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Interference problems or PIC problem?

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sysysy

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Hello everyone,

i use PIC16f877A USART to do my full duplex communication between 2 controllers....

Initially, i use jumpers, and the communication work well.
Then when i proceed this to RF modules (wireless communication)

then problem start occur. OK, since it is full duplex, so i use different frequencies of module which is one 315MHz pair and another one 433MHz pair. The problem the communication become invalid data received.

After do some troubleshooting, i found that if i only use 1 pair RF module and another way use jumper, the system work well again.... from there, i start suspect is interference problem again since, when two pair RF modules are not used together, system will work well.

But one thing i not sure is, why i already use two different frequencies modules, interference problem still occur? Or this may other problem? Can anyone give me advice and solution, thanks thanks.
 
Those data links use very primitive receivers (Superregenerative) that are broad as a barn door. They are not spec'ed for (nor where ever intended to be used for) full-duplex operation. Do you have to use full-duplex?
 
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I think the best way is to go half duplex.. You still have two way communication but only one transmitter running at a time.. There is no way of knowing if the harmonics of the 433 is messing with the 315... You can also buy a pair of transievers ( probably cheaper ). I use Xbee and seem to have very good results in full duplex.

Cheers Ian
 
I agree, the filtering on these tx/ rx are dreadful. Probably drifting all over the spectrum too :)
I suspect that they would probably work as expected if seperated by a little distance. However I reckon that the problem you are experiencing is either one of latency causing framing errors at the uarts, assuming of course that you are not trying to send data faster than the RF modules can cope with, or poor logic levels, so double check the max baud rate that the modules can cope with and back down a step to give yourself a little headroom.

You would be much better using an RF module designed for Duplex comms, something like these would do:
**broken link removed**

rgds
 
You also shouldn't use the USART, you should use Manchester coding (or similar) instead, standard USART data isn't suitable for a radio link - you can also buy radio modules than have Manchester onboard, so those can use standard serial.
 
Hi, everyone...

now i even use 4 different PIC to make communicate, that mean 1 pair PIC for 315MHz and another pair PIC for 433MHz (RF MODULE)
they are already 100% independent, but when both RF modules ON together....interference still happen....

that mean even their frequency band have a 100Mhz++ gap....but why it still affect each other?

May i know the details reason?.... very very very down :-(
 
Hi, everyone...

now i even use 4 different PIC to make communicate, that mean 1 pair PIC for 315MHz and another pair PIC for 433MHz (RF MODULE)
they are already 100% independent, but when both RF modules ON together....interference still happen....

that mean even their frequency band have a 100Mhz++ gap....but why it still affect each other?

May i know the details reason?.... very very very down :-(

It's already been explained in post #2.

And as he also asked, do you REALYY have to use full duplex? - and if so, why?.
 
Hi,

I'm sorry, maybe just my own self dun understand.
I'm now not use full duplex already. The reason why i need to use before is because i need to send control signal to control my car and the data at the car side need to send back to my side and display. so i need both ways communication. so i used hardware usart to do this since the datasheet say it support.

Hmmm, Nigel, May i know even let say it is not intended used in full duplex communication. But just when a 315Mhz and 433Mhz RF module are turn on together, but they are control different devices...but don't they affect each others? Just like in my case, now they are independence at all... no full duplex but juz MCU1 communicate with MCU2 using 315MHz pairs and MCU3 communicate with MCU4 using 433MHz pairs.

Hmmm...i'm sorry, i juz trying to describe my situation...i really wonder why they affect to each other since they are independence.

Thanks.
 
Hi,

I'm sorry, maybe just my own self dun understand.
I'm now not use full duplex already. The reason why i need to use before is because i need to send control signal to control my car and the data at the car side need to send back to my side and display. so i need both ways communication. so i used hardware usart to do this since the datasheet say it support.

Hmmm, Nigel, May i know even let say it is not intended used in full duplex communication. But just when a 315Mhz and 433Mhz RF module are turn on together, but they are control different devices...but don't they affect each others? Just like in my case, now they are independence at all... no full duplex but juz MCU1 communicate with MCU2 using 315MHz pairs and MCU3 communicate with MCU4 using 433MHz pairs.

Hmmm...i'm sorry, i juz trying to describe my situation...i really wonder why they affect to each other since they are independence.

Like I've already said, it was explained in post #2 - crappy receivers.

If you've got BOTH transmitters turned on at the same time, then you're still effectively doing full duplex - you need to turn the unused transmitter OFF, and only ever have one on at a time.

It's really a waste of time having two seperate frequencies, just do half-duplex and turn off the transmitter entirely when it's not sending data. There are transceivers designed to do exactly that, rather than seperate receiver/transmitter modules.
 
Help

Please tell me how did you resolved the problem? I have the same problem.I have buyed already receivers and emitters on 868 and 433 MHz and i don't wan't to buy tranceivers... if you have a solution please tell me. Thank you
 
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