Sending Music through a Frequency-Modulated (FM) Infrared (IR) LED

Hello Instructables community! Welcome to my first project upload. This was actually my Freshman Electrical/Optical Engineering Final Project at the University of Alabama in Huntsville. It was actually categorized as a higher level project--for junior or senior students--but my group decided that all the suggested freshman-level project options weren't challenging enough. This is actually a modification of MaxmCarter's High Fidelity Laser Audio Transmitter (http://www.maxmcarter.com/lasrstuf/lasermodulator.html). During the process of the build, we had to change the design around a bit so that we could directly connect it to an ipod. We also found a couple of mistakes and redundancies that we had to modify. Nevertheless, we still use the same Intergrated Circuits (ICs). If you are looking to transmit your voice over an FM laser maxmcarter's design might suit you better. However, if you want to transmit your music through FM by optical methods, look no further!

So why FM?

Well . . . that is a very good question. In highschool I attempted to transmit music through amplitude modulation with a cheap laser pointer and the noise was unbearable. Turns out that ambient light created a sort of feedback that made my project very inefficient. If the lights weren't out, the reciever wouldn't play my signal. Even with the lights out, only one song was audible--"Hey Soul Sister" by Train. So the purpose of this project was to fix that bug. We wanted to be able to send music in the middle of the day as clear as possible. With FM, we could set up a series of oscillations that would fix that. The circuit forms a free-running FM oscillator/modulator operating at twice the operating output frequency. This is the core of the modulator. The output is linear ramping voltage of either positive or negative slope.


And why an IR LED?


We originally planned to use a laser pointer and a photodiode. However, it turned out that we bought the wrong photodiode--we had a blue photodiode receiving red laser light. We realized this at the very last minute and had to change to parts we already had--an IR phototransistor paired with an IR LED. If you want to use a laser pointer and a correct photodiode, you can simply replace these components.


Either way, this was the Intro and I hope you will enjoy building this project. It's a bit challenging but I will try to make it as simple as possible.  

Step 1 Parts list for Modulator/Transmitter

So here it is, the parts list.

For the transmitter:

 Capacitors

 .1uF ………………………….5

  4.7uF (25V)………………2

  270pF……………………….1

  1uF (35v) ………..……….2

  .001uF………………….…..1

  .01uF…………………….….1

  10uF (25v)…………………1

  100uF (16v)………………1

Diodes

  1N5817 (Schottky rectifier)……….2

  IR LED………………………………………….1

  1N914…………………………………………1

 Resistors

  10k…………………………………………….5

  2.7M……………………………………….…1

  270k…………………………………………..2

  100k…………………………………………..4

  2.2k………………………………..………….1

  33k…………………………………………….1

  560 Ohm………………………………..….1

  240 Ohm……………………………….…..1

  2 Ohm………………………………………..1

 ICs

  LF347 (Quad JFET op-amp)……………………1

  CD4069 (Hex CMOS inverter)………………………..1

  CD4013 (Dual CMOS D flip-flop)…………………….1

  TC1411 (HS driver)(Digikey TC1411CPA)………..1

  LM317 (Voltage regulator)…………………….……..1

Potentiometers (trimmers)

  100k (trimpot)……………………….…..1

  10k (trimpot)………………………….…..1

  500 Ohm (trimpot)……………………..1

you also need a Breadboard and many connectors/wires

I suggest you purchase the ICs through Digikey.com, The Pots and diodes through Radioshack, and the rest through Jameco. Doing this, my modulater cost me about $45-60. I bought most parts in exccess. I suggest Part no. 20812 for breadboard. You can also use a regular breadboard if you wish to work under a budget.

Comments

[BitBoink]

Nice instructable!
I've done this with lasers... but IR would be cheaper and invisible.
Will try this.

BTW - what really grabbed my attention at first was that I thought it was a picture of my equipment! I have the same exact power supply and auto ranging fluke meter! haha... was a little weird at first glance :)

[Jamaal_7lna]

haha yeah... we planned on using a laser pointer but figured ouit we bought the wrong photodiode at the last minute:/ I was looking foward to that long rage too....