Jun 17, 2014

Back in Black - a DIY raspberry pi Boombox: Wire it Up - Power


The BinB boombox has a different power setup from the prototype - it can be battery powered or AC powered. If you want to run the boombox often on battery, the recommended choice is an SLA (Sealed Lead Acid) battery of good quality. These will usually add about 5 lbs/2.3kg to the boombox, and cost about $20USD and up, depending on amp hours.

Since I was  going to use a battery only for short demonstrations, I bought a cheap one from ebay:
Later, I found out these are of poor quality and can even be dangerous in some circumstances.  Not recommended! See the forum thread at dvxuser.

Here's my original diagram (on a napkin!) for the power distribution scheme:

  • PB = OSH Latching Push-button Switch, in-line to +V
    • NC = Normally Closed; and of course, by NC I really meant NO, Normally Open terminal
    • C    = Common 
    • LiPo +V and Wall +V are tied together with the C terminal of the Push-button switch; NO is tied to the +12V rail of the distribution circuit board
    • When the Push-button is latched, +12V flows to circuit board
  • DC In = 2.1 mm jack
    • with the center positive plug inserted, the "switched" negative terminal is cut out of the circuit; the LiPo battery negative/GND is attached to the switched terminal, so it's cut out of the circuit when attaching to wall power
    • the other negative/GND (-) terminal is always attached to the circuit
  • LiPo Battery is attached via another DC 2.1mm jack
  • PB LED = LED internal to the OSH Switch (with built-in resistor), powered when PB is latched "on"
  • UBEC = Universal Battery Elimination Circuit, a Buck Converter for down converting from 12v to 5v
    • Amp for speakers is fed from 12V rails
    • USB hub is fed from 5V rails
      • raspberry pi powered from USB hub
      • Arduino powered from USB hub
NOTE: The UBEC is wired between the 12V and 5V rails; the drawing makes the rails look like they are tied together. NO! Don't tie the rails together!

Here's are as-built photos:
DC In & OSH Push-button Switch

Power Distribution Circuit Board

Wire it Up - LEDs, Next

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