RF modules

crazynight

Senior Member
RF is totally new to me!

I am thinking of added RF to my project to send a 4x8 digit string to a 4x7 segment display it will be an add on to this http://www.picaxeforum.co.uk/showthread.php?25755-Read-Temp-and-display-on-a-sure-4x7-segment-display

Moving forward I may want to send the same string to multiple RX's are the RX/TX modules paired out the box? if I wanted 2 displays would I need 2 TX's or do all the RX's listen and receive all the 433 traffic?


I know they are sold as "433MHz Radio Transmitter and Receiver Pair" but the pair could be misleading me :confused:

on further search found http://www.picaxe.com/docs/axe213.pdf

but still left me puzzled...if they are paired how can they be 'point to multipoint'....HELP:(

The communications is also ‘point-to-multi-point’; anything sent by a transmitter
will be received by all receivers. Only one transmitter should be operated at a time
or communications may be unreliable and one transmitter may ‘drown-out’
another. The transmitter board has a ‘transmit enable’ connection which should be
used to enable the wireless transmitter module only when data is to be sent. This
minimises interference and complies with good radio etiquette.
 

Morganl

Senior Member
They are just sold in a set of transmitter + receiver, not techically "paired" in a sense they recognise each other specifically.

Buy several such sets, and any of the transmitters (but only one at a time) can send and all receivers within reach receive simultaneously.

That italic text is to the point.

You may also want to add a specific "key" to the message to recognise so the program connected to the receiver only act when message start with that key. Maybe also a checksum. For improved chance of receiving use preamble. (do a web search in transmit preamble).

1) enable transmitter
2) send preamble
3) key, node adress, whatever identification
4) data
5) checksum
6) end marker
7) disable transmitter

The you are a real pro!
However, probably you do not need half of it...

Start doing something really simple first, like just sending a character repeatedly and make sure you get it in the other end :)
 
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crazynight

Senior Member
They are just sold in a set of transmitter + receiver, not techically "paired" in a sense they recognise each other specifically.

Buy several such sets, and any of the transmitters (but only one at a time) can send and all receivers within reach receive simultaneously.

That italic text is to the point.

You may also want to add a specific "key" to the message to recognise so the program connected to the receiver only act when message start with that key. Maybe also a checksum. For improved chance of receiving use preamble. (do a web search in transmit preamble).

1) enable transmitter
2) send preamble
3) key, node adress, whatever identification
4) data
5) checksum
6) end marker
7) disable transmitter

The you are a real pro!
However, probably you do not need half of it...

Start doing something really simple first, like just sending a character repeatedly and make sure you get it in the other end :)
Thanks you answered all my questions and it all makes sense now. I guess if you wanted to use 2 tx's you would fit a rx to each Picaxe and monitor for traffic and only send if the coast was clear.....think I will keep to cables for this project.
 

Morganl

Senior Member
Nice to hear.
Yes waiting for coast clear would be a good idea.
A trick then is to make not all devices wait the same amount of time and then all send at the same time... use random delay, or delay based on some identification/adress/serial number.

I have seen advanced modules with onboard microporcessor that do work in pairs, so you use it like a cable, (with delays of course and possible signal loss etc... )
They were not particularly expensive, but i forgot where i saw them...


Ah, BTW, you need not quote so much, especially when answering generally to the post just above. To keep thread size down.
 

Morganl

Senior Member
Now i remember: i was looking at EWRF - 3022UT for a future project. (do a web search)

I think i also have seen 2,4 GHz modules carrying async serial over different protocols.
 

crazynight

Senior Member
Result discovered some of the old kit I inherited as part of this project has one of these http://www.yishi.net.cn/rf/ProductShow.asp?ID=195 and two matching TX's each are on boards with 20m picaxe's might be old but will save me some time.

Can potentially see why the old system was described as "had issues" as there is no way of timing the tx both could send data at the same time.
 
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