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Author Topic: [Solved] Inverting TX serial signal - overheating transistor  (Read 1224 times)
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Hello,

trying to communicate using F Bus with a Nokia phone (an no tuto I have found is working as is ...), I got to this point :
the only time I received something back from my Nokia is when I inverted TX signal using a transistor.
Here is the wiring (red part inverts my TX signal):


As I said, this is working fine, but after seconds, transistor is getting hot, as my ATMEGA chip.

I guess I need resistor somewhere, but transistor is still confusing to me.
And when I try to add resistor to "protect" the transistor (my understanding, sorry), the only thing I do is reducing the base voltage, and Nokia does not answer my requests.

Any suggestions ?

Thank you for your help !

PS: by the way, reading the forum, I noticed that serial signal can be inverted using a library and another pin up to 115200 Baud (http://arduino.cc/forum/index.php/topic,146140.0.html). So I'll try this in parallel, but I write down the link for future readers, and I am still interesting in a hardware solution, to understand a little more those confusing transistors ...
« Last Edit: July 03, 2013, 05:09:25 pm by Loic_B » Logged

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Something might already be damaged.

You need two resistors.

http://www.pighixxx.com/abc-arduino-basic-connections/
Card 6, bottom-right. The transistor with 2 resistors is an inverter you can use.

Using pin 0 (RX) and 1 (TX) could conflict with the Serial library and sketch uploading.

The SoftwareSerial library creates another serial port on digital pins.
I read once that it was able to invert the RX and TX, but I'm not sure and I don't know how.
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you're saturating the poor transistor....

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Thank you Erdin.

First for the links, second for the advice.
My transistor is not overheating, signal can be inverted apparently.

But my project does not seem to work as explained in tutos ...

By the way, nothing get broken, but my finger when touching hot transistors !

I'll ask new questions in a separate topic. Communicate using F Bus is a nightmare ...
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Quote
My transistor is not overheating, signal can be inverted apparently.

By the way, nothing get broken, but my finger when touching hot transistors !
How come if it is not overheating your fingers get hot.
You need a resistor in the base of that transistor.
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Don't use the transistor like that !
It doesn't matter if it works (a little), it is wrong.
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wrong? it's an abomination to all transistors out there!


add a resistor, that transistor should NOT get warm, hot... anything but cold, it means you're damaging the arduino > 40ma i'd love to measure the current draw!
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Nothing get damaged.
Problem already solved.
Schematics linked by Erdin were useful to understand how to use a transistor.
Thanks.

Is there a way to show topic is solved (and hence can be closed ?)
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You can change your first post, and alter the subject. Write [solved] in front of it.
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