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Prop Demo Board question — Parallax Forums

Prop Demo Board question

NWCCTVNWCCTV Posts: 3,629
edited 2012-10-05 10:56 in Propeller 1
OK, So I just received my shiny new Propeller Demo Board. I just have one question before I get started. I plugged in the USB cable and my system found it without any problems and everything installed. I have not yet plugged a power supply in and I just want to make sure that it has to be plugged in for the Spin program to find it, or should it find it without having the external power??? I know this may seem like an odd question, but I just want to make sure I have it right before frying anything. I have one of the 7.2V wall warts from Parallax I am planning to use with it.

Comments

  • PublisonPublison Posts: 12,366
    edited 2012-10-04 18:20
    NWCCTV wrote: »
    OK, So I just received my shiny new Propeller Demo Board. I just have one question before I get started. I plugged in the USB cable and my system found it without any problems and everything installed. I have not yet plugged a power supply in and I just want to make sure that it has to be plugged in for the Spin program to find it, or should it find it without having the external power??? I know this may seem like an odd question, but I just want to make sure I have it right before frying anything. I have one of the 7.2V wall warts from Parallax I am planning to use with it.

    The Demo Board will not run off of USB Power, so a 7.2 V wall wart will do nicely.
  • Phil Pilgrim (PhiPi)Phil Pilgrim (PhiPi) Posts: 23,514
    edited 2012-10-04 18:20
    Unlike with the QuickStart and PropBOE, you need external power with the Demo Board.

    -Phil
  • NWCCTVNWCCTV Posts: 3,629
    edited 2012-10-04 18:23
    That answers my question. Thanks guys.
  • Peter JakackiPeter Jakacki Posts: 10,193
    edited 2012-10-04 18:37
    I always power my old demo board from the USB port, all you have to do is link across from the USB +5V to the output of the +5V regulator. It's not rocket science.
  • Phil Pilgrim (PhiPi)Phil Pilgrim (PhiPi) Posts: 23,514
    edited 2012-10-04 19:38
    I would never do that, except with a powered hub to isolate my PC from current surges. The USB spec calls for a soft start circuit to limit peak currents. The Demo Board, unlike the QS and PBOE, does not provide such a facility.

    -Phil
  • Peter JakackiPeter Jakacki Posts: 10,193
    edited 2012-10-05 00:55
    Um-mm, so does that mean I've blown up all my laptops? Hardly, the Prop starts soft because it's in reset before a single cog switches on using the internal 12MHz oscillator before possibly ramping up power running the user code. Max current by then? About a third of the 500ma that USB ports are rated for. Of course I'm not trying to stick motors and relays onto 5V, just the demo board and basic stuff. Anyway I've been doing it for years on a wide variety of equipment. There are also a wide variety of those USB powered gadgets around which do not observe this soft-start (not that I'd use them).
  • Phil Pilgrim (PhiPi)Phil Pilgrim (PhiPi) Posts: 23,514
    edited 2012-10-05 10:56
    The Prop might "start soft", but there's still a surge current to charge the filter caps. And, if you add more capacitance in the breadboard area, it gets worse.

    -Phil
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