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Powering LEDs With MSP430 Output


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Just to clear things up here now, I CAN in fact connect any voltage I want for vcc and still switch the transistor on and off with the output of the MSP430, correct?

 

Yes, if you look at the doc cde quoted before. Your LED would go in between R1 and Q1. Except in this case, 12V supply would be 5V and 5V would be ~3V at the MSP430 pin.

Turn the pin High to turn the LED on, and Low to turn it off.

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Thanks cde and GeekDoc!

 

Just to clear things up here now, I CAN in fact connect any voltage I want for vcc and still switch the transistor on and off with the output of the MSP430, correct?

 

Just to be safe, remember, you will have two positive power supplies. One for the launchpad/msp430. And one for the leds. Do not connect positive to positive. Dont want to fry the launchpad.

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be practical, if u are driving individual leds (or a few leds per segment), you need 4 x 9 segment = 36 transistors, it is a lot to do on a breadboard. each transistor has 3 pin, each led 2 pins, each resistor 2 pins will need hundreds of tie-points and the fact that breadboard are connected column-wise (5 points per column), it will be difficult if impossible to lay them out properly.

 

switching from blue to red led is a wise move, u can drive them leds directly if eventually u want to do that. for blues, its not possible because of voltage being too low. get a few red leds and try laying out just one digit. if u are using 7-segment reds, i am sure u don't need transistors, or even eliminate resistors if u do some pwm like switch on / off rapidly.

 

i like breadboarding and always breadboard if possible, and it is more difficult (and challenging) to do breadboard layout than to just grab a soldering iron and use a perfboard, if u are going to breadboard this, i would recommend fritzing, it allows u to work between breadboard layout and schematic at the same time and can generate decent documents. it still alpha but i am using it all along.

 

http://www.fritzing.org

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be practical, if u are driving individual leds (or a few leds per segment), you need 4 x 9 segment = 36 transistors, it is a lot to do on a breadboard. each transistor has 3 pin, each led 2 pins, each resistor 2 pins will need hundreds of tie-points and the fact that breadboard are connected column-wise (5 points per column), it will be difficult if impossible to lay them out properly.

 

Actually, in most cases, you would only need a single transistor per gpio, in his case, 9. Same for the resistor, if the leds are wired in series.

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be practical, if u are driving individual leds (or a few leds per segment), you need 4 x 9 segment = 36 transistors, it is a lot to do on a breadboard. each transistor has 3 pin, each led 2 pins, each resistor 2 pins will need hundreds of tie-points and the fact that breadboard are connected column-wise (5 points per column), it will be difficult if impossible to lay them out properly.

 

Actually, in most cases, you would only need a single transistor per gpio, in his case, 9. Same for the resistor, if the leds are wired in series.

I think simpleavr's math was for all four digits. mnpumar is planning on one MSP430 per digit and one master, so the math is actually conservative.

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