RF transmitter/reciever

[benji]

i just baught this thing to make wireless communication between pc and robot.
trying with this it seems like the reciever is always getting stuff even if the sender isnt sending ,,
the byte seems to be recieved better with lower baud rates,,1200 is the best
did anybody use this before? any reccomenations? any points to be aware of? ,, thanks

[Steve Joblin]

Can you tell us what RF Transmitter/receiver product you have?

[benji]

there is no english word written there, all chinese words,,lol , it only says in english that its a 433 mhz
and there is a place to attach an antenna, pins are for vcc ,gnd , data in ,data out

[superchiku]

the problem is u havent used a decoder or encoder ic with that , if u dont do so there can be many stray signals which may affect the receiver, its pretty easy to do with uart and decoders and encoders...

it is known as a 433 mhz rf transmitter and receiver module, very cool stuff and yes the baudrate of 1200 is best suited for this type of rf transmitting

[Steve Joblin]

does your transmitter/receiver look anything like this?  http://www.rentron.com/remote_control/TWS-434.htm and http://www.rentron.com/remote_control/RWS-434.htm
If so, you may find this write-up about using them with a Basic Stamp helpful about minimizing errors... http://www.rentron.com/Stamp_RF.htm

[paulstreats]

Also, I came across something the other day that may help, ive got some radio devices i havent used yet but while investigating, it seems that the receiver usually receives random bytes when nothing is being transmitted (because of natural interference). Its really messed up my plans for interrupt on uart receive though. Here is how somebody else managed to get around it by using controlled protocols: http://www.uchobby.com/index.php/2007/05/01/simple-rf-wireless-link/#more-42

There is also an idea for an accelerometer controlled mouse on the same website if anybdys interested (i think its a neat idea)

[superchiku]

as i told u bfore using encoders and decoders will minimize all interferences

[paulstreats]

The modules already have encoders/decoders built in. While they are transmitting there is minimal interference, its when the transmitter is not sending is when the interference occurs which you hav no control over. Its really an issue of building a data packet system with effective start and stop sequences so when data is received you can decide if its come from the transmitter or not. The only way to effectively use it for an interrupt on receive is to use an additional uc between the receiver and the target system

[superchiku]

i tested these modules bfore ,

an extra encoder decoder arragement like the HT12XXXX something can minimize all interferences

its recommended  that u use such modules with interrupts and extra encoder/decoder circuitry

[Admin]

I'd say your "thing" is of low quality. I've never got random noise from any of my transmitters.

Also, just a thought, I can create "stuff" in my signal by intentionally adding noise to the power supply. Are you properly regulating it (capacitors, voltage regulator, etc)?

[benji]

the noise is not from the transmitter, the problem is when the transmitter isnt sending anything , the recieve reads gibberish
so here creates a little problem if you use UART recieve interrupt,,cuz the reviever flag would always be set
,,i am not going to use interrupts myself but it also make a problem to know if the byte is real or its noise,, i think ill do solve it by software
its like before the transmitter sends real data it send A B N for example,, so when the reciever sees the A B N directly reads the next byte as real data and process it,,
any other ideas?

[Admin]

the noise is not from the transmitter

How do you know this?

Anyway, what I meant was, the transmitter and/or receiver could be poorly handling noise.

And if you don't properly protect them from noise, they will transmit/receive it. For example, you might not command the transmitter to transmit anything, but then it gets noise and then it faithfully transmits that noise.

I think my solution was a valid suggestion to attempt

[superchiku]

yes that can be a case but where from this noise is coming from even though he is not transferring anything, that may be due to external interferences Is any kind of radio station nearby your place of working??

[paulstreats]

errm, white noise just exists plain and simple.

any radio channel that isnt tranmitted over will be in a state of white noise, what happens is that when the receiver is on and the transmitter is off, the receiver is always picking up white noise. Because it is random it will invariably create the correct sequence of an ascii character from time to time at a range of all possible baud rates. When the transmitter is on, the power of its sending must be strong enough to overpower the white noise, this isnt usually a problem tho.. and even if it was, some kind of double or triple sending or ping pong sending will usually filter the noise out.

[karmax]

use as low as baudrate u can.AND IF U CAN USE LOW FREQUENCY THEN IT WILL BENEFICABLE FOR U .BECAUSE AS LOW AS FREQUENCY AS LOW IS NOISE

[benji]

thanks guys , ill consider everything uhave mentioned

[benji]

i did do it today and it works great at 2 meters range
i did take the transmitter circuit 10 meters away ,the signal wasnt good
sometimes it recieves the riht bytes but most of the time its gibberish ,,could be that due to short antenna?
i did us a copper wire as an antenna (30 cm long but all rounded up like a coil)

[GHF]

errm, white noise just exists plain and simple.

any radio channel that isnt tranmitted over will be in a state of white noise, what happens is that when the receiver is on and the transmitter is off, the receiver is always picking up white noise. Because it is random it will invariably create the correct sequence of an ascii character from time to time at a range of all possible baud rates. When the transmitter is on, the power of its sending must be strong enough to overpower the white noise, this isnt usually a problem tho.. and even if it was, some kind of double or triple sending or ping pong sending will usually filter the noise out.

This is definitely true.

I've been using a pair of RF-24G xcvrs. I configured the modules to use an 8-bit preamble, 8-bit device-dependent address, and 16-bit CRC calculated for a 4-byte payload, all set to be received at 1Mbps. Even with all these ways to verify packets, the receiver would still receive noise that passed for a valid packet every 30 or so seconds. I added another header byte to the payload, and that more or less made it work pretty well.

I never tested the range, but Sparkfun says 280 or 150 meters outdoors depending on signaling rate. It works well enough across a basketball court, though.

-Xo W.