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Replace battery with USB on proto board — Parallax Forums

Replace battery with USB on proto board

SeattlerandySeattlerandy Posts: 7
edited 2012-02-18 10:56 in BASIC Stamp
Why am I paying for 9V batteries ? Looks like I could patch the 5V USB power to the 9V connector + and no more battteries? I would need a jumper across the LM2940 regulator too. The only down side I see is the 5V is now regulated by my PC, might not be as clean and noise free as using the regulator approach. Also would not want to connect any power hungry devices like a servo, because my PC would not provide that much current.

Has anyone tried it ?

Comments

  • SRLMSRLM Posts: 5,045
    edited 2012-02-12 09:10
    Sort of... The 5v pin from the USB connector is really small, so it's difficult to solder a wire to. My solution was to open up a mini-B cable, and solder a wire to the 5v line directly inside the cable. That way I can then plug in that 5v line into the board via that jumper wire.

    In addition, the USB 5v can't go the VIN of the board because there is a 5v LDO linear regulator, which requires something like 6v of input to operate correctly. So, you'll need to somehow get around that. My solution is to remove the 5v regulator entirely, and then the USB 5v line could be used. Note that you shouldn't have both the 5v regulator and the 5v line both trying to drive (or attached to) the 5v rail.

    ps: I too don't know why you're paying for batteries. Just use a wall power supply...
  • SeattlerandySeattlerandy Posts: 7
    edited 2012-02-12 09:16
    Thanks, I just updated my post. An easy place for me to get the 5V USB is on the cathode of the LED's D2 or D3 in my case It would be easier to jumper across the regulator, which places it out of circuit instead of removing it. Then it's easy to remove or cut the jumper when the time comes.
  • SeattlerandySeattlerandy Posts: 7
    edited 2012-02-12 16:46
    I see another potential problem. the BS2 chip on the proto board is wired to get power from V in, which is spec at 5.5VDC min - I think my USB cable/PC will only provide 5VDC. So I would also need to switch the wiring to power the BS2 on VDD instead which is 5V min spec. I think I will measure some USB cable voltages and see how close to 5VDC they are...
  • SRLMSRLM Posts: 5,045
    edited 2012-02-16 21:58
    I'd like to apologize. I assumed that you were using the Propeller Proto Board, which is a different beast entirely. I realize now that it is my mistake.

    Which board specifically do you have? The HomeWork Board or the Board of Education, or some other board?

    If you have the homework board, it looks like the bypass option will work just fine. There is only the one regulator on the board, so it should be fine just to disconnect it and put the USB 5v in it's place.

    If it's a BS2 on a BOE, then it looks like it's still possible, just a bit more difficult. The BS2 has a regulator onboard that could be routed around, the only difficulty being it's small size. The principle is the same, however.
  • SeattlerandySeattlerandy Posts: 7
    edited 2012-02-18 10:56
    I have the Homework board. I measured several USB supplies from various computers and laptops and find an average of 5.1VDC available at the Homework board. This voltage would drop as larger loads are applied.

    As I mentioned in my earlier post this would require rewiring the Basic Stamp chip to remove power from Vin and switch it to VDD.
    I would not recommend this modification for average users... The other suggestion of a wall wort supply is better for most users.

    thanks
    Randy
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