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Forum Index : Microcontroller and PC projects : HC-12 old vs new module....
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Azure Guru  Joined: 09/11/2017 Location: AustraliaPosts: 446 |
Yes and No, it depends on the application for most general use that would be a fair statement. From my memory using different Tx/Rx Freq crystals was for one way communication. The crystals were matched (or mismatched depending on how you look at it) by the IF frequency. Each Crystal was still marked with the crystals actual frequency, just they used a different frequency in the Tx unit and the Rx unit. This meant for the remote controls back then you had to have a Tx/Rx pair for every channel you were going to use in your remote. Hopefully the Rx unit was easy to access to swap the Rx Crystal, sometimes they were tucked away for replica or small scale models. |
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| PeterB Guru Joined: 05/02/2015 Location: AustraliaPosts: 643 |
My experience with radio control was very limited but I seem to remember Xtals could be marked e.g. T27.xxx for Tx and R27.xxx for Rx and the two frequencies, although marked the same, were different by the IF. I think there was also a letter code. My experience was in two RC tanks for a nephew who was only 50 at the time. Peter |
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| Boppa Guru Joined: 08/11/2016 Location: AustraliaPosts: 814 |
Correct PeterB, also used was a grey heatsrink for rx and a black one for tx The marking was 'usually' for the nominal frequency, the actual frequency the crystal ran at could be a number of different actual frequencies, depending on use, it could be at the actual frequency, it could be (from memory here, so actual numbers may be wrong) 455khz out, 10.7or 10.8??mhz out, or it might be used at a multiple so if using 2nd harmonic could be half the cases written frequency There were also different 'cuts' which had an effect as well, but that I am hazy on (was a long time ago I regurly played with them, back in the old 18/23 channel cb's and 3 channel dse/tandy walkie talkies, then remote controled planes for a while) One trick we used to do to get 'private' channels on crystal controlled two ways was swap the rx and tx crystals on one channel, that way standard sets couldnt pick up our tx's (good for fox hunts lol)- also worked when you were in congested airways in the city (are you PeterB from SSSF by any chance? |
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| PeterB Guru Joined: 05/02/2015 Location: AustraliaPosts: 643 |
I have often wondered if it was possible to swap Xtals and hence move the channel by twice the IF. I am not PeterB from SSSF, well I don't think so. What is SSSF? Peter oops. Move the channel by the IF. I hope that's correct. Peter |
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| Boppa Guru Joined: 08/11/2016 Location: AustraliaPosts: 814 |
Was an old forum now closed that had a PeterB as well (was run by the ABC for Dr Karl) |
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Grogster Admin Group  Joined: 31/12/2012 Location: New ZealandPosts: 9082 |
UPDATE: Phil over at the PICAXE forums has received two of my clone modules, and has tested the crystals - they are stunningly bad...... An extract from an email that he sent me: [Quote=Phil from PICAXE forums]28.5MHz and less than half the amplitude of the signal across the “T300” crystal![/Quote] Please visit the PICAXE thread for an image he has posted comparing the genuine with the clone crystals. I have asked him in an email if I can repost his image here, because you can't get the full-size image from the PICAXE forums, unless you are logged in, and many members here won't be members of the PICAXE forums. As soon as he says that is OK, I will re-post his image here. EDIT: Permission granted from Phil to re-post his scope image, so here you are:  For a crystal that is supposed to be 30.000MHz, this is not good....  Smoke makes things work. When the smoke gets out, it stops! |
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| Grogster Admin Group Joined: 31/12/2012 Location: New ZealandPosts: 9082 |
Just a little update for this thread: [Quote=reginald on the PICAXE forums]I had three HC-12 30mhz crystal variant left whch did not communicate well(or at all) over distance with my T300 type. I obtained new crystals from farnell type 7M-30.000MEEQ-T - Crystal, 30 MHz, SMD, 3.2mm x 2.5mm, 10 ppm, 10 pF, 10 ppm, 7M Series stock No 2308724 Swapped these today and now all three boards are happy chatting away with no errors. One was a USB type plugin which failed and on opening up it had a HC-12 board piggy backed on the USB board which I had swapped with 30mhz type (before I new the difference) and wondered why it didin't work. Shows not all crystals are equal.[/Quote] I have ordered some new crystals, but they are not here yet. I got mine from Element-14 here. I am now very hopeful that I can revive some of my dead ones by recrystallizing them. Smoke makes things work. When the smoke gets out, it stops! |
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CaptainBoing Guru Joined: 07/09/2016 Location: United KingdomPosts: 1995 |
good stuff! keep us in the loop |
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| paceman Guru Joined: 07/10/2011 Location: AustraliaPosts: 1329 |
Grogs, you're famous - this HC-12/crystal problem thread made "Hackaday" - here Greg |
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| CaptainBoing Guru Joined: 07/09/2016 Location: United KingdomPosts: 1995 |
... which completely justifies the in-depth detective work undertaken by the entire thread. Just look at the coverage and potential pain you have saved others. good stuff! |
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| JohnS Guru Joined: 18/11/2011 Location: United KingdomPosts: 3678 |
Congrats to Grogster! John |
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| Grogster Admin Group Joined: 31/12/2012 Location: New ZealandPosts: 9082 |
@ paceman - thanks very much for the link! Crikey!  Nice to see most of the comments support what we have found out thus far. Usually, the comments section on blogs can get nasty if people still think you are wrong. For the record, I am perfectly prepared to accept anyone else's point of view, and if they can demonstrate that the testing done thus far was fundamentally wrong, I will listen.  There. That should keep everyone happy.  My replacement TXC-genuine crystals have arrived, and when I get a spare moment, I plan to replace the crystal on one module with the TXC one, and see if I can replicate the results from reg on the PICAXE forum thread. I am quite hopeful that I will. (fingers crossed) Smoke makes things work. When the smoke gets out, it stops! |
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| Grogster Admin Group Joined: 31/12/2012 Location: New ZealandPosts: 9082 |
OK, after about half an hour, I have replaced one 30.000MHz crystal, with a genuine 30MHz one, and just like reg on the PICAXE forums, this module now works spot-on frequency as it should be. Replacing the tiny crystal package was a pain in the arse. Reg made it sound so simple....  I will practise on another module tomorrow. I think part of the problem is my rework station has a very small nozzle on it - 2.5mm OD, and 1.8mm ID, which is pretty small, and I think it just is not heating up the crystal package evenly enough, cos even if you 'Draw circles' around the package, one side is cooler then the other, and starts to re-solidify and then the bloody thing won't shift.Even with my rework station up at full-temperature, and air on 2.5 of 8, it took ages to get the old one to move, and ages to get the new one to reflow. Perhaps I am doing something wrong there with my technique. My rework station is a Hako 851 if anyone is interested. It would be quite old now I think. Perhaps it is time I got another one along the lines of something like this. Smoke makes things work. When the smoke gets out, it stops! |
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| CaptainBoing Guru Joined: 07/09/2016 Location: United KingdomPosts: 1995 |
well done grogs - you are the HC-12 master!!!  I had one of those heat guns... packed up after an hour and got a refund. The magic smoke came out - really! Went for one of these (same item, different seller) instead and it has done sterling work with no hassle seen on the benches of a few leccy nerds I follow on YT also |
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| Grogster Admin Group Joined: 31/12/2012 Location: New ZealandPosts: 9082 |
Yes, I have seen those ones around on videos etc often, so they are obviously quite popular. I have ordered one of the ones I linked to. I like that one, as it comes with 9 nozzle types including a QFP one. With this, I am hopeful for better results then with the Hako one with the tiny nozzle, because I can choose a nozzle that is bigger and get more even heating for crystal removal/replacement. Smoke makes things work. When the smoke gets out, it stops! |
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Turbo46 Guru Joined: 24/12/2017 Location: AustraliaPosts: 1595 |
Well done Grogster! Just when I was going to buy some to play with. All I need to know now is - where to buy genuine HC-12s from? Am I best to always buy them from the one supplier so they all should at least be compatible with each other. Looking at the many hits I get on the web only the ones on the HC01.com site look genuine that I can tell but I don't know how to purchase from them. Bill Keep safe. Live long and prosper. |
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| Grogster Admin Group Joined: 31/12/2012 Location: New ZealandPosts: 9082 |
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| CaptainBoing Guru Joined: 07/09/2016 Location: United KingdomPosts: 1995 |
that little gadget you made is going to earn its keep! A great addition to the test gear in your lab (and several others I suspect ) I would be tempted to bolt on a MM and have it run a series of tests just to give a Go/NoGo indicator as a complete stand-alone box. |
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MicroBlocks Guru Joined: 12/05/2012 Location: ThailandPosts: 2209 |
@Grogster, Could you measure the HC-12 module. I am busy with the tibbit enclosure and i think it will fit nicely when i include a footprint for such a module. I have ordered some but the sooner i get the dimensions the better.:) ONLY when you have time of course!! Microblocks. Build with logic. |
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| Grogster Admin Group Joined: 31/12/2012 Location: New ZealandPosts: 9082 |
@ CaptainBoing - Now that's an idea! Hmmmmmm.........  @ MicroBlocks - Here you go:  I cropped this image from one of the listings on AliExpress. Smoke makes things work. When the smoke gets out, it stops! |
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