What I've learned this month on the forum.....

[gringobomba14]

So I have limited the actual data sent, INCLUDING SYNC bits to about 20 chars long. It works perfect over short distances (10 cms) and long distances (almost 80 meters). I am happy to share my experiences with anyone who is interested, newbies and experienced peeps alike

[skimask]

So I have limited the actual data sent, INCLUDING SYNC bits to about 20 chars long. It works perfect over short distances (10 cms) and long distances (almost 80 meters). I am happy to share my experiences with anyone who is interested, newbies and experienced peeps alike

Also (and again, this is just my happenings with the modules and set up that I'm using), for some reason, I don't know why, and quite frankly, I don't care...
If I send my data at 2400, it fails the vast majority of the time. 9600 passes about 95% and my modules are supposed to max out at 4800. 19,200 baud (WAY above spec) passes about 75% at around double the distance.
Again, don't know why, don't care, just know it works out that way.
So, you might want to play with the speed a bit, see if you can get longer distances one way or the other.

[gringobomba14]

I have found that at 2400 and 4800 I get between 75 and 95 % first pass rate, as long as it's inverted. 1200 and 300 I may as well give up, and 9600 was only about 50% first pass rate. I'm now using FM modules, which I found to be much cleaner than the AM modules I bought, although I can use both with the program and get the proper data on the screen now...just takes a few seconds longer while I wait for a "good" transmission

[gringobomba14]

In the cold light of day I might just "play" with the baud rates and see if increased speed = increased distance.
What modules are you using Ski??

[dhouston]

Yes, manchester encoding works but there are simpler methods for sending short data bursts which work better.

Sync bytes are a lousy idea. See the screenshot at http://davehouston.org/rf-noise.htm (the bottom of the page) to understand why.

A single, wide pulse acts both as a start-of-frame indicator and to set the receiver's AGC and dataslicer threshold. See the screenshots at the top of the above cited page for an example.

Byte balancing sends each byte twice with the second byte a bitwise complement of the first and immediately following the first. This addresses the dataslicer threshold drift noted by skimask and gives you built in error checking - if the two bytes do not sum to $FF there's an error. Leaving a fairly long gap between data bursts allows the receiver AGC to reset. You can see its effects in the slope of the pulse in the screenshots on the above cited page.

I've provided an example in the Code Examples forum. X-10 has used the NEC protocol for its RF devices for over 30 years. Even Philips, which uses manchester encoding in all of its protocols, prefaces them with a long pulse to denote start-of-frame.

One thing you haven't learned yet is to

put your code
     in a form
that is more
     readable

[gringobomba14]

That is a very interesting page Dave, and one I will be visiting again and experimenting with ASK and FSK. Just out of curiosity, ASK seems more like AM and FSK seems more like FM, but with logic 1's and 0's instead of Casey Casum and the like....would this be correct?

 I wonder does this work

[skimask]

In the cold light of day I might just "play" with the baud rates and see if increased speed = increased distance.
What modules are you using Ski??

For one, the TWS/RWS-434 modules from www.Rentron.com
Others, I've gotten from www.sparkfun.com, the 434 TX/RX pair (don't remember the model # of the top of my head)
They're practically identical. I usually add them into an order as an after thought to keep a couple extras on hand.

[dhouston]

The one's from Spark Fun do not have an analog (i.e. linear) output. That's not much of an issue unless you want to measure the received signal strength.

The TWS/RWS (Wen Shing) are available from many dealers worldwide and have been cloned by several manufacturers.

Here's another, dirt cheap, source. [url}http://www.e-madeinchn.com/Product.htm[/url]

ASK (Amplitude Shift Keying or On Off Keying) is AM and FSK (Frequency Shift Keying) is FM. Most FSK modules cost more but you can use their Carrier Detect pin to tell when a signal is present, doing away with any need for sync bytes or start-of-frame pulses.

Range (i.e. distance) is independent of baud rate and is almost 100% a function of transmit power (severely limited by the FCC) and environment. It is, however, easy to increase range by improving the receiving antenna, adding preamplification, etc. Some receivers (e.g. the dirt cheap ones above) cannot handle a preamp, others (e.g. Wen Shing) can handle 2-3 cascaded.