Calculator inputs
Example data table
These examples show typical scaling cases for logic pins and ADC inputs.
| Vin (V) | R1 (Ω) | R2 (Ω) | Load (Ω) | Ideal Vout (V) | Loaded Vout (V) | Use case |
|---|---|---|---|---|---|---|
| 5 | 5,100 | 10,000 | 1,000,000 | 3.311 | 3.300 | 5 V to 3.3 V sensing |
| 12 | 27,000 | 10,000 | 1,000,000 | 3.243 | 3.220 | 12 V battery monitor |
| 24 | 100,000 | 18,000 | 2,000,000 | 3.661 | 3.634 | 24 V industrial status input |
Formula used
Ideal output voltage
Vout = Vin × R2 ÷ (R1 + R2)
Loaded lower branch resistance
Rlower(effective) = R2 || Rload = 1 ÷ (1 ÷ R2 + 1 ÷ Rload)
Loaded output voltage
Vout(loaded) = Vin × Rlower(effective) ÷ (R1 + Rlower(effective))
ADC code estimate
Code = round[(Vout ÷ Vref) × (2bits − 1)] with clamping at full scale
The calculator also estimates source current, resistor power, Thévenin resistance, tolerance spread, and logic state using your digital thresholds.
How to use this calculator
- Choose whether you want to calculate output directly or solve for one resistor.
- Enter the source voltage and the known resistor values or target output.
- Add load resistance when a digital input, ADC pin, or external circuit draws current.
- Set tolerance to preview minimum and maximum output caused by resistor variation.
- Enter ADC reference and resolution if you want a direct digital code estimate.
- Optionally provide VIL(max) and VIH(min) to classify the divider output as low, high, or undefined.
- Press Calculate divider to show the result block above the form.
- Use the CSV and PDF buttons to export the computed summary for reports or design reviews.
FAQs
1) What does a digital voltage divider do?
It scales a higher voltage to a lower, safer level for a microcontroller pin, ADC input, logic gate, or monitoring circuit without active amplification.
2) Why is loaded output different from ideal output?
The connected input is not perfectly open. Its finite resistance forms a parallel path with R2, lowering the effective bottom resistance and slightly reducing output voltage.
3) When should I use lower resistor values?
Lower values reduce sensitivity to leakage, noise, and ADC sampling effects. They also increase current draw, so choose a balance between stability and power consumption.
4) What is Thévenin resistance and why is it useful?
Thévenin resistance is the divider’s output resistance seen by the load. Lower values usually help ADC sampling and improve immunity to leakage and interference.
5) Can I use this for ADC protection?
It helps scale input voltage, but proper protection may still require clamps, series resistance, filtering, or surge protection when signals are noisy or fault-prone.
6) Why does the calculator show a tolerance range?
Real resistors vary from nominal values. The range estimates how output may shift when both divider resistors move within their stated tolerance limits.
7) What if the logic state is undefined?
Undefined means the output lies between your low and high thresholds. Adjust resistor values, add buffering, or review thresholds for reliable switching.
8) Can the calculator solve for a missing resistor?
Yes. Select the appropriate mode to solve for R1 or R2 using the target output, source voltage, and optional load resistance.