HC-12 Distance Problems

About: retired from electronics and now enjoy inspiring others.

Have poor distance transmission of less than 100 feet or

Just want to know what is a HC-12...GT-38....Read ON.

Hi oldmaninSC about HC-12. I believe this is the BEST transmitter for small data at LONG distances (1/2 mile). Very easy to code and only 4 wires to hook up! BUT there is a major problem. The market is flooded with a BAD version of this module and I would like to clear things up. I must have missed the boat on these because I struggled with complicated NRF, bluetooth, RM28, Xd-fr50, Xbee. All with short range that wouldn't penetrate walls. So all my outdoor TX projects had to be against the outside wall and RX indoor near the same wall. A driveway monitor or yard alarm was way too far to transmit for any of these. Then I saw the HC-12 and saw the 1000 meter range! I got 6 and loaded the code and got great transmissions on my bench but no further than the room and NO penetration of a wall !!! So I ordered more thinking these were defective. Same problem with 8 others all from different sellers. Began to think I was doing something wrong. After a solid week of searching I found a youtube video with the same problem. They tried to test several HC-12 and were using a bike to see how far they could go. They never got on the bike...just a few steps away from the transmitters.... ALL the receivers stopped.

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Step 1: BAD and GOOD

So the problem is the HC-12 WITHOUT the logo www.hc01.com silk screened on the back are BAD. See the photos. Here is another problem.....When I ordered more HC-12 and looked at the photo description and saw the correct module I still got the WRONG HC. Product not the same as shown! Now I wonder if the HC-12 is a hoax and ALL the internet posts are fake.

My last order came in yesterday with the HC-12 logo on the back and I rushed to fire them up and WOW. They really work as stated. I had to walk 3/4 of a mile before they gave out and even then I could turn a certain direction and still pick up the signal . move over NFRs I have some easy code here to download. I mainly use the HC for simple data like time, temperature, alarm, on/off, motion. So I use the transmission of bytes instead of strings. Only so I don't have to turn the strings back into bytes. The library #include SerialSoftware.h has a built in 64 byte buffer so you can send and receive up to 64 bytes of data without collisions. Here is a great HC post. Notice the date. The older HC12 has version v1.6 NOT v2.4 https://www.instructables.com/id/Long-Range-18km-...

photo of front has good on the left and bad on the right

Step 2: Basic Codes for Bytes

The GOOD news..BAD news.

I have connected the good and bad HC to an millamp meter and watched the power. The good HC pulls about 100ma in transmission at power 8. and pulls about 2ma in power 1. The bad always pulls 2ma in any power level. If you read the datasheet for the si4463 the default mode for transmission is LOW (power 1). I have checked foil runs, components, and any changes from the good and bad and can't find anything different. Then I saw a post for bad HC with NO AT commands. Now I believe the problem is that the firmware is bad. In the factory, the test would be on the bench....so who would test a module outside 1000 meters? I think the wrong TX register is being used. The GOOD news is that all those bad HC can be used as receivers. I restored all my bad HC with AT+DEFAULT and tested them for distance. They ALL went 3/4 of a mile in the RX mode. I did see a post where an older version and a newer version did not work well and only got about 100 meters. But none of mine did. The other GOOD news is the bad HC-12 now has a bad name and the replacement is GT-38. This looks the same but it works!

Step 3: Conclusion and Hopeful Help

Cheep knock off products WILL ALWAYS be around. Twenty some years ago the news program 60 minutes showed Microsoft cds being copied at night in the same factory that was granted the copy right contract.! Just a few years ago Arduino FTDI chips were copied and when you loaded the drivers, windows detected the fake and erased it. Just wished someone told us. As I spent months trying to fix the problem. I wish INSTRUCTABLES would keep this post alive so we can keep from pulling our hair out.

My last comment is for the really SMART computer people. I tried to find the firmware V2.4 for the HC-12. I could NOT. I hope someone reads this and shows us in STEP by STEP how to download a correct version of the firmware if this IS THE problem. Just having the firmware is ok but I haven't a clue how to download it into the two gold pins on the back of the HC-12. But now that I have good HC-12 I can just consider the bad ones as learning mistakes.

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    6 Discussions


    14 days ago

    Thank u for post. I was near to brake my head). I also bay 2 modules and they work fine. After some time i bought new 5 psc and they have connection only at several meters. And this is NOT due to wrang firmware, because I use my own firmware. I use this modules without extermal mcu, and use it as remote contact on one and button on another with feedback. So for this aim enough available 3 external pins (tx, rx and set).
    Good modules work fine with my own firmware, bad ones have mentioned issues.


    18 days ago

    @oldmaninSC Thank you so much for this post. Your findings reflect exactly what I have been seeing but could not explain. Luckily for me the first batch of HC-12 I bought were GOOD so I got the prototypes up and running and working at a good range. I then started producing the 20 receivers and 6 transmitters of my project and ordered a second batch from the same supplier. Well turns out second batch is the BAD ones! Could not understand why 2 of the transmitters worked up to 3/4km and the others would not.

    Gad to hear that as a receiver they all work just as well, means I do not have to rip apart the last 10 boxes I have just built.

    2 replies

    Reply 14 days ago

    Yes, I tore my hair out for over a month thinking it WAS ME. I tried to get the GOOD hc12 with the larger micro marked 8s003 but the GOOD hc12 has the smaller micro. The whole reason is that I wanted to SWAP the micros from good to bad and see if that fixed the problem. And the GT-38 that looks just like the HC12 works well but NOT with the HC12


    Reply 14 days ago

    I managed to get 10 more good ones from eBay the other day by looking for the ones with the two small ICs not the bigger ones. Using my SDR I can see the power output of these ones are -8db rather than -21db. Now I have to rip apart 2 transmittors and add the new cards :(


    6 weeks ago

    I have a farm with a water tank on a hill about 1 Km line of sight . I have used TX01 and RX9 modules from Oatley for about 4 years now. They are cheap but run on 12 Volt. I think they are on EBay too. You can also use PVJ6WC module too. They are not bad at going through concrete walls either at this lower frequency . The lower the frequency the further the wave will travel of course.


    1 reply

    Reply 6 weeks ago

    thanks for the info. But the GOOD hc-12 is just too easy to work with. My post intention was to help anyone who had a BAD hc-12 they couldn't get to work and thought it was something they were doing wrong .