Laser Audio Transmitter Project Question

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SUMMARY

The discussion centers on the laser audio transmitter project, specifically the role of transformers in the circuit design. The user, Capcom, correctly identifies the primary and secondary resistances of the transformer as 8 ohms and 1K ohms, respectively, indicating a step-up transformer. The confusion arises regarding the necessity of a battery pack in series with the transformer, as the user questions the logic of connecting two power sources in series. The conclusion is that while the transformer increases voltage, the battery is essential to provide the necessary current for the laser pointer's operation.

PREREQUISITES
  • Basic understanding of electrical engineering concepts
  • Knowledge of transformer operation and characteristics
  • Familiarity with audio signal modulation techniques
  • Experience with circuit design and analysis
NEXT STEPS
  • Study transformer theory, focusing on step-up and step-down configurations
  • Learn about audio signal modulation and its application in laser transmission
  • Research the requirements for powering laser pointers, including voltage and current specifications
  • Explore circuit design principles, particularly series and parallel connections of power sources
USEFUL FOR

This discussion is beneficial for electrical engineering students, hobbyists working on audio transmission projects, and anyone interested in understanding transformer applications in circuit design.

capcom
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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:

lasertransceiver1.jpg


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
 
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The pointer need a DC input modulated with the AC signal.
 
Most likely this can only be answered by an "old timer". I am making measurements on an uA709 op amp (metal can). I would like to calculate the frequency rolloff curves (I can measure them). I assume the compensation is via the miller effect. To do the calculations I would need to know the gain of the transistors and the effective resistance seen at the compensation terminals, not including the values I put there. Anyone know those values?

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