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I think I have a bad batch of HC-12 radio modules. (FIXED)

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camerart

Well-Known Member
Hi,
I use the HC-12 radio modules for send/receive data. These are very good for this type of thing,

The latest batch of modules, from 'can't remember' don't transmit properly.
Normally I can READ the output on a computer terminal, but also listen for the signal using a hand held radio, for checking.
This batch send an audible signal, but it isn't as 'bright' as the ones that work, so the data doesn't get received by the RX one.
Here's photos of both:
I've seen similar problems in the past, but not with this particular module.
Cheers, Camerart
hc-121.jpg
hc-122.jpg
 
I had a batch of HC12s that did not work with the HC12s that I had bought before. On investigating the problem I found that the new batch all worked with each other. A web search indicated that a manufacturer had built them using out of spec crystals. I did some tests and found that the suspect batch where not quite on the correct frequency. I sent them back and obtained a refund. I ordered them again from a different supplier and they worked correctly.

Les.
 
Your new ones look to exactly match the details for the present HC-12 module on the manufacturers site.
Look at the photos part way down the page.

Some other info implies the channel numbering may be one off between old batches and the later ones? eg. The setting needs to be one channel different.
 
I had a batch of HC12s that did not work with the HC12s that I had bought before. On investigating the problem I found that the new batch all worked with each other. A web search indicated that a manufacturer had built them using out of spec crystals. I did some tests and found that the suspect batch where not quite on the correct frequency. I sent them back and obtained a refund. I ordered them again from a different supplier and they worked correctly.

Les.
Hi L,
I'll try swapping the crystal over.

Do you have a link to the 'correct' manufacturer?
C
 
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I would not advise attempting to swap crystals on HC12s. Just test to see two of the new (Suspect.) batch of HC12s work together. I just connect one to a PC using a USB to serial module. Power the other one up and connect RX and TX together. Run a terminal emulator program on the PC. If the two HC12s are communicating you should see the characters you type displayed on the screen.

Les.
 
I had a batch of HC12s that did not work with the HC12s that I had bought before. On investigating the problem I found that the new batch all worked with each other. A web search indicated that a manufacturer had built them using out of spec crystals. I did some tests and found that the suspect batch where not quite on the correct frequency. I sent them back and obtained a refund. I ordered them again from a different supplier and they worked correctly.

Les.
Hi L,
I swapped the crystals, no difference, so could be capacitors. They still transmitted, with a different sound.
C
 
Hi,
Here are some readouts from an SDR screen.

The not working one is on the correct frequency, but not a big signal.
C
 

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Very interesting...
and totally different.

One thing I notice is that the Not Working module creates about 10dB of wideband noise across the width of your SDR display.
The amplitude of the noise rises at lower frequencies.

You are currently scanning from 433.7 to 433.9 Mhz,
would it be possible to look at lower frequencies to see if there is something significant lower down the band?

Wideband noise from a transmitter usually reduces the further you go from the carrier, so I have this feeling that there may be some signal from your module clattering away lower down the band.

JimB
 
Very interesting...
and totally different.

One thing I notice is that the Not Working module creates about 10dB of wideband noise across the width of your SDR display.
The amplitude of the noise rises at lower frequencies.

You are currently scanning from 433.7 to 433.9 Mhz,
would it be possible to look at lower frequencies to see if there is something significant lower down the band?

Wideband noise from a transmitter usually reduces the further you go from the carrier, so I have this feeling that there may be some signal from your module clattering away lower down the band.

JimB
Hi J,
Judging by my images, I wouldn't treat them too precise, but they do give a good indication of what you suggest.

I got pretty mixed up getting them in order, so hopefully, they are.
C
 

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The Not Working one seems to be all over the place, a real bag of nasty.

JimB
 
Hi,
I've been messing about with my HC-12s some that I broke and the ones above that I called 'bad'

Apart from the ones marked broken, the 'bad' batch don't appear to be programming, so they oare on the next channel to the one I thought.

I tried various frequencies, but they won't change. I hold the 'set' button type AT+00X and get the OK, but they don't change.
Any ideas?
EDIT: Just read the manual again, and find that I didn't add the 'C' when programming. AT+C00X OK+C00X So problem fixed.
C
 
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