wireless propeller-to-propeller communication question
RobertW
Posts: 66
Hello,
I am collecting ideas about communicating between propellers (maybe 3-4) wirelessly.··I have in mind creating a 'network' of 'vehicles'.· The vehicles would communicate with a base Propeller which would give out commands.· I am thinking this would be contained within an area about the size of a typical room or smaller.· I don't believe that the amount of data being sent would be that great (go forward, speed up, slow down, stop, etc.)· I see that there is an object for Xbee modules.· Has anyone used this object or have a suggestion for a different wireless setup?
Thanks,
-Rob W.
I am collecting ideas about communicating between propellers (maybe 3-4) wirelessly.··I have in mind creating a 'network' of 'vehicles'.· The vehicles would communicate with a base Propeller which would give out commands.· I am thinking this would be contained within an area about the size of a typical room or smaller.· I don't believe that the amount of data being sent would be that great (go forward, speed up, slow down, stop, etc.)· I see that there is an object for Xbee modules.· Has anyone used this object or have a suggestion for a different wireless setup?
Thanks,
-Rob W.
Comments
I would encourage you to encourage Parallax to develop their semi-announced Wifi module. Using a WiFi module will (should) ensure robust communication at an acceptable rate.
If your need is immediate, then the wait and see Parallax Wifi module may not work for you. I am going to wait and see.
I've had enough of Bluetooth (very robust, but other problems exist) and have read enough about Parallax RF to realize it is not for me or my application.
--Bill
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You are what you write.
Ultrasound has a bit more range I think, it goes around walls, but same bandwidth.
Regular sound is retro-futuristic, let them all beep at each other like R2-D2.
Dumb question but does infrared need to be line-of sight? I'm assuming yes.
There are similar modules from HAC (via places like Sparkfun) www.sparkfun.com/commerce/product_info.php?products_id=560 or Hope www.microzed.com.au/Rf433.htm
That last link is in Australian dollars so you get a bit of a bonus when buying in US$.
There are many single transmitter and receiver units around. They all work, but they may have different supply voltages, (eg 12V on the Tx with 5V for data). Also they have no error correcting and the range is often far less than the data sheet says eg 10 metres for "50 metre" units. That could be because units are tested in free air 2-3 metres above the ground and that is very different to 10cm above the ground in a house with metal objects around.
Another problem with individual units is you need two antennas. And also the receivers are relatively deaf. eg -93db vs -121db for the transceiver modules above. db can be deceptive and if my maths serves me right, the difference between these two numbers is more than 500:1. This is important because all of them are limited to about 10mW on the Tx by law (in most countries) so the only way to get the range is to increase the receiver sensitivity. (There are higher power Tx modules but above 100mW they tend to reset LCD displays and propellers including changing random bytes in memory. Not fun to debug those errors!)
All-in-one transceiver modules have error correcting and if you send serial data in one end, it comes out exactly the same the other end. Those individual Rx and Tx modules (many of which may be only $2 each) transmit serial data faithfully, but when you turn off the transmitter, the receiver then faithfully listens to the white noise left over from the big bang. So you have to have some sort of clever filter on the Rx side to tell the difference between random fluctuations and a valid start bit for a RS232 stream. It can be done, and there is a code object posted recently that decodes sine waves for a 'modem' and also dtmf. But it all can get very complicated and chews up a lot of code space and development time.
These 'all in one' transceivers are about $25 each including the antenna.
Xbee works but my eyes glaze over whenever I try to decode the instruction manual. In contrast, the 'all in one' transceivers (which have onboard microcontrollers) generally have only 4 wires to connect - Rx, Tx, 5V and Gnd. What goes in comes out the other end. Most also have a choice of RS232 or TTL voltage levels so you can choose which one suits you. TTL 5v/0v will interface to a propeller with the standard 1k resistors. Then just use standard serial code objects at either end.
My personal preference is RS232 and to use standard D9 connectors. Even though there are more components needed (lots of max232s) and you only use 3 of the 9 pins on the D9, it makes debugging a lot easier as you can swap easily between wireless and wired connections. Debugging can take a long time, and if comms don't work wirelessly, the first thing to do is to replace the wireless with a wired link. With RS232, when all else fails you can plug it into a PC serial port and run a terminal program to see what is actually going in and out.
Finally, there is the buffer size. Most use 32 bytes and some use 64. I am experimenting with file transfer, ultimately with a view to transmitting pictures from mobile and fixed robots www.4dsystems.com.au/prod.php?id=76 and, not wanting to rediscover the wheel, I'm using the old-school file transfer protocol Xmodem. Xmodem needs 132 byte packets, and only the Yishi module can do packets that size (256 byte buffer).
If money is really tight, there may be scope to use those seperate Rx/Tx modules that are only $2-$3 each and write some clever spin code to detect white noise and then detect a valid start bit for a serial connection. This has been done in the picaxe world, eg by sending about 10 ascii 'U' characters (binary 01010101) first to synch the recevier. Such code would I'm sure be appreciated by many.
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www.smarthome.viviti.com/build
Post Edited (Dr_Acula) : 9/10/2009 4:04:57 AM GMT
http://www.semiconductorstore.com/cart/pc/viewPrd.asp?idproduct=42881
They are very easy to use and work very well. I have bought several dozen w/no complaints so far.
Even though it looks daunting it is pretty easy to solder wires to the pads for testing and breadboarding. It is also easy to solder them down once you get PCB's made too.
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BH
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www.smarthome.viviti.com/build
It would't be particularly fast, but it'd be neat!
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My Prop Info&Apps: ·http://www.rayslogic.com/propeller/propeller.htm
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For me, the past is not over yet.
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My Prop Info&Apps: ·http://www.rayslogic.com/propeller/propeller.htm
A network of vehicles doing that in the house is going to lead to a very quick divorce [noparse]:)[/noparse]
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For me, the past is not over yet.
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