I have read a lot about transistors and I still cannot make my last example work. On the internet I see that transistors are primarily used as switches and as amplifiers.
A) Use transistor as a switch
I want to open and close a circuit. For this example it is a 12 V lamp that I have:
The lamp is on all the time. In order to insert the transistor as a switch I do the following:
Now whenever my digital pin on Arduino is set to HIGH the light turns on.
B) Use transistor as a amplifier
Here is where I am getting stuck.
I want to amplify the signal coming from my aduio cable that is connected to my phone. I connect my audio cable to my phone like this:
I soldered the tip of the audio cable to one cable and the middle part to another cable. I soldered it like that because when I connect those two cables to a speaker I could hear sound. Anyways when I connect those 2 cables to an oscilloscope this is what I get:
As you can see the voltage varies from about -0.2 volts to 0.1 volts. This is what I have tried to amplify the wave:
The voltage varies between negative and positive therefore I do not know what cable to connect to emitter or collector. I have bough a simple 12V speaker. How can I amplify that wave to make the speaker that I bought play louder? In short I just want to amplify the waves that I read on the oscilloscope. WHen I lower the volume on the phone the waves get smaller in amplitude. How can I increase the size of those waves even more?