"
	"io"
	"net/http"
	"os"
)

func main() {
	body := []byte(`{
	  "slug": "pwm-duty-cycle",
	  "inputs": {
	    "onTime": 5,
	    "period": 10,
	    "supplyVoltage": 3.3,
	    "timerClock": 16,
	    "requiredBits": 8
	  }
	}`)
	req, err := http.NewRequest("POST", "https://rftools.io/api/py/v1/calculate", bytes.NewReader(body))
	if err != nil {
		panic(err)
	}
	req.Header.Set("X-API-Key", os.Getenv("RFTOOLS_API_KEY"))
	req.Header.Set("Content-Type", "application/json")
	res, err := http.DefaultClient.Do(req)
	if err != nil {
		panic(err)
	}
	defer res.Body.Close()
	out, _ := io.ReadAll(res.Body)
	fmt.Println(res.Status, string(out))
}

application/json

{
  "slug": "pwm-duty-cycle",
  "values": {
    "dutyCycle": 50,
    "frequency": 100.00000000000001,
    "avgVoltage": 1.65,
    "offTime": 5,
    "rmsVoltage": 2.3334523779156067,
    "periodCounts": 160,
    "onCounts": 80,
    "dutyActual": 50,
    "frequencyActual": 100,
    "dutyResolution_bits": 7.321928094887363
  },
  "warnings": [],
  "errors": [],
  "provenance": {
    "method": "calculator:pwm-duty-cycle",
    "version": "api@3f2c1a9b04de",
    "formulaRef": null,
    "assumptions": [],
    "validRange": {
      "status": "inside",
      "bounds": {
        "onTime": {
          "min": 0.001,
          "max": null,
          "unit": "μs"
        },
        "period": {
          "min": 0.001,
          "max": null,
          "unit": "μs"
        },
        "supplyVoltage": {
          "min": 0.1,
          "max": null,
          "unit": "V"
        },
        "timerClock": {
          "min": 0.001,
          "max": 1000,
          "unit": "MHz"
        },
        "requiredBits": {
          "min": 1,
          "max": 32,
          "unit": "bits"
        }
      },
      "outside": [],
      "model": null
    },
    "computedAt": "2026-09-24T14:05:11.003Z",
    "inputs": {
      "onTime": 5,
      "period": 10,
      "supplyVoltage": 3.3,
      "timerClock": 16,
      "requiredBits": 8
    },
    "seed": null,
    "elapsedSeconds": 0.003
  }
}

{
  "detail": [
    {
      "type": "float_parsing",
      "loc": [
        "body",
        "inputs",
        "onTime"
      ],
      "msg": "Input should be a valid number, unable to parse string as a number",
      "input": "abc"
    }
  ]
}

An input sent as text. Nothing was counted.

{
  "detail": "More than 120 requests in 60 seconds from this address.",
  "errorKind": "rate_limited",
  "limit": 120,
  "windowSeconds": 60,
  "upgradeUrl": "https://rftools.io/pricing/"
}

Too many requests in a minute, with Retry-After.

Same inputs on the calculator pagePWM Duty Cycle Calculator, at these values