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Old Dec 20, 2008, 07:55 PM
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another DIY 2.4GHz RC system using Cypress CYRF6936.

[edit]
if you want to skip straight to this project's current status update, go here:
http://www.rcgroups.com/forums/showt...1#post15262325
[/edit]

hey guys,
so there are a few DIY RC systems out there but i thought it would be worth making a few notes on my version.
the main difference with mine i guess is i'm using a Cypress CYRF6936 based RF module.

at the moment it is a fully functional RC system but future versions of the firmware will give it 2 way capabilities allowing sensor data to be returned from the aircraft.

full building instructions including circuit diagrams and microcontroller code are here:
http://sites.google.com/site/mrdunk/

one of the problems i found with the CYRF6936 is the lack of example code out there showing how to configure the modules. hopefully my documentation will help with this.

i'd appreciate any comments on either the RC system or ways to improve the documentation.


dunk.
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Old Dec 20, 2008, 09:08 PM
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This is cool! Would be great if it could be made Spektrum compatible so that the tiny receivers could be used. Might make a good addition to the Microstar2000 encoder.

Your robot is pretty cool too!
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Old Dec 21, 2008, 11:45 AM
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Hell mrdunk,
What can I say: very nice work ! It is always cool to say a new DIY RC systems, especially when he brings new ideas also.
Many questions:
I suppose that you made a PCB for the AVR2561. It must be tough to solder this kind of chip (small)?
Do you have an idea of the resolution of the stick of the sony PS2 ? I even thought that those sticks was not analogic..... don't know why.
Your choice about the Cypress CYRF6936 is interesting. You transmit at 250Kbps , that's a lot. I looks that you experience no problems at that speed. Cool !
And you did the mixing in the receiver.
Well done.
Olivier
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Old Dec 21, 2008, 01:01 PM
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I can tell you that those sticks are 10k ohms and that you get a full range in the motion allowed, about 100 ohms to about 9.6k ohms pushing the stick from one side to the other. So it is up to the microcontroller to get the resolution, but it is more than 512 counts for the PS controller
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Old Dec 21, 2008, 01:44 PM
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Quote:
This is cool! Would be great if it could be made Spektrum compatible so that the tiny receivers could be used.
hi Village_idiot,
thanks!
so i presume from your comment the Spektrum system uses the CYRF6936 as well?
so if this is the case then my hardware would be compatible with theirs but it's the firmware that is the big challenge on a project like this.
it would be easy to work out what RF channel their equipment was working on but the exact configuration would take a lot of time.
the CYRF6936 has a lot of possible configurations so finding the correct combination would be time consuming.

i'm not saying it's not possible, it would just take a while.
to be honest, i'm not really interested in having a conventional RC receiver on my aircraft. i want to be able to process sensor data and receive transmissions from the plane which a standard receiver would not allow.


Quote:
What can I say: very nice work ! It is always cool to say a new DIY RC systems, especially when he brings new ideas also.
hi Obor,
thank you!
i still have a long way to go but it's nice to have something i can use to have fun now.

Quote:
Many questions:
good. i like questions they make me think about the design decisions i have made.

Quote:
I suppose that you made a PCB for the AVR2561.
yes. the Eagle PCB files are in the download link off the main documentation site.

Quote:
It must be tough to solder this kind of chip (small)?
soldering surface mount components is actually surprisingly easy. there are a few good online tutorials including a few Youtube demonstrations.
the hardest part is making your PCB. i use the Toner Transfer method. it's actually described in a thread on this forum: http://www.rcgroups.com/forums/showthread.php?t=616909

Quote:
Your choice about the Cypress CYRF6936 is interesting. You transmit at 250Kbps , that's a lot. I looks that you experience no problems at that speed. Cool !
you can actually go up to 1Mbps with this chip but to do that you need to turn off a lot of the other useful features. (built in error checking, etc.) 250Kbps is more than fast enough for this application.
Quote:
And you did the mixing in the receiver.
hehe. yes.
i've been thinking this over since reading your 2.4GHz thread.
i definitely want to be able to mix on the receiver so the aircraft can keep flying on sensors without input from the controller but i have been coming round to adding the ability to mix on the controller as well.
if i allow mixing at both ends it allows the user more flexibility and it dose not add much complexity to the code.
so, it is decided. mixing at both ends.


i've been building an LCD monitor to plug into the Controller's UART today so i can view output from the Controller when i start playing with 2 way communication.

thanks for the comments,
keep them coming.

dunk.
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Old Dec 21, 2008, 02:06 PM
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oops. forgot to answer one...
Quote:
Do you have an idea of the resolution of the stick of the sony PS2 ? I even thought that those sticks was not analogic..... don't know why.
the PS2 controller sends each axis to an 8 bit register so decoding the PS2 controller SPI packet you get 0-255.
if you actually broke the thing open and connected the pots to microcontroller I/O you might get better theoretical resolution but the sticks are very short you wouldn't get much extra precision.

it's worth noting in my experience there is a huge difference between genuine Sony PS2 controllers and fake ones.
the Sony ones are analogue all the way through their range.
the fake ones have a large dead zone in the middle so you have to deflect the stick 10-20 degrees before you get a change in reading.
this migh not be true for all fake ones but it was for the 5 or 6 different makes i borrowed for testing.


dunk.
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Old Dec 21, 2008, 02:24 PM
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The walkera miniature helicopter receivers have a CYRF6936, and an ATMEGA 48, already assembled on a tiny pair of PCB's with a gyro sensor and mosfet's for two brushed motor controls for $33, so I bought an extra to play with... just need to get the right programmer setup. What's even more interesting is that they have one with two linear stroke servos for I think $40... If we could come up with an open firmware for that which was DSM compatible and could trivially be changed for things like mixing, extra on/off switches, extra servo outputs (or for brushless esc) using or ignoring the gyro, etc that would seem to take what's been done in the way of building indoor planes around the parkzone/vapor bricks to a whole new level. Plus firmware projects are a lot easier to distribute on the net and get into than community hardware is.

Not to say that there wouldn't be a market for a PCB with the cypress, larger micro, and a power amp to permit bidirectional communications too - I think there would be. But distributing a PCB is a whole other level of complication. There's an interesting service at www.seedstudio.com for community pcb projects, but it's not immediately apparent that they have the kind of thin pcb stock that would be desired for flight hardware.
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Old Dec 21, 2008, 05:37 PM
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Yes the Spektrum system uses the Unigen module in the TX and the RF6936 in the receivers. They also use 2 channels at the same time. And if that isn't enough, there exists a full time hopping DSMJ system made for Japan only, I assume it uses the same components.
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Old Dec 21, 2008, 06:29 PM
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Is the Spektrum "On-Air" data encrypted?
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Old Dec 21, 2008, 07:09 PM
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Probably not.
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Old Dec 21, 2008, 07:18 PM
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If that IS the case, then Spektrum compatibility is a distinct possibility. Have you, or theSteve, been able to confirm this?
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Old Dec 21, 2008, 07:28 PM
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Originally Posted by rmteo
Is the Spektrum "On-Air" data encrypted?
Probably not, however it is effectively "scrambled" by a code sequence to make the spreading work. That's not necessarily a big secret - Walkera for example uses one of the suggested code sequences from the cypress data sheet. The code sequence does have to have the right properties, so you can't just pick anything. But since that's a function of the cypress chip configured by writing to a defined register, it should be easy to figure out with an SPI bus monitor...
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Old Dec 21, 2008, 07:38 PM
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I was not referring to the chip spreading codes - that part I understand. As long as they do not employ some form of data encryption (such as AES available in the XBee for instance), then it is good.
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Old Dec 21, 2008, 07:54 PM
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I don't remember seeing encryption as a feature in those chips, and I doubt that the Cypress MCU has enough horsepower to generate the encryption.
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Old Dec 21, 2008, 08:00 PM
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It's kinda hard to say if the Cypress MCU has the power to perform the encryption - or not. The XBee's use an 8-bit Freescale MCU.
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