Learning about 433 MHz radios - how?

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turboscrew
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Learning about 433 MHz radios - how?

Post by turboscrew » Thu Mar 16, 2017 12:09 am

I'd like to fool around with a couple of blue pills with 433 MHz radio modules, but to make some sense
out of the radio module data sheets, I guess I should learn some radio basics first, but how?

I've been trying to search the net for tutorials or something, but I don't really even know what that sort of
technology is really called. What I think I need is the basic theory and terminology, like 'noise figure' or
'fading margin'.

The point is to learn about the radios, not to get away with it by just downloading a ready-made application
or library. (I did, however, download this: https://github.com/LowPowerLab/RFM69 for reading.)

So does anyone know good links or even googling phrases?

zmemw16
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Re: Learning about 433 MHz radios - how?

Post by zmemw16 » Thu Mar 16, 2017 12:26 am

'arduino 433mhz instructable'
not exactly that difficult :!:

first item

you will probably need to add correct lengths of wire as aerials to improve range, maybe not for 2-3ft( :?: :?: :?: )
after that essentially its connecting arduino uart to tx, rx to another arduino's uart

stephen

turboscrew
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Re: Learning about 433 MHz radios - how?

Post by turboscrew » Thu Mar 16, 2017 10:28 am

zmemw16 wrote:'arduino 433mhz instructable'
not exactly that difficult :!:

first item

you will probably need to add correct lengths of wire as aerials to improve range, maybe not for 2-3ft( :?: :?: :?: )
after that essentially its connecting arduino uart to tx, rx to another arduino's uart

stephen
I came across that page, but I recall it just showed how to wire it up and then used a ready-made code.
The wiring / antenna are not problems, but how to program the rf-chip is.
And my plan is to use a CC1101-based USB-dongle too, so I will need to make the parameters match the
dongle's. (The dongle's parameters can't be changed - except the IDs, tx power and serial port baud rate.)

(Yes, I checked: "Fortunately , There is a popular Library for arduino Called "" VirtualWire"" Created by Mike McCauley".)

As aerials, I have "short whips" and I plan to try 1/4 wave length dipole(s) too.

[edit]
I did download the radiohead library too. Maybe it teaches me something too...
[/edit]
Last edited by turboscrew on Thu Mar 16, 2017 11:08 am, edited 1 time in total.

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zoomx
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Re: Learning about 433 MHz radios - how?

Post by zoomx » Thu Mar 16, 2017 10:38 am

zmemw16 wrote: after that essentially its connecting arduino uart to tx, rx to another arduino's uart
I used these modules with Arduino but with other pins, not the serial pin. The communication between cheap modules and Arduino is not a serial communication.

I believe that the library was Virtual Wire but there is a new one that works with many modules.

turboscrew
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Re: Learning about 433 MHz radios - how?

Post by turboscrew » Thu Mar 16, 2017 11:15 am

I also think that the virtual wire will not be enough.
I'm planning to make a small (maybe 3 - 6 nodes) network.

And usually the processor interface for those cheap modules seems to be SPI.
But for dongles it's UART (USB-UART).

turboscrew
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Re: Learning about 433 MHz radios - how?

Post by turboscrew » Thu Mar 16, 2017 1:51 pm

BTW, does anyone know why the limitation (RFM69)? (What does this mean?)
FDA + BRF/2 =< 500kHz

FDA = frequency deviation, FSK
BRF = bit rate, FSK
And BRF max = 300kbps.

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zoomx
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Re: Learning about 433 MHz radios - how?

Post by zoomx » Thu Mar 16, 2017 2:12 pm

I am not sure but it seems that these cheap modules (less than 2$) work with OOK modulation, so the pin turn on and off the carrier. They are very simple modules.

There are some other modules that works better.

If you need a network maybe you can consider NRF24 based modules.

turboscrew
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Re: Learning about 433 MHz radios - how?

Post by turboscrew » Thu Mar 16, 2017 5:35 pm

RFM69 knows FSK and GFSK too (€ 3,17 / piece). And it has 66-byte FIFO.
"FSK, GFSK, MSK, GMSK and OOK modulations"
"Packet engine with CRC-16, AES-128, 66-byte FIFO Built-in temperature sensor"
http://www.hoperf.com/rf_transceiver/mo ... M69HW.html

I also ordered CC1101-based modules, but they have not arrived yet ( € 3,32 / piece, US $3.50 / piece).
"The maximum rate of 500kbps, support 2-FSK, GFSK and MSK modulation."
"Built-in hardware CRC error detection, and address control"
"Separate 64-byte RX and TX data FIFO "
https://www.aliexpress.com/item/2-pcs-C ... 0.0.dXdbgJ

And this is the dongle I mentioned earlier. (Not very good idea - it can't be used for sending binary data.)
https://www.aliexpress.com/item/433Mhz- ... 42842.html

Not quite that simple even if cheap.
Oh, and both modules use SPI as the processor interface.

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RogerClark
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Re: Learning about 433 MHz radios - how?

Post by RogerClark » Thu Mar 16, 2017 9:06 pm

nRF905 is another option

but I had to hack an AVR library to use it, and the result was not pretty;-)

I like nRf905 as it us multi-band, not just 433MHz, but I think it can only transfer 32 bytes at a time, as its intended to communicate with other nRF905 devices using its own protocol.

Ps. They are less than $5 on aliexpress.

turboscrew
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Re: Learning about 433 MHz radios - how?

Post by turboscrew » Fri Mar 17, 2017 8:51 pm

I already have 4 RFM96s, and two CC1101s are on their way...
I guess RFM96 is enough for now even if, with the on-chip AES, the message can be only 48 bytes
(if address filtering is used - and I intend to use it at some point).
It can also deal with unlimited length messages, but some features are not available then.

Anyway, I seem to be learning a bit by reading the manual over and over, but I guess I'd still
benefit from some theory/practical info.

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