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MSP430G2 Launchpad Vcc pin

Laura Rivera
Prodigy 30 points

Hi, I am using the MSP430G2 Launchpad to control a water pump that requires 3.5v to 9v and 3w to work. The problem is that when I use a pin (say P1.4) the pump does not turn on; but when I use the Vcc pin it does work, I do not know if I can control the Vcc pin with software (I am programming with assembly). If this is possible, can someone tell me how to do it with assembly instructions? Thanks

  • 0
    Guru 74080 points

    Hi Laura,

    you cannot connect such a high load to the MSP - you should not sink or source more than a few milliamps on a pin. Even connecting a 3W load to the Vcc pin of the LaunchPad isn't a good idea. Do some math: The USB provides 5V, so 3W / 5V = 0.6A - but you can only draw a maximum of 500mA from a normal USB port (and this has to be declared to the system first). Furthermore the TPS77301 voltage regulator on the LaunchPad can handle a maximum of 250mA, so even if your load does not need the 0.6A at a supply voltage of 3.6V (this is the voltage produced by the TPS77301), the voltage regulator might be overloaded.

    And no, you cannot switch the Vcc pin on and off. In that case the micro would switch it's own supply on and off, too. Use a transistor to control the pump. And think about an external power source for it.

    Dennis

  • 0 in reply to Dennis Eichmann
    Prodigy 30 points
    Thanks for your help Dennis. I have already tried using a transistor and an external power source but the motor won't turn on. I have used a BJT as a common collector to amplify the current and also the Darlington configuration but I dont seem to achieve the desired voltage and current (if I have the necessary current, the voltage is to high for the motor, or if I have the desired voltage the current is too low). I have also tried using an opamp but no success.
  • 0 in reply to Laura Rivera
    Guru 74080 points
    A transistor did not work? Could you show how you tried to connect the motor and the transistor? The Darlington configuration is well suited for driving a high current load with a very low current.
  • 0 in reply to Dennis Eichmann
    Prodigy 30 points

    I have tried these configurations with npn transistors. I have also tried using 6v battery in series with the voltage of the P1.4; also I have tried connecting the external power source to the collector and the P1.4 to the base, I have tried using various resistors to lower the voltage but the current drops dramatically when I do this.

  • 0 in reply to Laura Rivera
    Guru 46710 points

    Don't you think that wheel is already invented? :) Anyway it is advised to check first before even you try

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