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On my current project I am trying to get the MSP430G2211 to turn on a 12 volt pump for a certain duration. I have all the other logic and coding worked out and done, but I am at an intersection as to how to convert the 3v out signal to control the pump.

(see diagram attached)..

Do I use some transistor to hit a Power MOSFET (I have an IRF510) and then use that to activate the relay (not sure on how to configure that)..

Or do I use the IRF510 or something similar instead of a relay? (never used a MOSFET for anything before)..

Or perhaps a better idea yet?


water pump.doc

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Use a multimeter to check the current draw of the relay. If it is under 200mA, which it probably is, you could just use a simple npn3904 transistor. You can buy one for over a dollar at radio shack, or you can stalk up dirt cheap from here: http://www.taydaelectronics.com/servlet ... 904/Detail

When I order they usually take a little over a week to the U.S., so keep that in mind if you are in a hurry.


You will need to look at the datasheet for it to know which pins are which (be careful, if set it up wrong you may accidentally drive the relay from the I/O which will destroy it) but if you would like I can see about finding you a schematic tomorrow if you need one.

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my prefered way driving relais is with an optocupler!!


it has a lot of advantages like you can use any relais like 3v 5v 12v cause you are independent of your uC's voltage


you don't have to calculate if your transistor will fit just take a relais an optocupler and a diode and the relais...


driving an optocupler is simple, cause it's like driving a led


you can also have also seperation of the switching and the controlling circut if you want to...


i think it's a much simpler and more flexible way to drive a relais


and i think the pirce doesn't matter cause an optocupler is like 20c


i have a layout with 4relais 4optocupler and 4 leds for optical visualisation... if you want i can give it to you, but i have never tested it, but ill soon do so!

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Thanks zeke for the nice pointer to all the relay circuits.. I actually ended up copying one of them for my circuit (now posted in projects).


As for mystboy and optocupler, thanks for the idea but it looks like I have found a solution with the parts I have on hand.

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