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Prop Educ Kit: drawing too much current? — Parallax Forums

Prop Educ Kit: drawing too much current?

TimZTimZ Posts: 4
edited 2010-06-21 18:50 in Propeller 1
Hi,

I've got the 40 pin DIP Version of the Propeller Eduction Kit.

I'm able to run the PING sensor, an LCD (with backlighting) and a GPS (all from Parallax) individually. They are all 5 volts and powered from the 5 volt supply on the kit board.

But I can't run them at the same time. If I have the ping and the LCD running and plug in the GPS things go bad.

Am I drawing too much current? What alternatives do I have?

Thanks!

Tim Zajic

Comments

  • W9GFOW9GFO Posts: 4,010
    edited 2010-06-20 00:39
    A 9 volt battery is not going to last long like that. Nearly half of the energy is converted to heat in the linear regulators to bring the voltage down.

    If you have a 6-12 volt wall wart you could use that as a power supply or you could use a battery pack, such as 4 AA cells. I use either a five cell NiMH battery pack or a wall wart.

    Rich H

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    The Simple Servo Tester, a kit from Gadget Gangster.
  • johnnycarlosjohnnycarlos Posts: 44
    edited 2010-06-20 01:54
    I can also attest that a 9V battery doesn't last long, mine died just today. Interestingly enough, my device would fail at a certain point in the code: blink an LED. It would blink twice and then the program would stop. Thought something was wrong with the code until I couldn't connect to the chip at all, then I realized it was the battery. And I never even tried to drive any peripherals.

    It motivated me finally get a real power supply running. Couldn't be happier.

    John
  • TimZTimZ Posts: 4
    edited 2010-06-20 11:25
    I do have a wall wart: can I plug it in just as the 9-volt plugs into the Prop Ed board, or do I need to build a new regulator to make it so I can drop to 5V from the 12V wall wart?

    Also, is there a way to determine how much load a 9-volt can take before performance is impacted?

    Thanks all!

    Tim
  • eod_punkeod_punk Posts: 146
    edited 2010-06-20 13:35
    The 5 volt regulator that comes with the kit can handle the 12 volts. Just make sure you hook up the positive and negative coming out of the plug correctly. Someone on this board a few months ago hooked them up backwards on their Professional Development Board and fried it.

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    There is no problem that can't be solved with a suitable amount of explosives!

    EOD Memorial
  • johnnycarlosjohnnycarlos Posts: 44
    edited 2010-06-20 16:13
    The data sheet of the LM2940CT-5.0 says it can handle up to 26V

    http://www.parallax.com/StoreSearchResults/tabid/768/txtSearch/lm2940/List/0/SortField/4/ProductID/242/Default.aspx

    The kit came with a .47 uF capacitor that needs to be put across the terminals, as described on Page 30 of the PEK Lab Book.

    Good luck,

    John
  • ForrestForrest Posts: 1,341
    edited 2010-06-20 16:30
    If you use a wallwart, you'll also need to install a capacitor across the Voltage Input pin and ground, as described the regulator's data sheet. You'll also probably want to install a heat sink on the regulator if you need more than 100 mA (for the GPS).
  • Andy Lindsay (Parallax)Andy Lindsay (Parallax) Posts: 1,919
    edited 2010-06-21 17:30
    Hi Tim,

    I use a 6 V, 1000 mA wall supply with a little adapter that has a 9 V battery output terminal. A 6 or 7.5 V regulator output with a high current rating (1000 mA or more) is important. Rechargeable hobby battery packs in the 6 to 8 V range are also good.

    Higher supply voltages reduce the regulator's current output capability because the regulator is limited by how hot it can get, and it generates more heat with higher input voltages. A heat sink will definitely help. Another alternative is to build a second 5 V regulator to supply certain power-hungry 5 V parts. The regulators could share the same supply, or each one could draw from a separate supply. Just make sure the grounds·are common (negative terminals tied together) for all supplies and regulators.

    Andy

    P.S. Radio Shack doesn't carry my little 9 V battery adapter any more. If anybody has a pointer to a good adapter, please do share. Thanks.

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    Andy Lindsay

    Education Department
    Parallax, Inc.
  • johnnycarlosjohnnycarlos Posts: 44
    edited 2010-06-21 18:50
    I am using a multi-voltage regulated supply. It can put out 3, 4.5, 6, 7.5, 9, or 12 volts at the turn of a knob. It's $22, but having all those voltages available makes it priceless. I can connect to just about any battery powered device using aligator clips for when I don't have(or don't want to use) batteries.

    Andy's adapter gave me an idea. a 9V battery clip spliced to a banana plug cable used by the supply would make it even more convenient. And the banana plug cables also stack, so you could easily connect additional devices, up to 2 amps. What a deal.

    John
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