USB Power Connectors can provide a standardized approach for powering small projects.
Usually, when we are developing Arduino or NodeMCU-based projects on the breadboard, we rely on a USB connection for both programming and power. On the programming side, the USB connection runs through a serial communications converter. We program the MCU over a serial or COM port connection. On the power side, USB provides 5 volts to the Arduino or NodeMCU.
In many cases, the amount of power provided by the USB cable is sufficient to run the MCU as well as all of the other devices or circuits on the breadboard. If not, we need run the project off a separate power supply.
Up until now, I have been running my finished projects off an external power supply. Typically, these are “wall warts” with barrel or coaxial plugs. Usually it is a regulated power supply at 5 to 12 Volts. If I need 3.3V I can add a regulator on the PCB for that.
Many people just continue to use the USB cable for power only after the project is completed. This will work fine. Most of the USB-to-serial converters are configured to draw up to 500 ma from the computer or USB power supply.
To make things easier, you can buy various USB breakout boards, shown above. These boards bring out the USB 5 volt and ground lines into standard 0.1″ spacing. You can then use pin headers or other means to attach these to your project PCB. In some cases, these USB Power Connectors are mounted at right angles to the breakout. These boards are available from various sources including Adafruit, Sparkfun, and of course e-BAY.
USB Power Connectors – Check your Current Needs
By design, USB connections to your PC initially supply up to 100 ma for USB 2.0 and up to 150 ma for USB 3.0. However, the USB control chip can negotiate up to five times this amount (500 ma) in USB 2.0 and up to six times (900 ma) in USB 3.0. However, if you are just using a “dumb” breakout board to source power, you are limited to one unit load of 100 or 150 ma respectively. By comparison, an Arduino UNO can handle up to 200 ma through its internal regulator.
On the other hand, if you power your project through a USB cable to an external power supply (wall wart) you can easily draw up to 5 amps, depending on the power supply rating. But don’t try to power everything through the Arduino voltage regulator. As I said, that is limited to 150-200 ma.
Of course, this all only works if your project just requires 5 volts or less. If you need 12 volts, USB power connectors are not the solution.