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HomeWork Board Current Draw - Wake/Sleep — Parallax Forums

HomeWork Board Current Draw - Wake/Sleep

HumanoidoHumanoido Posts: 5,770
edited 2008-10-13 17:20 in BASIC Stamp
The manual page 5 says the board draws 10ma awake and 40ua sleep with the LED off.

www.parallax.com/Portals/0/Downloads/docs/prod/boards/HomeWorkBoard-v1.3.pdf

My Homework boards (2 tested) draw 16ma awake and 9ma sleep.

I use a digital bench dc power supply with voltage and current readouts, and run the code listed in the manual.

Why is there a great difference between my readings and Parallax' readings?

Comments

  • allanlane5allanlane5 Posts: 3,815
    edited 2008-10-13 16:04
    Because you didn't use the "Sleep" keyword?

    Because you have an LED still on?

    Because you've got a USB adapter connected? Or the serial port still connected?
  • ercoerco Posts: 20,259
    edited 2008-10-13 16:51
    If you were supplying 9 volts through the battery connection points (as opposed to using 5V applied to Vdd) there would be some losses through the voltage regulator. Obviously, any external circuitry will draw more current as well.

    BTW, does the on-board LED turn off in sleep mode?

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  • Tracy AllenTracy Allen Posts: 6,664
    edited 2008-10-13 17:10
    Maybe that current applies only to the BASIC Stamp itself, not to the entire homework board. The Stamp itself will draw about 40 uA sleep current to keep its watchdog timer alive. It is the voltage regulator that draws most of the current.

    The LM2940 voltage regulator has a rather high quiescent current, up to 10 milliamps even at zero load, and maybe that accounts for the excess 9 miilliamps. It is a low dropout regulator, but certainly not micropower. The discussion of the battery life it kind of off target, if it does not include the regulator in the calculations.

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    Tracy Allen
    www.emesystems.com
  • Tracy AllenTracy Allen Posts: 6,664
    edited 2008-10-13 17:20
    erco,

    The homework board LED is connected to the 24LC16 clock line, so that when the clock is high or when the Stamp is sleeping, the LED is off. The LED flashes very rapidly when the clock is active, that is, any time the Stamp is executing code. A clever scheme.

    I notice that earler versions of the homework board (A & B) used the LM2936 regulator, which is indeed a low quiescent current regulator that draws only a few microamps. That is the same regulator found on the BS2-IC modules. However, it can supply only 50 mA max. In versions C & D of the homework board, they switched to an LM2940, which can supply up to 1 amp for more ambitious projects. A good idea, but not good for the quiescent current or for battery life. My guess is that the homework board manual was written in consideration of versions A & B and was not revised for C & D. Stephanie?

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    Tracy Allen
    www.emesystems.com
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