RF Switcher

[RaceDriver205]

Alright all. Just finished an RF transmission system the other day. It uses 433MHz modules and ATTiny13s, and has enormous range.
I figured this could easily be adapted for switching on 4 separate effects from afar, so enjoy.

http://www.geocities.com/race_driver205/rftranceiver.pdf
(Note: geocities has 4.2MB/hour download limit, and file is 0.5MB. You might need to wait your turn  )

[RaceDriver205]

Surely someone must be interested in this? Lots of people have asked about remote switching before...

[Chuck]

I'm soaking it in. 

[Dave_B]

I just discovered this.  I've been looking for something to launch model rockets.  This is 80% what I need.  Now to find a U.S. distributor...

Thanks RM!

[RaceDriver205]

You can launch from about 200 meters away if you like 

[Conguito]

It's possible to modify this circuit to transmit/receive audio signals?
Salu2.

[Chuck]

I think the reason they don't use RF to launch rockets is the effects a stray signal may have.
Unless of course you don't care if it goes off without warning, whenever it wants.

And I think you can get em at www.sparkfun.com or Mouser.

[RaceDriver205]

It's possible to modify this circuit to transmit/receive audio signals?

No

I think the reason they don't use RF to launch rockets is the effects a stray signal may have.
Unless of course you don't care if it goes off without warning, whenever it wants.

Yeah thats a good point. I doubt it would happen, because the receiver checks the incoming signals are valid.
But that said, a hard wired connection is still the safest.

[hgamal]

What about to send midi messages, is it possible?

[Dave_B]

You guys are right, it wouldn't be safe enough to have a single signal.  My plan has been to use an AVR on either end, one generating an FSK or binary combination (I obviously haven't looked at the data sheets that closely) while the receiving end verifies it.  Here's another U.S. source for 433mhz modules. 

As an aside, adding "robotics" to my AVR-related Google searches really seems to clean up the results.   

[RaceDriver205]

What about to send midi messages, is it possible?

Yes possibly, but im not sure how midi signals work.

Here's another U.S. source for 433mhz modules. 

You might want to check these guys out: http://www.xenon-tech.com/index_ecat.php?cPath=10. They've got paypal.

You guys are right, it wouldn't be safe enough to have a single signal.  My plan has been to use an AVR on either end, one generating an FSK or binary combination

Thats pretty much how my tranceiver set works. It sends 4-bit words, with a start signal pulse (of set width) before each word. Instead of having the receiver output the word, it could simply check the word is correct (say 1011), and then activate 1 output. Odds of a misfire wouldn't be much greater than with a hard-wire.
As I remember, the word length can be extended to 8bits.

[Chuck]

MIDI messages are 8 bit.  MIDI commands may use 1-3 messages, or even a nibble of less then 8 bits.
But the basic message format is 8 bits.  So it should work.  One direction of course.  For MIDI send and received you'd need two transmitters and two receivers.

[Dave_B]

One of the 433mhz receivers I've read about is limited to 2400 baud (vs. MIDI's 31250), so you'd probably want to check that before you buy something for MIDI transmission. 

[hgamal]

MIDI uses 31.256 bits/s transmission rate. Is it possible to transmit data using this rate by 433 MHz radio?

[Chuck]

No, you'd have to slow it down to the 2400 baud -- buffering messages in the AVR.
If you're just using it for a switcher it probably won't need any buffer. 

For something like a keyboard, which sends notes, you get the following:
2400 baud is 2400 bits per second.
Using two 8-bit messages per note, you could send 150 notes per second.  Which is wicked fast playing. 

Overall if you didn't have a lot of midi clocks, multi synths, and a band transmitting MIDI all at the same time you'll probably be ok with a simple buffer.

In theory anyway.

[RaceDriver205]

No I would say this is not appropriate for MIDI transmission. There are other more sophisticated digital modules for these speeds.

[Chuck]

Like which module?

[RaceDriver205]

Perhaps "ZigBee"

[hgamal]

I think 2400 bits/s is adequate for control messages like program change. Maybe Controller events like expression pedal or volumes could be sent by this method!

[Dave_B]

I think 2400 bits/s is adequate for control messages like program change. Maybe Controller events like expression pedal or volumes could be sent by this method!

From what I've seen, controller events are typically pretty data intensive.  Is the idea to have all the effects at the soundboard, or are we just talkin?