Self or USB Powered
A self or USB-powered system is one that draws power from a source that is not specifically designed as a power supply.
The USB (Universal Serial Bus) incorporates as part of its protocol access to the power supply of the hub or host node. It is from this source that an embedded development board can draw the voltage needed to power its circuitry, nominally.
The max voltage | max current specification for the USB bus is shown below. USB 2.0 is the older specification released in 2000, with the later specifications listed below. Most laptops and desktops are able to support USB2.0.
Specifications | Max. Voltage | Max. Current |
|---|---|---|
USB 2.0 | 5V | 500mA |
USB 3.0 / USB3.1 | 5V | 900mA |
USB Battery Charging (BC) 1.2 | 5V | 1.5A |
USB-C Current Mode (non-PD) | 5V | 3A |
While the standard may be as cited above, the issues in practice is 1) Is it a good idea to push 1/2 an amp through the USB port of a laptop, and 2) has the USB port for this particular source been designed to handle
The Radix Nano support being USB powered, and there is a jumper to configure the PCB to run in this mode. When the jumper is in place as shown below, and the PCB is connected to a PC, Laptop it will power up.
If the PCB is connected via a USB-type cable to a source that does not comply with the USB standard, this method of powering the PCB is only advised if the inbound supply is regulated to comply with the standard. It must not exceed 5Vdc.
It is a valid question what could you power with a 500mA threshold?
- You could power a variety of devices, for example, an LCD Display with one or two sensors.
- You Could not power: GSM modem, WIFI, small motor, etc
Any item with an initial or high current draw would not be able to be powered from the USB PORT.
While the USB port offers a powered connection, it is not a power source. It is available for use, however, caution should be exercised. In experimental work, the latency is always something that can be short and that can damage your Notebook or Desktop PC.
