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RF data transfer questions.
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Dubbie:
Hi all,

I need to make a small receiver type device that needs to be as cheap as possible and have a receive range of about 50m. I only need to send about a dozen bytes or so, and there are no unusual constraints around speed or timing. Frequency would be 433Mhz

I was planning to use an all in one Micrel IC to handle the radio reception and transmission and a small mcu to do something with the data.

Where I am a bit confused is with the best way to actually send the data. I will probably use FSK modulation, but what exactly do I feed into this? I haven’t been able to determine what is usually done in this situation for data encoding. There are tons of higher level protocols it seems like zigbee etc. but none that I came across for bare basic communication. Do I need to write some scheme from scratch using Manchester encoding (which I am willing to do if necessary) or is there something that people far smarter than me have already invented? Or do I just simply plug UART TX into my radio?

Thanks for any advice.
pwlps:
You can check RF-modem modules like

https://www.rfsolutions.co.uk/radio-modules-c10/fm-zeta-transceiver-module-optimised-for-433mhz-p405
https://www.rfsolutions.co.uk/radio-modules-c10/alpha-trx-low-cost-high-performance-transceiver-module-p383

They work like modems i.e. they handle all the modulation/coding stuff, you just see a serial (SPI) IO.
schratterulrich:
Once I successfully implemented a radio remote control in which I simply used the UART TX. I had no problem with the DC content of the signal with my Transmitter.
 
First transmit a few bytes 0101010... So the receiver can level its AGC and comparator for creating the logic levels from demodulator circuit to a correct level.
Then simply transfer the payload data and then at least 4 bytes checksum. (some kind of CRC or similar, keyword Hamming distance)

A trap can be that the receiver always receives data (noise) even if the transmitter is not transmitting at the moment. This means if we use a baudrate of 9600 than the 4 checksum bytes are received 300 times per second. With 32 Bits checksum the possibility is 1/4.294.967.296 that the checksum is coincidentally correct. This means further this happens once every 165 days. Maybe you should better use even more checksum bytes…
Dubbie:

--- Quote from: pwlps on June 19, 2019, 07:51:06 am ---You can check RF-modem modules like

https://www.rfsolutions.co.uk/radio-modules-c10/fm-zeta-transceiver-module-optimised-for-433mhz-p405
https://www.rfsolutions.co.uk/radio-modules-c10/alpha-trx-low-cost-high-performance-transceiver-module-p383

They work like modems i.e. they handle all the modulation/coding stuff, you just see a serial (SPI) IO.

--- End quote ---

I was hoping to achieve significantly lower cost than those all in one type solutions.

my current thinking is to use this part:
https://www.silabs.com/documents/public/data-sheets/Si4356.pdf

it's cheap and supports the power range I am planning on using.

With that and a microcontroller, I am only at less than $2.50 in 1 of quantities.
Dubbie:

--- Quote from: schratterulrich on June 19, 2019, 07:58:17 am ---Once I successfully implemented a radio remote control in which I simply used the UART TX. I had no problem with the DC content of the signal with my Transmitter.
 
First transmit a few bytes 0101010... So the receiver can level its AGC and comparator for creating the logic levels from demodulator circuit to a correct level.
Then simply transfer the payload data and then at least 4 bytes checksum. (some kind of CRC or similar, keyword Hamming distance)

A trap can be that the receiver always receives data (noise) even if the transmitter is not transmitting at the moment. This means if we use a baudrate of 9600 than the 4 checksum bytes are received 300 times per second. With 32 Bits checksum the possibility is 1/4.294.967.296 that the checksum is coincidentally correct. This means further this happens once every 165 days. Maybe you should better use even more checksum bytes…

--- End quote ---

thanks for the advice.

I hadn't ever really considered the innevibility of an accidental checksum reception!
I'll keep that in mind.

R
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