Simple diy 2.4GHz - Page 4 - RC Groups
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Mar 08, 2008, 08:45 PM
Registered User
Happy programming in C ?

Uh, what's C ?

Just joking! No, I do not program with C, but, I have a
few friends that do ( and who owe me a favor )

But can you give me a guess-timate as to how much
time I would be asking for? I don't want to ask for too much.

Also, I have a different set of desires than you do as I
am only operating at a range of less than 2 meters.
But, if I loose control, I eat concrete or worse.

And 2 channels is all I need ( I would like a horn for fun! )

Anyways, here is a picture of the arm band transmitter
I cobbled up using an R/C car transmitter. The two finger
control device just uses the existing potentiometer from
the transmitter. It works very well and has been rock solid
as far as control goes. But, I have no way to control the
acceleration/braking rate and Let me tell you, when you are on that board and you hit the power a bit too hard,
it wants to spit you off the back! And if I hit the brake
just a wee bit too hard, it wants to spit me off the front!
So, that's why I want to "soften" up the control response.
I want it more like a gliding magic-carpet than a rowdy
low-geared, high compression, large displacement,
rip-snorter that it currently acts like!

Bob K
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Mar 09, 2008, 03:30 PM
Registered User
Bob, the work to put braking and acceleration limits on an already working system with these modules would be tiny. The application notes on the Jennic website do include two samples that could be easily modified to do this however I would not trust my teeth to them without some refinement. I shall publish my code soon, it is up to you to decide if it sufficiently teeth friendly . I'd point your friends at the Jennic website and get them to download the IDE/SDK. You've got me thinking about how I can usefully use this stuff on my electric bmx and reminded me of an old dream of mine to build a pair of electric shoes.
Mar 09, 2008, 06:33 PM
Registered User
Thank you Alan,

I am off to study the Jennic site.

Bob K
Mar 10, 2008, 03:15 PM
Registered User
So you have the 2 sticks controlling 4 channels? x and y axis on both sticks are working? I have stripped my controller and ordered a rx/tx.
Mar 10, 2008, 03:42 PM
Registered User
crazifunguy, yep I'm reading and sending all 4axis, currently I have left the controller electronics intact and read the joysticks and switches in the same way the ps2 would through a spi port. This only gives 8 bit resolution on the joysticks, you could connect the pots directly to the analog inputs of the module to get 12 bit resolution. I might well do this but keep reading all the buttons through spi.
Mar 10, 2008, 06:23 PM
Registered User
How are u getting all the extras transmitted? PWM?
Mar 18, 2008, 07:53 AM
Registered User
crazifunguy, all the channels are transmitted the same way, as serial data. The modulation and clever dsss stuff is all done for you by the modules, you just pass packets of data to it.

Can anyone recommend what value capacitors I should put across the receiver servo outputs? I cannot read the values off the receiver I have opened up!

Mar 21, 2008, 06:15 PM
Registered User
kevingill's Avatar
Fantastic work Alan, you must have put in a load of hours - it is very much appreciated.

These Jennic modules look good value even without the Zigbee built in! I noticed that they are also for sale here:

Is this the best module to buy? I guess that if I'm gonna play around with these things, I don't want to spend too much cash (save my money for some more lipos/beer). I'm used to progamming microcontrollers and PICs so these shouldn't be too difficult? (famous last words).

Also, is the downloadable free compiler OK? Are there any limits on the usage of the compiler?
Mar 21, 2008, 11:13 PM
Registered User
Hello Alan Hopper,

I invested in XPS but I am going to sell it back for its lack of redundancy. I read your earlier post where you said that you implemented an hopping sequence to avoid interferences. I am interested in building a system for my radio and implement it in my planes. Do you think you will share your code and your PCB schema with other people? I don't have much experience in coding, I used VB a little. Can you recommend any reading that I can do to understand better how to put a project like that together?

Thank you,

Le fou
Mar 22, 2008, 12:39 PM
Registered User
Kevingill, I picked these modules partly as they were the cheapest and partly as the processor seemed the most capable. My thoughts on other modules

xbee - proven by xps and a number of people on these forums - more expensive - bigger - all solutions seem to end up with an external processor

meshnetics - smallest and with good radio spec - more expensive - processor not as powerful - I may get one of these to see if it will interoperate with the jennic modules

Telegesis - similar in size to jennic - less powerful processor - more expensive - the ember em250 chip looks a good option for a micro rx

The free compiler and ide are not in anyway restricted and I have had no probs with them, there is a facility to do in circuit debugging over the serial port but I havenít tried it. There is no emulator which is a shame

Le fou, I shall share my code and pcb stuff. It is my first attempt at designing pcbs so I shall post them as soon as I have something in the hope of some constructive criticism!

I am working on a hybrid hopping scheme that I shall write up soon.

Alan Hopper
Mar 22, 2008, 04:08 PM
Trying To Takeoff
salat's Avatar
Originally Posted by Alan Hopper
The free compiler and ide are not in anyway restricted and I have had no probs with them, there is a facility to do in circuit debugging over the serial port but I havenít tried it. There is no emulator which is a shame
Alan Hopper
Alan, I'm sorry, can't understand what you mean about ide and tools. What compliler and tools you are going to use?
Thank you,
Mar 22, 2008, 05:22 PM
Inciting Riots
village_idiot's Avatar

Integrated Development Environment

Commonly text editor, compiler, linker, loader, simulator.

Think like AVRstudio for the AVR MCUs.
Mar 24, 2008, 10:53 AM
Registered User
I am using the free compiler and tools from jennic the tools include flash programming software that only needs a logic level serial connection to the modules. If anyone is looking at this stuff I recommend downloading every user guide, datasheet, reference manual, reference design and application note from the jennic site as info is rather spread around. The api details are spread over a number of reference manuals. This is also useful
I have been tweaking the servo output code and it is now clock perfect, so the only jitter is that due to the crystal. Still with upto 21 outputs.
Mar 28, 2008, 02:39 AM
That tree again!!!!
thanhTran's Avatar
Hi Alan

Great work you've done! Thank you very much for the inspiration and for the wealth of information. I have a few questions on the modules and their capabilities.

96KB RAM seems to be a lot but I'm wondering how much we have left for our application?

Do you use an external flash memory to store your code? or do you have to load it to the module every time it's powered up? It's kind of odd to see a micro controller with no flash nowadays.


Mar 28, 2008, 04:23 AM
Registered User
the modules incorporate a 128kbyte flash chip. At startup it automatically copies the program to ram. This happens very quickly, I think it only copies as much flash as there is program. The top 32k of flash can be used for whatever you like. You can connect external flash and have it load from that. The bin files for my current programs are about 11k so there seems to be plenty of space. There is a large on chip rom that I believe holds most of the api stuff so most of the ram is available(I think!).
Last edited by Alan Hopper; Mar 28, 2008 at 04:33 AM.

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