Arduino Uno Voltage Divider Calculator
Calculate output voltage and Arduino ADC readings for your electronics projects.
Voltage Divider Calculator
Output Voltage vs. R2 Value
| Resistor R2 (Ohms) | Output Voltage (Vout) | Arduino ADC Reading |
|---|
This table shows how the output voltage and corresponding Arduino ADC reading change with different values for Resistor 2, assuming R1 and Vin are constant.
Vout & Current vs. R2 Resistance
This chart visualizes the relationship between Resistor 2’s value and the resulting Output Voltage (blue) and Circuit Current (green).
What is an Arduino Voltage Divider Calculator?
An Arduino Voltage Divider Calculator is a tool designed for electronics hobbyists, students, and engineers who work with Arduino microcontrollers. Its primary purpose is to calculate the output voltage from a ‘voltage divider’ circuit. This simple but crucial circuit uses two resistors to scale down a higher input voltage to a lower output voltage. For Arduino users, this is most commonly used to safely connect sensors that operate at a higher voltage than the Arduino’s input pins can handle (typically 5V or 3.3V). A good Arduino Voltage Divider Calculator also provides the corresponding digital value (from 0-1023) that the Arduino’s Analog-to-Digital Converter (ADC) will report when it reads this new voltage.
Who Should Use It?
Anyone interfacing analog sensors with an Arduino should use this tool. This includes makers building weather stations, robotics enthusiasts reading sensor data, and students learning about basic electronics and analog-to-digital conversion. If your sensor outputs a voltage range of 0-10V and your Arduino reads a maximum of 5V, this Arduino Voltage Divider Calculator is essential for designing the circuit to make them compatible.
Common Misconceptions
A common mistake is thinking a voltage divider can be used to power devices. For instance, you should not use a voltage divider to step down 9V to 5V to run another Arduino. Voltage dividers are meant for low-current signal-level applications, like reading a sensor value. They are inefficient for power delivery and the output voltage will drop significantly under load, which can damage your components. Using an Arduino Voltage Divider Calculator helps in understanding the signal level voltages, not for creating a power supply.
Arduino Voltage Divider Calculator Formula and Mathematical Explanation
The calculation is based on Ohm’s Law. A voltage divider circuit works by creating a voltage drop across two resistors in series. The output voltage (Vout) is taken from the point between the two resistors. The Arduino Voltage Divider Calculator uses the following fundamental formula:
Vout = Vin * (R2 / (R1 + R2))
Where Vin is the input voltage, R1 is the resistor connected to the input voltage, and R2 is the resistor connected to ground. The Arduino’s analog input pin reads this Vout. The Arduino then converts this analog voltage into a digital value using its 10-bit ADC. This conversion is calculated as:
ADC Value = (Vout / Vref) * 1023
Where Vref is the Arduino’s analog reference voltage, typically the same as its operating voltage (e.g., 5V). Our Arduino Voltage Divider Calculator performs both of these calculations for you.
Variables Table
| Variable | Meaning | Unit | Typical Range |
|---|---|---|---|
| Vin | Input (Source) Voltage | Volts (V) | 3.3V, 5V, 9V, 12V |
| R1 | First Resistor | Ohms (Ω) | 1 kΩ – 100 kΩ |
| R2 | Second Resistor | Ohms (Ω) | 1 kΩ – 100 kΩ |
| Vout | Output Voltage | Volts (V) | 0 – Vin |
| ADC Value | Arduino’s Digital Reading | (none) | 0 – 1023 |
Practical Examples (Real-World Use Cases)
Example 1: Reading a 12V Automotive Sensor
Imagine you want your Arduino Uno to monitor a sensor in your car that outputs a signal from 0V to 12V. Since the Arduino’s analog pin can only handle up to 5V, you need to scale this voltage down.
Inputs: Vin = 12V (maximum sensor output), Target Vout = 5V.
Goal: Choose R1 and R2 so that when the sensor outputs 12V, Vout is 5V. A common choice is to set R1 = 10 kΩ. Using the Arduino Voltage Divider Calculator or rearranging the formula, you find R2 should be around 7.14 kΩ. The closest standard resistor is 6.8 kΩ.
Result: With R1=10kΩ and R2=6.8kΩ, a 12V input gives a 4.86V output, which is safely readable by the Arduino. The calculator would show an ADC reading of approximately 995.
Example 2: Using a Photoresistor (LDR) to Detect Light
A photoresistor changes its resistance based on light levels. To measure this change, you can use it in a voltage divider. Let’s say the LDR is R2, and it ranges from 500 Ω in bright light to 200 kΩ in the dark.
Inputs: Vin = 5V, R1 = 10 kΩ (a fixed resistor).
Calculation (Bright Light): R2 = 500 Ω. Vout = 5 * (500 / (10000 + 500)) = 0.24V. ADC reading ≈ 49.
Calculation (Dark): R2 = 200 kΩ. Vout = 5 * (200000 / (10000 + 200000)) = 4.76V. ADC reading ≈ 975.
Interpretation: By reading the ADC value, your Arduino code can determine the ambient light level. This is a classic application easily modeled by an Arduino Voltage Divider Calculator.
How to Use This Arduino Voltage Divider Calculator
Using this calculator is a straightforward process designed to give you instant results for your Arduino projects.
- Enter Input Voltage (Vin): This is the highest voltage your sensor will output or the source voltage of your circuit. For many Arduino projects, this will be 5V, but it could be 9V from a battery or 12V from a power supply.
- Enter Resistor 1 (R1): This is the value in Ohms of the resistor that is connected between your input voltage source and the Arduino’s analog input pin. A value of 10,000 Ohms (10kΩ) is a common starting point.
- Enter Resistor 2 (R2): This is the value in Ohms of the resistor connected between the Arduino’s analog input pin and ground.
- Read the Results: The calculator instantly updates. The primary result is the Output Voltage (Vout), which is the voltage your Arduino will actually see. You also get the corresponding Arduino ADC Reading (0-1023), the total circuit resistance, and the current draw.
- Analyze the Table and Chart: The dynamic table and chart show how Vout changes with different R2 values, helping you understand the circuit’s behavior and choose the best components for your needs. This makes it more than just a simple Arduino Voltage Divider Calculator; it’s a design tool.
Key Factors That Affect Arduino Voltage Divider Results
- Resistor Tolerance: Resistors are not perfect. A 10kΩ resistor with a 5% tolerance could have an actual resistance anywhere between 9.5kΩ and 10.5kΩ. This variance affects the accuracy of your Vout. For precision, use resistors with 1% tolerance.
- Input Voltage Stability: The Vout is directly proportional to Vin. If your input voltage source is noisy or fluctuates, your output voltage and ADC reading will be unstable. A clean power source is crucial for accurate readings.
- Arduino’s ADC Input Impedance: The Arduino’s analog input pin has its own internal resistance (very high, but not infinite). For best results, the total resistance of your voltage divider (R1 || R2) should be 10kΩ or less. This is a key technical detail that our Arduino Voltage Divider Calculator helps you manage by showing the total resistance.
- Analog Reference (Vref) Accuracy: The ADC calculation depends on the Arduino’s reference voltage. If you power your Arduino via USB, the 5V line might actually be 4.9V or 5.1V. This slight difference will skew the final ADC value. For high accuracy, use the internal, more stable 1.1V reference voltage.
- Load on the Output: If you connect another component to the Vout point, it will draw current and change the voltage. The Arduino’s input pin draws very little current, so it’s usually not an issue, but it’s a factor to be aware of in complex circuits.
- Temperature: The resistance of most resistors changes slightly with temperature (known as the temperature coefficient). For most hobbyist projects this is negligible, but in high-precision or extreme-environment applications, it can become a factor.
Frequently Asked Questions (FAQ)
1. What is the best ratio for R1 and R2?
It depends entirely on your Vin and desired Vout. The goal is to choose a ratio R2 / (R1 + R2) that scales your maximum Vin down to just below your Arduino’s Vref (e.g., 5V). The Arduino Voltage Divider Calculator is the perfect tool for finding this ratio.
2. Why is my analogRead() value different from what the calculator predicts?
This is usually due to resistor tolerance. Your “10kΩ” resistor might actually be 9.8kΩ. Other factors include the actual Vref of your Arduino board not being exactly 5.0V. Measure your resistors with a multimeter for more accurate calculator results.
3. Can I use a voltage divider to power a motor or a servo?
No. This is a critical point. Voltage dividers are for creating a reference voltage for a high-impedance input (like an Arduino analog pin), not for delivering power. Motors draw significant current, which would cause the output voltage of the divider to collapse. Use a proper voltage regulator or motor driver instead.
4. What happens if R1 is much larger than R2?
The output voltage will be very low. The ratio R2 / (R1+R2) will be very small, so Vout will be a tiny fraction of Vin. The Arduino Voltage Divider Calculator will clearly show this relationship.
5. How do I choose the actual resistor values, not just the ratio?
A good rule of thumb is to keep the total resistance (R1 + R2) in the range of 10kΩ to 100kΩ. If it’s too low, you waste power by drawing unnecessary current. If it’s too high (over ~100kΩ), it can interact poorly with the Arduino’s input impedance, leading to inaccurate readings.
6. Does this Arduino Voltage Divider Calculator work for other microcontrollers like ESP32 or Raspberry Pi Pico?
Yes, the voltage divider principle is universal. However, you must adjust for the specific microcontroller’s Vref and ADC resolution. For an ESP32, Vref is typically 3.3V and the ADC might be 12-bit (0-4095). The Vout calculation remains the same.
7. What is “input impedance” and why does it matter?
Input impedance is the effective resistance of an input pin. The ATmega328P datasheet (the chip on the Arduino Uno) recommends that the source impedance (your voltage divider’s effective resistance) be 10kΩ or less for the most accurate ADC readings. Our Arduino Voltage Divider Calculator shows you the total resistance to help you stay within this guideline.
8. Can I use a potentiometer as a voltage divider?
Yes, a potentiometer is a variable voltage divider in a single package. It’s a resistor with a third ‘wiper’ connection that can move along the resistive material. Connecting the two outer pins to Vin and Ground, and the center wiper pin to your Arduino’s analog input, creates a perfect, adjustable voltage divider.
Related Tools and Internal Resources
Calculate voltage, current, resistance, and power with our fundamental Ohm’s Law tool.
A deep dive into how the `analogRead()` function works and how to interpret its values.
Resistor Color Code Calculator
Decode the value of your resistors using their colored bands.
Understand and calculate frequencies and duty cycles for Arduino’s PWM outputs.
Arduino Power Consumption Guide
Learn how to optimize your projects for lower power consumption.
Capacitor Charge Time Calculator
Calculate the time it takes to charge or discharge a capacitor in an RC circuit.