Laser Audio Transmitter Project Question

[capcom]

Hi everyone,

I'm attempting the laser audio transmitter project. And example of it is found here: http://www.freeinfosociety.com/site.php?postnum=2310

I'm quite new to electrical engineering type work, and am a little confused by why the circuit works the way it does. The diagram is this:

Now, I read up on transformers, and as I understand it, the primary end is 8 ohms because the number of turns create that resistance. Likewise, the secondary is 1K ohms, so it is a step up transformer. That would be because the voltage coming through the audio jack from my mp3 player would be too low to power a laser pointer.

If that's correct, then I don't understand why at the other end, I need the battery pack to power the laser. I'm guessing that while the transformer provides the correct voltage for the laser, the current is not high enough. Considering this is also right, what I finally can't understand is why the battery is connected in series with the transformer. I thought if you connect two power sources in series, the voltage doubles, and if you connect them in parallel, the current is summed. What is the flaw in my logic here?

I really appreciate you taking the time to read, and hopefully answer my question.

Best wishes,

Capcom

 

[anorlunda]

The pointer need a DC input modulated with the AC signal.