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433MHZ AM Radio Modules

:: EPE Chat Zone ­:: ­Radio Bygones Message Board :: » EPE Forum Archives 2010 - » Archive through 06 December, 2011 » 433MHZ AM Radio Modules « Previous Next »

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dave_g
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Post Number: 703
Registered: 05-2005

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Posted on Sunday, 06 November, 2011 - 08:33 am:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

This week I've been having a bit of a nightmare with these. I have both RF Solutions and Quasar types (actually the same company).

All I want to do is to send a very short piece of data (outside temperature) about 20m. So far six inches is a struggle!

I have designed and tested;

a) a bit bashed serial interface, works a treat with a direct connection but...

b) pulse width modulation, bit like a manchester code. Again, works a treat with a wired connection.

c) frequency shift keyed, again, perfectly accurate and stable on a wired connection but once the RF modules replace it, it all goes horribly wrong.

I'm now at a point where I'm going to leave it a week! I just wondered if anyone else had got something going without using a specialist IC. I have used PIC16F (old stock) so far and I'm determined to develop a robust bit of code that works.

I'm now wondering if the Tx and Rx being so close together is "swamping" the reciever.
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cjaysharp
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Post Number: 128
Registered: 06-2010

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Posted on Sunday, 06 November, 2011 - 10:14 am:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

http://www.winpicprog.co.uk/pic_tutorial12.htm
and
http://jap.hu/electronic/codec.html

were used as the base for a project I built a few years ago. Never completed it but the RF bit worked a treat to about 10 metres (probably further but I only tested that far) using some cheap end of line AM modules from Maplin.
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dave_squibb
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Post Number: 265
Registered: 04-2005

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Posted on Sunday, 06 November, 2011 - 01:22 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

"I'm now wondering if the Tx and Rx being so close together is "swamping" the reciever."

Quite possibly, easy to disprove though.

What are they mounted on? Stripboard or prototype breadboards can cause big problems.

Also good supply decoupling is essential with 100n or 10n.
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epithumia
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Posted on Sunday, 06 November, 2011 - 02:27 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

I've used the AM-RT4-433FR with reasonable success.

I use:
Logic 0 is a 0.5ms mark, 1.5ms space
Logic 1 is a 1.5ms mark, 0.5ms space
(When not transmitting, drive the transmiter input DC low.)

I see they quote the data rate as 50Hz to 9,600Hz.

They can't send DC: hence why I don't use mark for 1 and space for 0.

Typically I send a 16 bit code to identify the transmitter, then the data, then repeat the entire thing inverted for checking.

I never had trouble using breadboards or short range. A bigger problem is that range could suffer in the REAL world, when I didn't have all those long breadboard leads to radiate the RF!

Epi

(Message edited by Epithumia on 06 November, 2011)
If you need me, Neil and me will be hanging out with the Dream King. - Tori Amos
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dave_g
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Post Number: 704
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Posted on Sunday, 06 November, 2011 - 03:11 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

Cjay - I reckon I've got the same modules as you had, glad to hear they worked for you! The coding looks broadly similar to mine but with more leading "1"'s.

Dave - yes, I am using both of those in an effort to ensure it doesn' work...! :-(

However, I've removed the copper underneath the transmitter. The receiver is still on a prototyping breadboard. I have decoupled at 47uF and 100nf, will try again. One issue was that I was using my EasyPic5's power supply, which had lots of 100Hz noise. Using a separate supply has shown an improvement.

I will try resetting things up (cleared away now for the week ahead back at work) with the transmitter in the next room, or whatever, or at least a much greater distance away.

Epi - nice idea about inverting for checking. My latest (FSK) version uses pulse widths of 1ms, 0.5ms, and 0.25ms. I must try making the pulses a little wider to see if that improves.

Thanks for all your help, everyone, all ideas greatly appreciated. I'm writing the code in C, happy to make it available once proven!
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dave_squibb
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Post Number: 266
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Posted on Sunday, 06 November, 2011 - 05:49 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

http://www.rfsolutions.co.uk/acatalog/DS015-3_AM-RRQx.pdf

See notes on page 4
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cjaysharp
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Post Number: 129
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Posted on Sunday, 06 November, 2011 - 07:11 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

The pre-amble is important, it 'clears the decks' at the receiver, because the receiver is always seeing noise the level of the output drifts up or down and can corrupt your data if not 'reset' with a long enough pre-amble.
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dave_g
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Post Number: 705
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Posted on Sunday, 06 November, 2011 - 08:40 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

Dave, I am most certainly guilty re the Veroboard comments. I think I'll eradicate that.

Cjay - an interesting insight, I can easily make the preamble longer in my transmitter/sensor software.

I'll also add some more decoupling and check ripple.

The new test rig will make a greater distance between Tx and Rx.

I may also slightly reduce the speed of data to ensure no drop off at the top end.

That sounds like a plan, thanks all, much appreciated. In about a weeks time I may have positive news!
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wizard
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Post Number: 81
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Posted on Monday, 07 November, 2011 - 11:13 am:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

I use the RF Solutions modules AM-RT4 transmitter and AM-HRR receiver. They have been operating well for some time.

However, I did have problems when I first started using them, problems which appear to be similar to yours.

I was using 16F877s (yes I know they are old but I understand them and they work) to generate data and receive data.

When I connected the send and receive 877s together using the UART pins directly, everything worked alright. When I used the RF modules it didn't work.

After some head scratching I realised that the specification for the devices states "can be used to transmit data up to 4Khz". I had the baud rate set to 9600 which is 9600 bits per second which is 9.6Khz - way above the spec. I changed the baud rate to 1200 and everything worked.

Hope this helps.
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dave_g
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Post Number: 706
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Posted on Monday, 07 November, 2011 - 08:17 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

Thanks Peter, my data "frequency" is well below that but still on the upper edge, ish.

Interesting idea to use the UART; I'm using a PIC16F88 at the transmitter end and a PIC16F873 at the receiver end. You're right, they are old, but they do the job even if I have got the RAM on the 873 to 97%!
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bowden_p
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Post Number: 80
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Posted on Tuesday, 08 November, 2011 - 01:41 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

Hi Dave,
Do your problems with the wireless operation stem from the RF upsetting the operation of the PICs? Perhaps screening them from the Tx might help? ( I am guessing that the module is quite close to the PIC.) RF radiation from the digital side could also limit reception too.
Regards, Paul.
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dave_g
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Post Number: 708
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Posted on Tuesday, 08 November, 2011 - 09:38 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

Paul, interesting point that had not occurred to me. I don't think so, but when I separate the transmitter from the board it is currently mounted upon I should be able to eradicate that from suspicion.
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dave_g
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Post Number: 712
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Posted on Sunday, 13 November, 2011 - 06:06 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

Dear all,

A qualified success. So far, I have;

a) made my pulse times 1.6ms, 0.8ms, and 0.4ms
b) moved the transmitters and receivers about 1m apart (window ledge to bench!)
c) Ensured a clean supply for both
d) Lifted the transmitter off the veroboard and attached with flying leads, and added 17.5cm of wire as a quarter wave antenna.

I now have communication which is OK about half to three quarters of the time. This is without moving the reciever off the prototyping board.

The most significant changes were the antenna and some distance.

Next week I will now complete the transmitter so that is "ready to go" and work on the receiver.

Thanks for all your help - I will finalise some details (including code) and put it on CZ.
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dave_g
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Post Number: 713
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Posted on Friday, 02 December, 2011 - 06:03 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

An update...

Transmitter now working. The key with the "cheap" Maplin module was the right length antenna. I suspect it is part of the tuned circuit and therefore the module is rather vulnerable. I also moved it off the veroboard (as recommended by many, oh, and it's in the instructions!) and just stuck it to the side of the plastic enclosure with a sticky tab.

Removed my FSK software and gone back to simple pulses with a longer preamble. Just about there, I think. Time over the last few weeks has been a major challenge, but I am winning.

I have also managed to program, I think, in C a very complex formula to calculate degrees C from a thermistor resistance (i.e.) no lookup table.

Receiver still on breadboard for the moment.

More to follow...!

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