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Author Topic: hope RFM12  (Read 2096 times)

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Offline WebbotTopic starter

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hope RFM12
« on: June 24, 2010, 10:48:43 PM »
Wondered what you folk thought of this device http://www.sparkfun.com/commerce/product_info.php?products_id=9582

Very cheap

Am thinking it could be used in swarms to xmit position to other robots - or even as a cheap link to PC

First came across them in Elektor magazine over a year ago and another member has resurrected them for WebbotLib. Cheap'n'simple but quite a complex command set.

NB Sparkfun only seem to sell the strange form (SMD?) of the device, whereas I think that HopeRF, the manufacturer, also sell a DIP/DIL format


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Offline dunk

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Re: hope RFM12
« Reply #1 on: June 25, 2010, 02:41:04 AM »
>100m range,
115.2 kbps,
$6.95.

on paper they look like excellent value.
i can't remember seeing another transceiver that gives anything like that performance for the price.
(most of my research has been for longer range devices though.)

any feedback on RF link reliability?


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Offline waltr

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Re: hope RFM12
« Reply #2 on: June 25, 2010, 07:28:47 AM »
They look nice. Just remember that all the communication protocols must be done by the user's code.

Offline amando96

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Re: hope RFM12
« Reply #3 on: June 25, 2010, 08:41:16 AM »
I've tried using those, really hard, dunno if it was just me, but i wasn't even able to configure them.
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Offline WebbotTopic starter

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Re: hope RFM12
« Reply #4 on: June 25, 2010, 10:40:35 AM »
The Elektor article gave some software examples and I was also to look at this http://www.das-labor.org/wiki/RFM12_library/en
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Offline TrickyNekro

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Re: hope RFM12
« Reply #5 on: June 25, 2010, 01:01:04 PM »
Most of RF communication protocols (the easy ones at least) use Manchester coding...

Wikipedia it... it not that hard....


The original encoding is an XOR.... On Clock and Data lines....

The differential coding as the name suggests is a subtraction.... (Clock - Data) = Signal

Manchester encoding is a nice one... You can get both data and the baud rate from the signal...
Yes, if your code is good enough, it can self sync.... Nice nice one :-D

Decoding is also easy enough... Provided the signal is synced... You can get the data....
In original Manchester encoding to decode the signal you to:

Read the transactions of the signal on the clock...

If the signal is at the high rail and in the beat clock it turns to low rail it's an 1
if the signal is at the low rail and it the beat clock it turns to the high rail it's a 0

You can also retrieve the clock frequency from the signal, just don't know how....

And I don't know how to decode differential Manchester...


So... that's basically it....
You have to dedicate a microcontroller to the chore.... Not that it's really necessary but it's comfortable ;-)
For whom the interrupts toll...


P.S. I've been inactive for almost a year... Don't give promises but I'll try to complete my tutorials. I'll let you know when..

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Offline WebbotTopic starter

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Re: hope RFM12
« Reply #6 on: June 25, 2010, 06:44:03 PM »
Tricky - you are talking generics. What amando refers to is the vast amount of configuration options on this particular device and trying to find the correct settings for comms to take place.
Hence my reference to other libs, examples that have working examples
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Offline TrickyNekro

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Re: hope RFM12
« Reply #7 on: June 26, 2010, 12:55:55 AM »
Tricky - you are talking generics. What amando refers to is the vast amount of configuration options on this particular device and trying to find the correct settings for comms to take place.
Hence my reference to other libs, examples that have working examples

Yes... I'm just saying you can try Manchester coding for on air transmition... I had in mind that this IC has a complex instruction set.... 

Still... I just made a simple proposal... Not necessarily replied to anyone...  ::)
For whom the interrupts toll...


P.S. I've been inactive for almost a year... Don't give promises but I'll try to complete my tutorials. I'll let you know when..

Cheers!

Offline dunk

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Re: hope RFM12
« Reply #8 on: June 26, 2010, 06:28:11 AM »
Yes... I'm just saying you can try Manchester coding for on air transmition... I had in mind that this IC has a complex instruction set....

hi Tricky,
sorry but no.
Manchester Encoding is used to address a completely different set of problems.

if you have a transmission system with an unknown reference level Manchester Encoding is a good choice.
for example with the long cable lengths involved in 10BT ethernet the reference voltage (0V) can vary quite a lot between devices.
because Manchester Encoding looks at the changes in voltage rather than the set level of a voltage it can handle the unknown reference voltage.

Manchester Encoding is sometimes required on more old fashioned RF systems but usually it is handled behind the scenes on all the newer ones. (i doubt if there was ever a transceiver system that required you to implement it your self.

the RFM12 already does all encoding for you in the background using FSK. http://en.wikipedia.org/wiki/Frequency-shift_keying
implementing your own Manchester Encoding as well would just cut your bandwidth in half.


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Offline TrickyNekro

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Re: hope RFM12
« Reply #9 on: June 26, 2010, 07:58:00 AM »
the RFM12 already does all encoding for you in the background using FSK. http://en.wikipedia.org/wiki/Frequency-shift_keying
implementing your own Manchester Encoding as well would just cut your bandwidth in half.


dunk.


Opps... Didn't knew that... My bad... :-/

I just had in mind some old 433 modules (without on board encoding) that some guys at another community have used using this encoding to get
the trash out...

My bad, my bad....  :D :D :D


AAaahhhhhhh.... I'm getting old... :-/
For whom the interrupts toll...


P.S. I've been inactive for almost a year... Don't give promises but I'll try to complete my tutorials. I'll let you know when..

Cheers!

Offline Marky

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Re: hope RFM12
« Reply #10 on: July 17, 2010, 11:12:05 PM »
Well. RFM12 Module is only a RF-end module so you need to program it with your favorable MCU. That company also provides demo codes which instructs you to configure the registers. If you are sophysticated programmer, it will be easy to master it quickly.

Certainly if you want to use modules with standard UART interface, you can consider to use Dorji applied technologies' module DRF1212D10 which works at very low current in receive mode (normal 3.2mA).

 


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