2nd year EET project

mattm_nscc

Guitar distortion & and wireless amp
Hello fellow, students & techs. I am, along with my project partner, are in our 2nd year EET program at NSCC.
We have decided to do the following microcontroller project. We want wirelessly transmitt the guitar signal to a amp/distortion box. Our first idea was to combine it all into the guitar but after some consideration we decide to go with the wirless idea instead.
For my part of the project i have to design something to transmit the signal wirless to the amp unit. My question(s) to you is ,

1) do you think i can transmit analog signal wirelessly of should i use a ADC and then transmitt it on a 433Mhz transmitter ?, or something similiar ( sorry im a noob).

2) We want to be able to switch to normal guitar or distortion on the guitar ( one type at the moment ) , I assume we will need a multiplexer to do this ?

3) If we want to have an LCD which shows the type of distortion , and prehaps a guitar turner, will we need a transciver in that case to send info back to the guitar ?

4) And we are using the parallax BOE as our microcontroller final project , if we want to drive 2 trancivers , one from the guitar and one from the amp, will we need two BOE's to make it work ?

We're all in this together ( figuratively) so any comment or suggestion will be greatly appricated, Thanks !

Mike Green

You have a lot of learning to do. The toughest part is to transmit the guitar signal with good fidelity and low noise. You might start with a commercially made wireless microphone and send the control information using a low frequency signal combined with the guitar signal that can be filtered out at the other end. Back before PowerPoint, for an automated slide show, you might have a voice / music recording with pulses of low frequency sound that would be used to trigger the slide advance mechanism. The voice / music would typically occupy 40Hz to 20KHz or something like that and the control pulse(s) would be at 20Hz or 25Hz. You'd have a tone generator for 20Hz that would get mixed with the music and, at the receive end, you'd have a sharp 20Hz filter and detector, then a high-pass filter for the music that would start to cut off at 40Hz. If you want something more complex than one on/off signal, you could two frequencies, maybe 20Hz and 30Hz with one representing 0 and the other 1 and encode a number with several pulses in a row.

Another option would be to use separate RF channels with a 433MHz audio channel (wireless mic) and a pair of xBee transceivers at 2.4GHz to provide a bidirectional control channel for the distortion box and feedback for an on-guitar display.

mattm_nscc

Thanks for the advice.. do to our budget among other factors we have decide to use the 433MHZ transciver.... any general tips or advice on them ?

Mike Green

Do you mean Parallax's 433MHz transceiver? If so, I don't know how you're going to accomplish your goals. This transceiver can handle about 9600 Baud, roughly one byte every millisecond. You're not going to be able to transmit much audio at that rate unless it's highly compressed. It's possible to send data at a higher rate at that frequency, but not with the modulation scheme used in Parallax's transceiver.

Peter KG6LSE

what you are trying to do is not super hard . but the parts needed are not at your local radio shack in bare form ..

BUT I have seen the 2.4GHz video pares on sale .. use the audio for the audio and some how run data over the Video Sig . and Considering NTSC needs to pass Sync pulses you may,Just may,, beable to run the data right on to the jack and have it come out the other side unharmed . will need a amp on the Rx as NTSC does not = 5V TTL ..........

with 5meg plus bandwith for NTSC you have the potentail for a high data rate ..


MUXing data is Old as time .. In fact its done a TON on Cell phones ..........
FDM( Diff Freqs). EG a Set of tones that are not in the same band of data as the voice
TDM( Do each thing one at a time) . EG every Sec for the first lets say 50mS of each second sling a chirp of data in lew of the voice .

CDMA not really doable here ......


Peter

mattm_nscc

Thanks for the info
we have deicide just to get the signal to transmitt wirelessly. with the paralla 433Mhs transcivers.
here how ou project breaks down.
1 guitar signal to pre amp circuit
2- if possible an sample hold circuit
3- ADC 0831 circuit
4 BS2 to 433mhz tx
5 433mhx rx to bS2
6 DAC cicuit
7 amp and speaker
so this is what i have to work with any suggestions ?

Mike Green

As I mentioned in my post #4, you're going to have a hard time getting this to work. Best Baud for a BS2 is 9600. It'll probably take on the order of a millisecond to read the ADC0831 and another millisecond to send the data over the transceiver link. That's 500 samples per second, so you can transmit at most a 250Hz signal. At best, that's an octave below middle C and you won't be able to hear any overtones.

You'll be much much better off with an analog transmitter / receiver. If you have to use digital, you should look for a transmitter / receiver designed for a higher Baud and use something like a BS2px which is faster than the BS2 and can handle Bauds of at least 19200. That's still pretty limited though. You may have to go with something like the Propeller and xBee to get the data rates you'd need.