project:laser_modulation [Labka Hackerspace Ostrava]

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====== Transmitting sound frequencies by using the modulated laser beam ======
**Project owner:** Ivan_Ahepjuk

**Main goal**: get to the at least step 7

**Introduction:**
Hopefully there will not be big fails. Still, It would be challenge to tune and tweak the concept and build robust design with using as little parts as possible. I would like to use green laser, because i got it at home and I think that its strong enough to transfer from my rooftop to the Ema hill.

  * **step 0:** Think, ask and read how to use laser beam to transfer sound frequencies. Think how to receive this kind of information. Understand the principles.
  * **step 1:** Do initial design of the transmitter circuit. Use operational amplifiers, no microprocessors, no programming. Use cheap components, think about robustness and simplicity. Find own solution, do not follow allready made and proven designs.
  * **Step 2:** Prove the design by computer simulation, choose right components, tweak components values for the best fit.
  * **Step 3:** Build the prototype, prove the concept, celebrate as hell.
  * **Step 4:** Do initial design of the receiver part. Again - no microprocessors, "only" operational amplifiers.
  * **Step 5:** Prove design by computer simulation, choose right components, tweak components values for the best fit.
  * **Step 6:** Build the prototype, see it working with transmitter, do succesfull transmission of the song [[https://www.youtube.com/watch?v=iqgO1lZkqoo|Ivan Hlas - Karlin]] from the rooftop in the Ostrava city centre to the top of the Ema hill. Celebrate as double hell!
  * **Step 7:** Make pcb, write conclusion, process the documentation for followers.

====Main solution:====

**Step 0:** Initial research: My green Laser diode (from green laser poiter, ebay, 4dollars) is emmitting light if there is around 2.4V on it. Difference between laser "off" and laser "on" is couple of 10mV (while sinking 0 - 250mA). Therefore, one way is to amplify the amplitude of sound signal to lets say 20mV, then add a reference  around 2.4V, make the signal more robust by voltage buffer  and feed this to the laser. 
But **1]** This solution doesnt count with intensity loses on the way from laser emittor to the receiver and 
**2]** It would be pain in the ass to calibrate this and it would change with "each blow of the wind". There are better way and they are called modulation.

  * **Pulse-Width Modulation**: The main idea is to make laser flashing at certain frequency and while transmitting, be changing the width of pulses by the transmitted frequency
  * https://en.wikipedia.org/wiki/Pulse-width_modulation. 


**Step 1:** Initial design: This is basic idea how to build the transmitter. 
  * All amplifiers are LM358N
Cannot upload pictures:/


**Step 2:** simulation by LTspice (maybe little tutorial how to use ltspice would be more than good)
Cannot upload pictures:/
**Step 3:** Photo of actual prototype
Cannot upload pictures:/
**Step 4:** stay tuned