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powering a propstick from 12v? — Parallax Forums

powering a propstick from 12v?

bozobozo Posts: 70
edited 2008-07-11 17:10 in Propeller 1
The onboard regulator can handle inputs up to ~ 26v, but the propstick usb datasheet specifies using only up to 9v supply ... so I assume there'd be no real drama in running it off 12v? (automotive application) Especially considering that all the propstick will be doing is converting a digital pulse stream from one frequency to another (a speedo recalibrator) ... i.e. the total current load is negligible. Since the application is for a motorcycle, size is critical and I if I can avoid having to step 12v down to 5v it will mean fewer components and smaller size, and smaller is better in this instance.

Anyone got any suggestions before I potentially fry anything?

Cheers,
Mark.

Comments

  • Timothy D. SwieterTimothy D. Swieter Posts: 1,613
    edited 2008-07-11 11:57
    Let me preface with this: I have not used a PropStick.

    Even though the on-board regulators may be able to handle the higher voltages, it doesn't mean in this design that it can handle the voltage. The regulators need to get rid of the excess voltage and this is usually through heat. I am guessing that if you hook it up to 12V DC that it will run for a little while, but may evntually go bananas because the regulator(s) will shut down due to thermal overload. Perhaps if you are running the prop at a low enough speed (less current draw) and really limiting any other current, then maybe it would work.

    I am not sure about motorcycles, but in general automitve voltage supplies can be really dirty with a varying voltage and noise. You might want to consider an external regulator and filter caps for just this reason alone.

    Any one else with directly applicable experience with the PropStick?

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    Timothy D. Swieter, E.I.

    www.brilldea.com·- Prop Blade, LED Painter, RGB LEDs, uOLED-IOC
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  • StefanL38StefanL38 Posts: 2,292
    edited 2008-07-11 15:31
    The problem of overheat can be solved by a 9V-regulator

    Another way could be a stepdown-regulator

    Of course on a motorcycle the size should be small. But what's a supersmall size worth if it fails every few hours?

    So take a regulator that's not too small and mount it on a "cooling aluminium"

    Another question if you really just do frequency translation: what is the factor between the frequencies ? 1:2, 1:4
    For factors like this you could use a dividerchip.

    I'm really a propellerfan but maybe in this case an Atmel Tiny DIP8 would be sufficient too ?

    best regards

    Stefan
  • LeonLeon Posts: 7,620
    edited 2008-07-11 17:10
    The division (or multiplication) has to be fractional. It's needed to correct the speedo reading if the gearing is changed by using different sprockets.

    I agree with the previous poster that a Propeller is overkill for this application, a small PIC or AVR would work just as well and be a lot cheaper. 5V operation would give better noise immunity, as well.

    Leon

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