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Topic: [SOLVED] How to choose a transistor ? (Read 3248 times) previous topic - next topic

MAS3

Did you order a set of resistors to go with it ?
Saves some shipping costs.
Have a look at "blink without delay".
Did you connect the grounds ?
Je kunt hier ook in het Nederlands terecht: http://arduino.cc/forum/index.php/board,77.0.html

007good

#16
Jul 28, 2015, 03:28 pm Last Edit: Jul 28, 2015, 03:36 pm by 007good
Hello guy,

I have recieved my PNP transistor.
I plugged it at the exact same as yesterday. And now have the exact opposit problem. The segment is ON whatever I say to Arduino, LOW or HIGH it's always ON.
I tried to mannually plug the base of the transistor to the GND then the segment switch OFF. It look like HIGH or LOW, the Arduino always deliver something.

What look very strange... Is when I unplug the USB cable of the Arduino, it is still a bit powered, the "ON" Led of the arduino light a bit (And the segment remain ON).. That probably mean power from the 9V battery goes a bit to the arduino trough the base of the transistor into Pin 2 ???
That may explain it doesn't work ?

Edit : Sorry.. Base to the GND, Segment is ON. Base disconnected, segment is OFF

MAS3

What transistor did you use, and how did you wire it ?
Did you have a look at the datasheet for that transistor ?
Did you compare what you built, with CrossRoads' drawing ?
Have a look at "blink without delay".
Did you connect the grounds ?
Je kunt hier ook in het Nederlands terecht: http://arduino.cc/forum/index.php/board,77.0.html

007good

BC557 as you told me.
Yes I took a lot to be sure which pin was emmiter/collector/base.

Power to the collector
Pin 2 to base trough resistor
Emmiter to + of the segment trough resistor

Cathode of the segment to ground.


MAS3

The base of a NPN transistor opens when you "push" it up.
The base of a PNP transistor opens when you "pull" it down.


Remember the two diodes i told of ?
Actually it's more like one and a half diode.
The N stands for Negative layer , the P for Positive layer.

The diode part means that current is stopped when it reaches the center layer.
But as soon as you start manipulating that center layer by applying a current there, the diode function is altered, and the outer layers will bridged by the now conducting center layer.
That's how a transistor functions in a nutshell, there's much more about it.
Have a look at "blink without delay".
Did you connect the grounds ?
Je kunt hier ook in het Nederlands terecht: http://arduino.cc/forum/index.php/board,77.0.html

007good

So, the good question is how to pull it down thanks to the arduino ?????

MAS3

Pulling it down will make it go LOW ?
Have a look at "blink without delay".
Did you connect the grounds ?
Je kunt hier ook in het Nederlands terecht: http://arduino.cc/forum/index.php/board,77.0.html

007good

I managed to do the thing by connecting one PNP from power to the anode with the base connected to a NPN which link the PNP to the ground controlled by the arduino.
Is there any better solution ??? Or I have to use two transistor ???

MAS3

So you have created an inverter so the signal you are sending out gets inverted to control the PNP.
How about writing an inverted signal to the PNP in order to enable it ?
What happens if you make pin 2 LOW ?
Have a look at "blink without delay".
Did you connect the grounds ?
Je kunt hier ook in het Nederlands terecht: http://arduino.cc/forum/index.php/board,77.0.html

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