Designing a transfer system of audio and control on one wire - Page 1
Forum section: electronics / projects

author: maor
author_rank: Contributor
timestamp: October 26, 2012, 12:12:32 pm
content: So while I'm waiting for my attinys to get here, I thought of an idea to transfer a switching signal on the guitar line while still transferring the audio signal.I'd figured it won't be that hard, let me define it:Transmitter:The guitar transmits a 440p-p(typical) voltage on a passive load, this signal is band limited using the "tone" circuit of the guitar.On the same line, an attiny will switch a reference signal (about 1Mhz if I can create that on the attiny using a timer) which will go trough an RC filter in order to cut the edge off the harmonics of the signal so it won't have as much effect on the large signal.Receiver:On the receiver side, the signal will be buffered to control the impedance.the signal splits in to an lp and an hp filter, to get a 1Mhz sine wave of the switching signal and the guitar audio.I tried testing this on multisim to prove the concept, and it worked!I added the circuit I tested.The big question is, is this design correct? will it work?, is there something I should add?

author: poptones
author_rank: Frequent Contributor
timestamp: October 26, 2012, 05:54:06 pm
content: Give it a shot, it may sound alright. My suspicion is, with all that RF into that first op amp, it's going to have a good bit of IMD that may or may not be audible. If it doesn't prove out you could always try subaudible tones - very low frequency tones that act as control signals.

author: SeanB
author_rank: Super Contributor
timestamp: October 26, 2012, 07:22:13 pm
content: You will need to generate a very pure sine wave to use as a signal. Try using a LC oscillator at around 455kHz, MW if transformers are cheap, small and low cost, and you can use the 455kHz IF resonators as a filter on the signal both ends, and this will be easy to both inject and extract at both ends. This will not interfere with the audio from the guitar. no micro, just cheap and stable ceramic filters and a simple diode detector or even an AM receiver chipset to demodulate the signal. a 455kHz IF coil on the input to the guitar am will attenuate the signal applied to the audio amplifier while having almost no effect on the low level audio.

author: maor
author_rank: Contributor
timestamp: October 27, 2012, 07:45:01 am
content: Quote from: SeanB on October 26, 2012, 07:22:13 pmSo you want me to make a superhetrodine receiver? Sounds like a bit of an overkill for this project.I'll test it out once I get the attinys here, if I'll get some issues it's back to the drawing board anywayQuote from: poptones on October 26, 2012, 05:54:06 pmThe problem with subaudiable tones is that they will generate an impulse on the output which will create an audible click.and the bigger problem is to make a filter to use that will require some really, really large components, making it entirely pointless to create.

author: SeanB
author_rank: Super Contributor
timestamp: October 27, 2012, 09:57:38 am
content: Not a superhet. Just the IF stages as the frequency is well above audible, and the parts are both very cheap and common. All you need is a diode detector ( or a transistor with appropriate bias and a collector cap to do the averaging) to get an output signal, and a high purity sine wave will both be easier to mix in and filter out and will give no plopping on switching on and off.Think of GSM interference, where you have a 800 odd Hz digital switching of a 900MHz carrier generating interference.

author: NiHaoMike
author_rank: Super Contributor
timestamp: October 27, 2012, 08:55:34 pm
content: What about just shift the DC bias level, lowpass filtering it so that transients will not have much content above 20Hz?

author: poptones
author_rank: Frequent Contributor
timestamp: October 27, 2012, 09:39:43 pm
content: Replace the mono guitar cord with a stereo cord. Use one wire for the guitar sound, one wire for control. Done.