Comparison of RF modules

[faryal]

I need to ask that if low cost RF module is available like (433 MHZ xy-mk-5v) and it can be used for automation projects( like controlling room appliances) then why people use other expensive RF modules like HC11 and zigbee etc in the same projects? please let me clear about this very basic confusion as I need to use it in my project.

 

[WimRFP]

Re: comparasion of RF modules

It is all about what the user expects and what happens when the wireless link fails.

If a user wants to control a crane via wireless remote control, you don't want that a nearby broadcast transmitter interferes with the remote control. Though there are safety provisions in case of failure of the link, you want to keep the down time to a minimum. In case of a simple (cheap) remote controlled toy (slow speed), you can accept failure due to (for example) interference.

Nowadays there are minimum performance criteria for remote controls in at least in the EU and other countries that adopt ETSI standards. These specify adjacent channel and adjacent band selectivity, blocking/desentizitation, etc. You may search for low power device receiver class ETSI and check the regulatory information of for example Nordic and TI.

The more one is dependent on the operation of a remote control, the higher the requirements.

 

[faryal]

Re: comparasion of RF modules

So u mean to say that expensive RF modules don't face interference like things? But what is the reason behind it?

 

[WimRFP]

Re: comparasion of RF modules

We have to share radio spectrum with many people. Very cheap RF modules can be overloaded easily by emissions in adjacent bands. I am not up to date with the newest modules, but I have met really bad modules (bad sensititivy and very poor out of band receiver performance). You may also know that in several countries 433 MHz is inside the 70 cm radio amateur band.

Up to 430 MHz you may encounter trunking two-way radio systems (for example TETRA). Around 446 MHz you have PMR, above 450 MHz you may encounter two-way radio communication (including trunking networks) and cellular radio.

Good modules have descent RF circuitry to receive only the frequency you are transmitting, reducing the change on interference from out of band emissions. Don't forget that the 433 MHz band is used by others also, so your system should be able to handle in-band interference (you can't avoid, even with the most expensive module).

Did you also consider 868 MHz? If so note that in many countries 850 MHz is used (or planned) for LTE. Poor quality 868 LPD modules may experience interference from 850 MHz LTE and other services.

You should ask yourself the question: what if the communication fails (user acceptance, risk on injury, other altenatives, just annoying, etc)? If is it really important that the communication does function, you need to use good modules.

 

[stillcrazy]

Re: comparasion of RF modules

Have a look at www.dorji.com. They have quite a range of wireless modules.

 

[faryal]

Re: comparasion of RF modules

I have got to use XY-MK-5V TX/RX Module in my project of "room automation system". I am using pic microcontroller and C language. I need to ask that will this RF module will on/off a 220V bulb and fan?? will it need encoder/decoder or just pic uC will be sufficient??

 

[bigdogguru]

Re: comparasion of RF modules

Besides the important issues mentioned by WimRFP, the less expensive TX/RX modules, like the common 433 MHz ASK modules, lack any implementation of an encoding/decoding scheme.

Encoding/decoding schemes are particularly important concerning the transmission and reception of data, therefore typically either external encoding hardware, like the HT-12E/D devices, or a software implementation of an encoding scheme must be employed.

The more sophisticated RF modules incorporate the required encoding hardware into their designs.


BigDog

 

[faryal]

433MHz or 2.4GHz suitable for a room automation system project?

I have to make a room automation system for disabled person. I need to ask whether 433MHz RF module is sufficient for this purpose or I need to use 2.4GHz RF module beacuse I have heard that 433MHz is most suitable for small on time purposes like garage door openers etc... As 433MHz is less expensive as compared to 2.4GHz so I'm preffering 433MHz but what is your opinion, will it fulfil my required project?

 

[betwixt]

Re: 433MHz or 2.4GHz suitable for a room automation system project?

Both have a range far wider than a room. Possibly 433MHz will travel better through walls but it depends on the building construction. The only real difference you might see is that 433MHz is a crowded frequency, being used for many purposes, so you might suffer from interference there, especially if you are in a highly populated area. Both frequencies can be and are used for short range data communication so from a functional aspect it makes little difference which you pick.

Brian.

 

[faryal]

RF module + uC + encoder/decoder usng DTMF

I have to control multiple devices by transmitting RF signal through RF module(433MHz), it is interfaced with microcontroller, but there is a confusion why there is a need to use encoder at tx side and decoder at rx side when uC can done this function. Actually encoder is DTMF (tp5089 ic), it generates a signal in tone form and that tone is received by the RF receiver and then decoder again decode that dtmf tone in ttl logic form. but why?? I'm confused why the signal is transmitted in tone form, why dtfm encoder is used here? why the signal does not go directly from uC to RF transmitter? please explain and clear my confusion....:sad::-|

 

[WimRFP]

I assume that failing of the system reduces quality of life for the disabled person. So mailfunction of the system is not just an annoyance. If this system is for series production, it is good to inform yourself about performance criteria for SRD devices (if applicable for sales region). It becomes even more complicated as it is assumed a medical aid.

When we combine the answers from Bigdogguru, Betwixt and myself:

-Use a good module (read compliance and performance info from major suppliers so that you know what you need)
-Your software (both the application and low level communication) should be able to handle interference in the communication (retransmission, error correction coding, fail safe modes, etc).
-Use a frequency that is not very crowded, overhere 868 MHz is better regulated (and is not an amateur band where you may expect transmission with >100W power).
-try to figure out what other people did for similar applications. My preference (living in EU/NL) is a suitable part of 868 MHz band (that is not that part of the band where there are 2W RFID systems).

 

[FvM]

Re: RF module + uC + encoder/decoder usng DTMF

I wonder which RF module is prepared to transmit an analog baseband signal as the DTMF generator output? Likewise standard receiver modules have digital outputs not suitable to feed a DTMF decoder.

In so far the sketched solution seems to be unusual and probably depends on specific module hardware. More often RC encoder/decoder chips are used with simple RF modules, particularly from those designers who don't manage to software encode the data for reliable transmission with RF modules.

The required characteristics of a software encoder and decoder have been quite often discussed at edaboard.

 

[bigdogguru]

Re: 433MHz or 2.4GHz suitable for a room automation system project?

As 433MHz is less expensive as compared to 2.4GHz so I'm preffering 433MHz but what is your opinion, will it fulfil my required project?

There are several quite inexpensive 2.4GHz options available, if the design utilizes a microcontroller at both endpoints you might consider employing a pair the Nordic nRF24L01+ modules which utilize the common SPI interface. Pairs of nRF24L01+ modules can be readily purchased for under $3 USD for the pair.

They have several advantages over ASK/OOK TX/RX modules as they are bidirectional transceivers, embedded encoding/error correction, up to 2Mbps throughput, numerous open source libraries for many common microcontroller families, ultra low power modes, etc.

Nordic Semiconductor nRF24L01+

eBay Search - nRF24L01+


BigDog

 

[faryal]

thanks for guiding but un fortunately I have purchased ASK RF module 433MHz (xy-mk-5v) and I have a serious question regarding it I have to control multiple devices by transmitting RF signal through RF module(433MHz), it is interfaced with microcontroller, but there is a confusion why there is a need to use encoder at tx side and decoder at rx side when uC can done this function. Actually encoder is DTMF (tp5089 ic), it generates a signal in tone form and that tone is received by the RF receiver and then decoder again decode that dtmf tone in ttl logic form. but why?? I'm confused why the signal is transmitted in tone form, why dtfm encoder is used here? why the signal does not go directly from uC to RF transmitter? please explain and clear my confusion....

 

[betwixt]

Sending as audio isn't fast but it is simple. You can simply send as digital data but there are drawbacks for which you have to actively defend. Primarily, the receiver will tend to produce random output when it has no input signal. This is analogous to background hiss when a radio receiver is 'off tune' but being a random logic level instead, it can be misinterpreted as real data. You have to build protection into the data stream to be a certain as possible that it comes from the right source and isn't corrupted. Sadly it's much more complicated than just wiring data in at one end and taking it out at the other.

Brian.

 

[FvM]

Actually encoder is DTMF (tp5089 ic), it generates a signal in tone form and that tone is received by the RF receiver and then decoder again decode that dtmf tone in ttl logic form. but why??

What does this mean? Do you have a working prototype using an ASK transmitter and receiver together with DTMF encoding, are you referring to an existing schematic or is it just an idea?

I already answered the other question in your repeated post.

Yes, you can operate ASK RF modules directly with microcontrollers on the TX and RX side. But you can't reliably transmit a binary UART signal without special encoding. Some module vendors have published software libaries for Arduino that can be adapted for other processors.