Jon's Place

Sunday, January 3, 2016

Roz - Power Board

So my brother Dave and I have been designing a new power management and distribution board for Roz and his walker. Dave bought a 6-legged bioloid walker from Trossen Robotics, and we'll be sharing code and hardware on our projects.

Its very close to being sent off to the board house to get made. Here's what the schematic looks like:

Roz - Power Board Schematic

 And this is the PCB layout:

Roz - Power Board PCB

The PCB will be 80mm x 42mm. If you want to take a closer look, you can find the design files in my github account. We use Kicad for all PCB design.

This board has a number of nice features. You can plug in wall power (12 volts) and it automatically switches to use that to power the robot instead of the battery. When you unplug wall power, it automatically switches back to battery without missing a beat. It will also monitor the voltage in each cell of the battery (we use Lithium Polymer 3-cell battery packs).

The main power on/off switch is actually a push-button (which can be remotely mounted). Push and hold it for more than 500 milliseconds and the circuit powers up. Push and hold (while powered up) for more than 2 seconds and the circuit powers down. Of course, its all programmable, using the 32-bit ARM Cortex M4 chip onboard, running MicroPython (of course, what else?)

The board provides a five amp/five volt regulator, to power a raspberry pi. On Roz, I'll be using a raspberry pi 2, along with a 320 x 240 touch screen LCD panel display. Both of these were purchased from BC Robotics, and I definitely recommend them as a distributor for Pololu and Adafruit stuff if you live in Canada.

The microcontroller (an STM32F401) will also be a device on the bioloid bus, and so can be queried from the pi like the AX-12 servos. This will allow the pi to shut down power to the entire system, as well as monitor power. The microcontroller has an extra four general purpose I/O ports (which can be digital or analog), as well as an I2C port, an SPI port, and a UART. All of the ports have jumpers to allow either five volts or 3.3 volts to power whatever is plugged in.

Designing, prototyping, and building this board has been a lot of fun. I'll report back here once I get the actual bare board back from manufacturing.