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USB source of power for BOE / Homework board? — Parallax Forums

USB source of power for BOE / Homework board?

John KauffmanJohn Kauffman Posts: 653
in BASIC Stamp
For powering devices there is now a plethora of options at USB voltage (5v). My favorite are here:
voltaicsystems.com/6-watt-kit. They work fine directly with the Prop Activity Board.

But many of my students have a BOE, BOEBot or Homework. These BS2 boards are set up for 6-9v. Has anyone tried running BS2 boards at USB voltage? I'll give a try to stripping out a USB cable and soldering its power leads to a jack (or 9v clip). Any thoughts on a adding a buck-up from 5v to 7v?

There are lots of discussions here about rigging up solar, supercaps, battery charging schemes, etc. But they ecosystem is well developed for USB power. It would be great to have a plug-n-play solution.

Comments

  • ercoerco Posts: 20,257
    Sure, any Stamp can be powered directly by a clean 5V supply which can maintain voltage under load. Servos are power mongers and generate noise so they might need their own seperate power supply.


    It is funny that USB has evolved from a communication connection to a power connection. I see a lot of defective or broken electronic items which have a bad USB mini or micro connector. Not sure if those connectors were intended to be connected & disconnected daily or more often.
  • John KauffmanJohn Kauffman Posts: 653
    Thanks for sharing experience. I was thinking that 5v in then through the voltage regulator would mean ~4.5.

    I agree on current requirement for servos and relays.

    Next step is soldering the physical connections. I have a bag of the male jacks and some 9v clips so should not be hard.
  • PublisonPublison Posts: 12,366
    USB 5 volts to the 9 volt clips will not work, the regulator needs at least 6.5 volts to work. You could connect 5 volt USB voltage the Pin 21 to bypass the regulator, but it is hard to get to unless you inject the 5 Volt through the VDD on the header. I would call Tech Support before doin that.
  • ercoerco Posts: 20,257
    It might be more complicated than I first thought. Per http://forums.parallax.com/discussion/83749/bs2-5v-on-board-regulator-w-boe ,

    and it looks like, from the schematic, that in fact the on-module regulator DOES provide power for the BS2 on the BOE, while the BOE-board regulator powers the rest of the circuitry.

  • John KauffmanJohn Kauffman Posts: 653
    Ok, back to my original thoughts.
    Interesting comment on the min value 6.5v - input jack says 6-9.

    Any comments on using a DC-DC step-up module to go from USB 5v to something like 7-9? I've never used them before.
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