Author Topic: A schematic of a 2.4 Ghz Transmitter/Receiver for a remotely controlled bot.  (Read 5294 times)

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Offline AfsarTopic starter

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I have been searching online for more than a month now, but I do not seem to get any closer to solving this problem. The problem which I am facing is thus.....
During any RC robot competition there is a certain possibility (although unlikely) that two teams might have the same frequency which they use to operate their robots. After a long search online I have been led to believe that at frequencies of the range of 2.4 GHz the possibility of such a clash is non-existent and furthermore all remote control joysticks working on these frequencies are pre-programmed in such a way that once the connection is established, there is practically no noise interference. Now, if I buy one of these joysticks I might have no problem, but firstly; I am unable to find any of these joysticks in my city, so I'll have to order online and wait; secondly the prices for these I have found are way above what I can afford (since I am a student).
You might say the next option is to wait and save some money or raise some of it, since the competition for which I am preparing is in January I do not have a lot of time to save and what I could raise can only get me either the Joystick or the other components for the bot.

So if you can help me build my own transmitter and receiver module before the 18th December, I would be indebted to you. I am not a complete novice but neither am I an expert. Any help would be gratifying.

Offline AfsarTopic starter

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I am using Proteus-Isis(latest version) for simulation of various circuits and VMlab with WinAVR to code the microcontrollers. I have purchased a USB programmer for Atmega8, which I hope would suffice. I will be using a plane circuit board and soldering components onto it according to the circuit diagram which you provide(hopefully), but only after simulating it.

Offline Admin

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If you are using a remote control:
Just buy several different frequency crystals for your remote control. There will be a number on them, and just make sure it doesn't match with that of your opponent.

Any well run competition confiscates remotes from all participants who aren't competing to avoid interference.



If you are using a microcontroller:
2.4GHz is just a frequency. Today, electronics uses fancy algorithms that go way beyond a single frequency.

For example, Bluetooth does what is called 'frequency hopping'. It actively looks for noisy channels and then avoids them, often transmitting data on 2 or 3 frequencies at the same time. I've found Bluetooth to be *extremely* resistant to interference.

But it's not something you can just throw together in a few days with resistors and capacitors. You have to buy a module for it.

Don't however use Xbee. They are very susceptible to interference.

I also sell a microcontroller with built-in Zigbee wireless:
http://www.societyofrobots.com/axon_mote/

It uses the same Zigbee technology as the Xbee, however you can program it to do frequency hopping and noise analysis like Bluetooth. It won't be as resilient as Bluetooth, though. So why use it? Well, unlike Bluetooth, you can link up as many as you want to form a mesh network.

But since you only have 5 days left until your 18th deadline, I recommend finding a Bluetooth transceiver.

Offline Soeren

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Hi,

So if you can help me build my own transmitter and receiver module before the 18th December, [...]
A very experienced HF engineer with all the instruments needed might just be able to do it in a week (if he didn't sleep and only made very shallow initial tests).

Anyone not being an experienced HF engineer should go buy a working unit (which the HF engineer would as well, unless he was making it for production or just had a very Masochistic perspective on life in general).

Even if I gave you a schematic, your chances of getting it to work would be less than one in a million - HF and especially the top of the UHF band is definitely not a cakewalk - lots of seasoned EE's would not take that route and modules can be bought fairly cheap. But don't go for the cheapest Made in China stuff - they are generally hopelessly overrated on range and sensitivity.
The cheap 433HMz modules from Seed Studio are extremely crappy and they keep on excusing for the lack of documentation - they used to claim range to be 100m, but every other 433MHz transmitter I have, like eg. a doorbell ranged to 25m max. are more powerful than the Seed Studio transmitters. If I transmit with the Seed Studio TX at 10cm and the doorbell at 50cm, the doorbell signal alone goes through (and it's not just a single flawed transmitter. A friend and I bought a load of them and they're all crappy). 2.4GHz is even harder to work on, as even breathing on the PCB will change its behaviour.

The morale of this is, that your best option is to buy a complete ready made R/C set (which you can get a demo of before paying), as it takes lots of instruments and experience to get crappy stuff working and frankly, those Seed Studio modules may never see service, as it simply isn't worth the time to get them to perform better.
Regards,
Søren

A rather fast and fairly heavy robot with quite large wheels needs what? A lot of power?
Please remember...
Engineering is based on numbers - not adjectives

 


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