If you’re using an Arduino to control LEDs, servos, motors that run on a different voltage (e.g. 5V or 12V) or require high current (e.g. > 40mA), you'll have mixed voltage circuits. Read on to learn how to use a single power source to power your mixed voltage circuits.
Powering Arduino when accessories requires 7-12V
Connect your 7-12V power source to your Arduino using a 2.1mm DC Barrel Plug to Alligator clips or male 2.1mm plug to screw terminal block. The Arduino Uno's DC power jack accepts 7-12V and internally uses a voltage regulator to convert it voltages used in the circuits. I have a few extras from a previous project that I can loan out.
Powering Arduino when accessories require exactly 5V
Instead of using the DC power jack, cut up a USB cable and connect the 5V and GND wires in the cable to the 5V and GND wires of your power supply. (If 5V is supplied to the DC power jack on Arduino, the Arduino's 5V pins may actually be less than five volts and the board may be unstable. This voltage is too low the Arduino's internal voltage regulator to operate.)
Powering the Arduino when accessories require >12V
You'll need to use DC voltage regulator to convert the >12V used by accessories to a lower voltage that can be safely supplied to Arduino's DC power jack. The Arduino's internal linear voltage regulator overheats and can damage the board when supplied with >12V.
Powering the Arduino when accessories require < 7V but not 5V (ex: 3.3V)
Using a 7-12V power source to power your Arduino directly using the DC power jack and a switching DC step down regulator to power your accessories is recommended. (If Arduino is supplied with less than 7V, the 5V pin may actually be less than five volts and the board may be unstable.)
DC voltage regulators
There are 2 main types of DC voltage regulators used to convert between DC voltages: a switching regulator (also known as “buck converter”) is more energy efficient (>90% efficiency). A linear regulator is cheaper but less energy efficient. The Arduino Uno uses a built-in linear regulator used to convert 7-12V supplied to 5V and 3.3V used in the internal circuitry.
$7 buck converter module (Amazon)
Below are a few example parts I found for converting DC voltages.
- This $10 wire with built-in buck converter (Adafruit) outputs 5V @ up to 3A when supplied with 6V-32V.
- This $15 step down switching DC regulator chip (Adafruit) outputs 5V @ up to 1A when supplied with 6.5V-32V.
- This $7 buck converter module (Amazon) has adjustable output between 1.5-35V when supplied with 3V-40V.
- While this $2 DC inverting switching regulator (SparkFun) may be tempting due to low cost, designing a functioning circuit is probably graduate-level electrical engineering challenge, requiring calculating values of external resistors, capacitors, and inductors. If you're knowledgable about electronics, there's a 37 minute YouTube video explaining this.
Prototyping with AC wall adapter
Before using a battery, prototype your circuit first using a AC wall adapter. Choose a AC wall adapter with the exact same voltage needed and same or higher current rating needed. (Add up the current draw (typically in mA) to calculate the total current used in your circuit.)
Connect your 7-12V power source to your Arduino using a 2.1mm DC Barrel Plug to Alligator clips or male 2.1mm plug to screw terminal block.
2.1mm DC Barrel Plug to Alligator clips
Adafruit has a small selection of AC wall adapters, and RE-PC Seattle store near stadiums carries recycled AC wall adapters for $1.95.
Battery types
| Voltage | Battery type |
| 3.7V | Single cell rechargeable Lithium Ion Polymer (LiPo) battery (varies from 500mAh to 10,000mAh) |
| 4.8V | 4x NiMH rechargeable AA batteries (1000mAh to 2000mAh) |
| 6V | 2x CR2032 coin cell battery (200mAh) or 4x Alkaline AA batteries (~2700mAh) |
| 7.2V | 4x NiMH rechargeable AA batteries (1000mAh to 2000mAh) or NiMH battery packs (varies) |
| 7.4V | 2 cell rechargeable Lithium Ion Polymer (LiPo) battery (varies from 500mAh to 10,000mAh) |
| 9V | 9V battery (~500mAh) or 6x Alkaline AA batteries (1000mAh to 2000mAh) |
| 11.1V | 3 cell rechargeable Lithium Ion Polymer (LiPo) battery (varies from 500mAh to 10,000mAh) |
| 12V | 8x Alkaline AA batteries (~2700mAh) |
Battery storage capacity is measured in milliamp-hours (mAh). Higher mAh ratings for the same battery type will generally mean longer run times. A battery with a capacity rating of 1800 mAh could deliver a current of 1800mA for one hour. For reference, a typical 9V battery with 500mAh capacity powers just the Arduino for about 4 hours.
Adafruit has a nice selection of AA battery holders that hold 4, 6, or 8 AA batteries.
4x AA battery holder with on/off switch (Adafruit)
For more information on rechargeable batteries, see http://learn.adafruit.com/li-ion-and-lipoly-batteries/overview and http://www.horizonhobby.com/article/2106-understanding-rc-batteries. Battery packs can be purchased from hobby stores that carry radio control accessories such as Horizon Hobby and Hobby Lobby.
(Note: I am not affiliated with any companies mentioned here and don’t receive any compensation from them.)