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PICList Thread
'RF modules, PIC 16F84, Rolling Code'
1998\12\02@055501 by Stephane Favard

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Hi to all,


Presently, I developping a RF Remote control using AUREL RFF Modules (433 Mhz) a
nd 2 PIC 16F84 for Tx and RX. It works just fine but I
would like implementing the Rolling Code.
I'm searching any informations about Rolling Code Algorythme.
Very thanks in advance if you can give me some links and (or) informations...


Stephane

For AUREL RF Modules, loook at http://www.aurel.it

1998\12\02@061208 by Tjaart van der Walt

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Stephane Favard wrote:
>
> Hi to all,
>
> Presently, I developping a RF Remote control using AUREL RFF Modules (433 Mhz) and 2 PIC 16F84 for Tx and RX. It works just fine but I
> would like implementing the Rolling Code.
> I'm searching any informations about Rolling Code Algorythme.
> Very thanks in advance if you can give me some links and (or) informations...

Microchip hold some patents for rolling code encryption. It
was developed by a South African company (Nanotec) and Mchip
bought it. Mchip calls it Keeloq.

Microchip have many application notes for the generation and
decryption.

Note that Mchip requires a NDA if you want to get hold of the
nuts & bolts. This also means that it is possible to break it
if you know some unscrupulous people willing to violate their
NDA with Microchip. For the record, I don't have any first
hand knowledge of the algorythm, nor am I interested in it.

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1998\12\02@101516 by Andy Kunz

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>Note that Mchip requires a NDA if you want to get hold of the
>nuts & bolts. This also means that it is possible to break it
>if you know some unscrupulous people willing to violate their
>NDA with Microchip. For the record, I don't have any first
>hand knowledge of the algorythm, nor am I interested in it.

They are VERY liberal with the code.  I have a copy, and did not have to
sign nearly as bad an NDA as I did for other things with Microchip.

FWIW, it works very nicely.  I ported it to a bigger PIC and changed some
items in it which were in violation of a patent for my customer (a bogus
patent, but it was cheaper for them to change Microchip's code than to pay
a lawyer <VBG>) due to the application (garage door openers).

The concept is pretty well documented in the source code they provide.  Go
for it!

Andy

==================================================================
Andy Kunz - Statistical Research, Inc. - Westfield, New Jersey USA
==================================================================

1998\12\02@114901 by Peter L. Peres

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On Wed, 2 Dec 1998, Tjaart van der Walt wrote:

> Note that Mchip requires a NDA if you want to get hold of the
> nuts & bolts. This also means that it is possible to break it
> if you know some unscrupulous people willing to violate their
> NDA with Microchip. For the record, I don't have any first
> hand knowledge of the algorythm, nor am I interested in it.

Just roll your own and delete the source file with the dictionary after it
all works. Let them look for it. Come to think of it, not even a law
enforcement agency could have you produce it afterwards ;)

Peter

1998\12\03@112534 by Stephane Favard

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Hi,

Can anyone tell what's the best layout for "on board" Emmitter RF antenna with
a 0.8mm dielectric board. It's a 433 Mhz RF module but I don't know impedance
(may be 75 ohms...). I heard that it's better to have a gnd plane side and the
antenna on the other side...


thanks..

Stephane

1998\12\03@125355 by Craig Lee

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Stephane,

Please see the application note on microstrip and antenna design
on the Linx Technologies website.  It has formula and description
of how to do just what you are asking for.

http://www.linxtechnologies.com


Craig

> {Original Message removed}

1998\12\04@040848 by Jochen Feldhaar

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Hi,
I would like to comment on the antenna problem.
At the moment I myself am designiing a somewhat similar system, and have
learned that the manufacturer chooses the output impedance so that the
transmitting power is maximized for the proposed operating voltage. This
gives about 300 Ohms. Therefore, a matching network is advisable, also for
filtering the output signal at the same time.

As to the form of the antenna: It is best located in "free space". A ground
plane next to the antenna is ABSOLUTELY not workable. The best design is to
have a loop or several loops formed like a spiral, the best form is to test
various sizes.

I hope this helps clear some problems...

Greetings
Jochen DH6FAZ

1998\12\05@084026 by Peter L. Peres

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On Fri, 4 Dec 1998, Jochen Feldhaar wrote:

> Hi,
> I would like to comment on the antenna problem.
> At the moment I myself am designiing a somewhat similar system, and have
> learned that the manufacturer chooses the output impedance so that the
> transmitting power is maximized for the proposed operating voltage. This
> gives about 300 Ohms. Therefore, a matching network is advisable, also for
> filtering the output signal at the same time.

This is interesting. It should be 50 or 75 ohms, for an open quarter wave
dipole ?! How did you determine the output impedance ? Remote power meter
or microwatt transmatch ?

> As to the form of the antenna: It is best located in "free space". A ground
> plane next to the antenna is ABSOLUTELY not workable. The best design is to
> have a loop or several loops formed like a spiral, the best form is to test
> various sizes.

I was going to borrow a TV service wavestrength meter / receiver and set
it up for 'free space' metering with a rubber duck at 3 meters distance
or so to get the antennas right. Did you do something like this ? Do you
have a method that works better ?

> I hope this helps clear some problems...

Yes ! Thank you.

Peter

1998\12\07@054507 by Jochen Feldhaar

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Hi Peter,

next mail to same guy...
I didn't design this beauty, but I was the guy doing the transmitting range
tests. But as I am a ham op, I would use a 70 cm transceiver for the
testing of transmitter efficiency. Also, I would adapt the LC matching
network for max electromagnetic field between transmitter output and coil
"antenna". A TV test receiver will give good results also...
Of course, the efficiency is almost proportional to the cross-section of
the loop, but in the application I had size was essential, not absolute
efficiency. So while designing, define your requirements of space, range
and transmitting power, and then cook a workable solution out of this.

Greetings

Jochen DH6FAZ

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