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test circuit

Adam BrooksAdam Brooks Posts: 5
edited 2010-06-22 15:10 in General Discussion
Just curious, I am working on a project with nitinol wire, I plan to use two pins to drive the wire and another pin to sense activation. The sensing circuit is simple, source Vdd a 10k resistor before the pin and finally a switch leading to vss. The driving ckt for the wire however first has the DAC ckt proposed by the handbook a 1k resistor/1 microfarad capacitor with the nitinol wire connected in parallel with the cap. Before the nitinol however is a high freq switching MOSFET transistor, the DAC supplies the collector, the nitinol hooked to the emitter and a pin with a 10k limiting resistor controlling the base current. Everything also has protection diodes.

Now the question, the nitinol wire needs 400mA to activate so I am testing voltages from 2.08V to 3V using the DAC. Is this too much current to draw from the stamp?

Thanks,
Adam

Comments

  • jmspaggijmspaggi Posts: 629
    edited 2010-06-22 14:20
    Hi Adam,

    On Javelin's documentation, they say "Note that the onboard voltage regulator can accept between 6 and 24 VDC and output up to 150 mA of current. Since the Javelin consumes approximately 60 mA, you have 90 mA available for other uses."

    So I don't think you will be able to drive 400mA from it.

    There is also "Sink/Source Current per I/O 30 mA". So I will recommend you to add something between you nitinol and the Javelin.

    JM

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  • Adam BrooksAdam Brooks Posts: 5
    edited 2010-06-22 14:47
    Yeah i just saw that, I am thinking about buying a wall transformer from radioshack that supplies 3V and can handle the 400mA load of the wire then just tie the ground from the 3V into the ground on the Javelin so that it will be common and then wire with just the transistor switching ckt. Is that ok to do wiring two different grounds together?
  • jmspaggijmspaggi Posts: 629
    edited 2010-06-22 14:56
    Hi Adam,

    That's the right way to do it.

    I have my javelin using a +5V power suply, linked with a DC-16 board using a +24V power suply. Both of them are ground connected.

    JM

    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    Linux? There is worst, but it's more expensive.
  • Adam BrooksAdam Brooks Posts: 5
    edited 2010-06-22 15:10
    Awesome thanks a lot!

    -Adam
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