There are many ways to power the ArbotiX board. For stock InterbotiX kits, users will only need to worry about the 5v Power BUS anf the VIN Power BUS. This guide will discuss those as well as the ArbotiX's other power BUSes and options.
Power Ports and Regulators
This graphic below shows the different points where power can be connected to the ArbotiX-M, as well as th two on-board regulators. These will all be discused below.
5v Power BUS
The pins below are all connected to the 5v bus. These pins will share the same 5v power supply, which is ideal for powering a variety of analog and digital sensors, as well as outputs.
The power supply will be determined by the
VSEL jumper. If the jumper is set to
USB the 5v BUS will be powered from the FTDI-USB device. On the other hand if the jumper is set to
VIN, the 5v BUS will be powered through the on board 5v regulator. This regulator will take in power from the main VIN power signal, and convert it to a stable 5v supply. The regulator can take any input from 7-30v and convert it to a 5v supply.
|Power Jumper set to 'USB' for USB/FTDI Power||Power Jumper set to 'VIN' for Regulator Power|
The 5v BUS's current supply will be limited by the power supply. Most standard USB connections will supply 500ma. The on board regulator is capable of supplying 1500ma.
VIN Power BUS
The VIN Power BUS can be powered from either the blue screw terminal, or the DC jack - both are electically equivalent (with the DC jack being center-positive). The ArbotiX will accept any VIN from 7v-30v, though it is most commonly used with at 12v SMPS or a 3-cell 11.1v LiPo battery. The voltage you choose will directly power any DYNAMIXEL servos, so be careful to choose an appropriate voltage.
The VIN Power bus will supply power to the 5v regulator and the DYNAMIXEL chain regardless of the
VSEL jumper settings.
Aux. Hobby Servo Power BUS
The Aux. Hobby Servo Power BUS is supplied by the green screw terminal. The ground terminal is closest to the ISP port and the voltage terminal is closes to the mounting hole. This voltage will be supplied directly to the Voltage pin on the 3-pin port for digital pins
D12-D15. These pins are all tied to the hardware PWM pins on the ATMEGA644p and will work with the
servo.write() functions in the Arduino IDE.
This configuration is offered as an easy way to easily control hobby servos. When an approrpate voltage is supplied to the Aux. Hobby Servo Power BUS, hobby servos can be plugged directly into ports
Having these four ports on a seperate power bus is ideal for using both Hobby Servos and DYNAMIXEL servos from the same ArbotiX. Most DYNAMIXEL servos need 11-12V to opearate, however most hobby servos operate from 5-6v. Because the 5v regulator has a limited power output, it is unwise to power motors/servos from the 5v BUS. By adding another power supply it is easy to safely power hobby servos.
If you don't want to use an external power supply, you can use a regulator or a BEC to bring down the 12v input down to a lower voltage. For example, you can use the 6v BEC to power a 6v servo up to 3A.
There may be cases where you want to use these ports with standard 5v sensors. In this case the screw terminal must be tied to one of the many 5v pins on the board.
It is also possible to tie the VIN bus to the Aux. Hobby Servo Power bus for hobby servos that require a higher voltage.
Please keep in mind that this jumper will only affect the voltage pin of the 3-pin connector. The signal pin will still continue to generate a 0-5v signal no matter what is attached to the Aux. Hobby Servo Power Bus.
3.3v Power BUS
The ArbotiX has a 3.3v regulator to run an attached XBee. When not using an XBee, the 3.3v power can be reached through the highlighted xbee socket pin. This regulator only supplies 150ma of current, and devices requiring more current should use an external 3.3v voltage regulator.
The pins shown are attached directly to the ATMEGA644p. Each pin is capable of generating a 5v signal. These pins should NOT be used as power pins, and drawing to much current from these pins can damage the ATMEGA644p. Each pin is reccomended to sink/source up to 20ma of current at 5v. However each pin can sink/source more as long as the following conditions are met:
- The sum of all ports A0-A7 and D20-D23 should not exceed 100ma
- The sum of all ports D16-D19 RX0, TX0, RX1, TX1 and D12-D15 should not exceed 100ma
- The sum of all ports D0-D7 should not exceed 100ma
For more information see page 317 of the ATMEGA644p Datasheet
The pins shown are all connected to the same ground signal.