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I have recently been fascinated with wireless-ness. I thought of a little project so I could do a little research in this area. This project uses a circuit board found in a Christmas card or birthday card that makes it play music when the card is opened. It will also use an RF transmitter and receiver. What I am aiming to do is wirelessly transmit the music from the sound circuit to a speaker via the RF transmitter and receiver.

Parts I plan to use:

RF Link Transmitter (315 MHz) - https://www.sparkfun.com/products/10535

RF Link Receiver (315 MHz) - https://www.sparkfun.com/products/10533

Music Circuit (something similar to this link) - http://www.ebay.com/itm/230761780701

Original circuit: Music circuit -> Speaker

New circuit: Music circuit -> RF transmitter -> RF receiver -> Speaker

What I'm looking to do is cut the wires of the speaker and attach the circuit board to the RF transmitter. And then attach the speaker to the RF receiver. I'm assuming I'm going to need some sort of buffer attached to the receiver. Is there any sort of hardware buffer I would be able to use or would using a buffer through code be easier?

Music circuit -> RF transmitter -> RF receiver -> Buffer -> Speaker

Another thing I'm worried about is the data I will be sending. Would I need an analog to digital converter to change the original signal (that was sent to the speaker itself) to a digital signal for the RF transmitter to transmit correctly? And then would I need to change that signal back to an analog signal?

Music circuit -> ADC -> RF transmitter -> RF receiver -> Buffer -> DAC -> Speaker

Would this be a practical solution?

I know using 2 arduinos would probably be easier, but I want to eliminate the use of micro controllers and code, and focus on the hardware and circuit analysis of the system. Also, I'm using the RF link transmitter and receiver because they are cheap and I want to focus on how the signal is created, sent, and received.

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  • \$\begingroup\$ Those TX/RX pairs can normally handle analog OK and I see that receiver has a linear output so it should work. Be aware though while an interesting project from a practical point of view the results will probably be 'telephone quality'. \$\endgroup\$ – PeterJ Jul 31 '13 at 8:41
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    \$\begingroup\$ If you're interested in the process of sending and recieving the signal, why use a sealed module? You could build a very low power FM or AM transmitter and interact with a normal radio in the same room. \$\endgroup\$ – pjc50 Jul 31 '13 at 8:47
  • \$\begingroup\$ pjc50 is on the right track, a small basic analogue Tx is by far the simplest solutions rather than throwing multiple arduinos at the problem. \$\endgroup\$ – John U Jul 31 '13 at 8:58
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    \$\begingroup\$ You might be able to re-engineer one of those car MP3 adapters. They have an audio input (for MP3 players etc) and transmit a low-power FM signal which is received by the car radio. Whether it could be adapted to work off a lower supply voltage, I don't know. \$\endgroup\$ – MikeJ-UK Jul 31 '13 at 9:05
  • \$\begingroup\$ Hmm interesting. Thank you all for the input. I was thinking of building my own transmitter before. I found this: pyroelectro.com/projects/pyro_rf_transmitter_27mhz but I soon found myself leaning toward just buying one since I understood what was happening on the circuit level. I'll take a look at building an am or fm transmitter and possibly a receiver. I completely forgot about the different modulations. Looks like I have some more research to do! \$\endgroup\$ – slashoofpez Jul 31 '13 at 9:15
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Here's another thing you can do:

You could replace the microphone with the music circuit and then:

  • Use the built in speaker. (Save some money)
  • Replace the old speaker with the new. (If you're feeling geeky today)

Here's a cheap baby monitor on Amazon.

From Amazon.com: Baby monitor

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  • \$\begingroup\$ Would this have good enough quality? \$\endgroup\$ – Anonymous Penguin Jul 31 '13 at 19:17
  • \$\begingroup\$ Have you heard those greeting cards? \$\endgroup\$ – hoosierEE Jul 31 '13 at 19:22
  • \$\begingroup\$ Well yes... but what about interference? He never said his range. I was questioning whether there would be some static/garbling. \$\endgroup\$ – Anonymous Penguin Jul 31 '13 at 19:23
  • \$\begingroup\$ Fair point. I would assume the cheap baby monitor is a poor quality radio in terms of fidelity, interference, etc. But it's cheap and very fast to implement. It has a microphone on the transmitter side, so "wiring it up" consists of just placing it next to the greeting card. \$\endgroup\$ – hoosierEE Jul 31 '13 at 19:40
  • \$\begingroup\$ Yeah I guess. It sure would be fine if it was over short distances, but I would limit how far I would go with it away from the receiver. Even better, find one that sends sound digitally so it can "edit" out all the extra noise. (You could do this also yourself, but you'd have to use a microcontroller, which the OP doesn't want to do.) \$\endgroup\$ – Anonymous Penguin Jul 31 '13 at 19:43

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