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what frequencies can one use on the feather lora m0 433 mhz
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what frequencies can one use on the feather lora m0 433 mhz

by gersart on Thu Aug 15, 2019 3:31 pm

I have an installed system with 12 suitcases communicating. Each has an Adafruit Lora 433 Mhz m0 feather in it.

Currently the suitcases only send a start/confirm command between each other.

This is currently installed on a busy campus, in a building which uses some wireless devices, such as specialized remotes or wireless headset microphones.

The software is all set to communicate at 434 Mhz, the default for the code from Radiohead, which is recommended for these feathers.

Occasionally the communication between suitcases will stop, and if I reset one then it will resume. I have places in the code where this is supposed to happen automatically but that isn't working as planned when unsupervised (if it receives no confirmation it should resend the code in two minutes)

Is it possible that some other device is interfering with this communications system, and can I use a lower frequency than the one I am using (ie will 330Mhz work even though the lora is set for 433?) The code implies that the frequency can be set, but I have not found any information as to the range one can set it to for dependability...

I appreciate any help with this.

gersart
 
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Re: what frequencies can one use on the feather lora m0 433

by gersart on Thu Aug 15, 2019 4:43 pm

I have confirmed the building has a block of frequencies between 470Mhz and 510Mhz for their microphones.

This shouldn't be a problem.

Could setting the feathers to 350 Mhz or so be a solution? I cannot tell if the lower frequencies can be used or only the highest frequency on the devices..

Any help would be appreciated.

gersart
 
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Re: what frequencies can one use on the feather lora m0 433

by adafruit_support_mike on Sat Aug 17, 2019 12:49 am

The radios themselves can tune a wide range of frequencies, but the radio modules have built-in antennas that select specific frequency ranges.

That's a fundamental part of the radio modulation/demodulation process. The receiver hears signals at all frequencies, but all the signals outside the band of interest create noise that blocks out the signal the radio wants to hear. Passing the raw signal through a filter gets rid of signals at frequencies significantly higher or lower than the band of interest, allowing the radio to hear the signals it wants more clearly.

If you tune the radio to a frequency outside its filter band, it's like trying to shout through a pillow. Eventually, the filter will block most of the signal you're trying to send or receive.

You also have to be careful about staying inside the legal frequency bands. The FCC's spectrum allocation table has lots of bands assigned to specific purposes, and you have to be licensed to operate radio equipment in most of those bands. The 433MHz and 915MHz bands are reserved for unlicensed transmission.

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Re: what frequencies can one use on the feather lora m0 433

by gersart on Sat Aug 17, 2019 12:33 pm

Thank you.

I am building a kickstart listener out of a spare feather to send a start command if it hears nothing for more than a minute.

I also realized that these suitcases have been running for almost two weeks, only being reset if I did so to fix a problem. There is a chance my code has an overflow error of some kind.

If I reset all devices daily AND install the kickstart listener, the system may be more stable.

I will have to find the reason for this eventually, though. They are too unstable for a dependable install if they were in a gallery I wasn't near.

gersart
 
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Re: what frequencies can one use on the feather lora m0 433

by adafruit_support_mike on Sat Aug 17, 2019 11:17 pm

Keep collecting information. The more you know about a system's conditions when it does fail, the better you're able to find a solution.

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Re: what frequencies can one use on the feather lora m0 433

by gersart on Tue Aug 20, 2019 6:38 pm

Thank you very much for your answer.

I tried resetting the machines daily to see if there was a software problem and the miscommunication seems to have been avoided.
I suspect there is a memory leak in my code. I now reset the suitcase feathers when plugging them in at night and first thing in the morning without any mishaps during the day.

Previously they were giving problems after the third or fourth day.

If I could add a way to have them do a software reset somehow I would add that to the system with a counter. After two hours they would reset themselves.

I have not been able to find any solution for resetting in software except for one on Arduino Zeros:

Code: Select all | TOGGLE FULL SIZE
NVIC_SystemReset();      // processor software reset


https://forum.arduino.cc/index.php?topic=379950.0

Since this is an Arduino Feather M0 LoRa, I am unsure if it will have the same effect.

gersart
 
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Re: what frequencies can one use on the feather lora m0 433

by adafruit_support_mike on Wed Aug 21, 2019 12:06 am

Yeah, that command works on all M0 boards.

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Re: what frequencies can one use on the feather lora m0 433

by gersart on Thu Aug 22, 2019 11:48 am

thank you.

I shall try to integrate that within the current scheme.

Still trying to figure out how to determine if there are no communications found over a period of 60 seconds.

gersart
 
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Re: what frequencies can one use on the feather lora m0 433

by adafruit_support_mike on Fri Aug 23, 2019 1:05 am

Every board should be able to track the time of its last transmitted or received message. The millis() function isn't great over the long term, but is okay for measuring periods of 'about a minute'.

If you have a transmitter that wants to know if the receiver got the message, you can use a call-and-response strategy: the sender tacks a random number onto the end of each message it sends. The receiver reads its input, then sends the random number back to the sender. If the sender gets the right value in the reply, it can be reasonably sure the message went through correctly.

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