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Azure
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Posted: 20 April 2018 at 5:53pm | IP Logged Quote Azure

@Palcal

Pogo pins came from bed of nails test rigs. Back when PCBs used to be expensive to make and most boards were sizeable. To make a test PCB was not a cost viable option a lot of the time.

Instead they would make a test jig (there were modules sort of like meccano/lego) that you could use to hold the test pins or (hopefully properly) drilled baseplates, made from various insulating materials. These were then hand wired up to a harness which was then wired to test connectors and/or connected to the testing system.

For large production runs these systems were also automated and the test jig could be swapped (hence the connectors) for testing different boards with a smart(er) testing system controlling and checking it all.

Ahhhh, that takes me back down memory lane :)


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Posted: 20 April 2018 at 9:44pm | IP Logged Quote Grogster

I have finished testing all the modules I could locate here from that November batch, and ALL of them have the same frequency error, so it is not just one or two.

That's thirteen modules out of fifteen, all work, but all are 37kHz off frequency.
I have yet to find the last two - I can't remember where I installed those ones, but I guess it will come back to me given time....

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Posted: 21 April 2018 at 12:28am | IP Logged Quote CaptainBoing

Grogster wrote:
I have finished testing all the modules I could locate here from that November batch, and ALL of them have the same frequency error, so it is not just one or two.

That's thirteen modules out of fifteen, all work, but all are 37kHz off frequency.
I have yet to find the last two - I can't remember where I installed those ones, but I guess it will come back to me given time....


That's not nice

Prolly keep them (well marked) for one-offs... like a fancy doorbell or something for your neighbours. (on a channel way-up so your stuff doesn't get swamped )

what a pain! HC-12a
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Grogster
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Posted: 21 April 2018 at 11:16am | IP Logged Quote Grogster

I have had confirmation from the PICAXE forum, that at least one other person is seeing this issue with their modules:

reginald on PICAXE forums wrote:
I have got a network running at about 500m between my PC and some outbuildings comprising of four modules plus one on the PC. Everything works fine at 1200 baud and I can see the data go back & forth as expected. Use a extra comm port parallel to the PC module on my PC and the none of the four 30mhz mods will receive the data though the network is still running fine swap to the three T300 I have got and they all work fine. I have no doubt that there is a problem if you mix the types. I can reproduce it every time. The only thing I haven't tried is testing 30mhz with 30mhz over the distance because my modules are soldered in.


I am trying to find someone local here, who is fluent in Chinese, who can help me correctly translate the hc01 webpage, and perhaps even establish contact with them on my behalf. Oh how I wish they had an English version of their site.
I would order direct from them to be sure of the genuine article, but navigating the Chinese language is a big brick-wall for me.

Edited by Gizmo on 22 April 2018 at 3:08pm


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Posted: 21 April 2018 at 12:14pm | IP Logged Quote Boppa

Jeez, havent seen a pogo stick for years, we had a couple of different types at a place I used to work at, one for testing pcbs after manufacturing (that basically tests the tracks for continuity/shorts before any components were mounted) and others for testing after being populated, where you could test the pcb without having to wire it up, and had breakout points for testing (frequency, voltages etc)

Very handy they were

One of the biggest issue with cheap pins was they would not always make reliable connections (remember they only work on pressure for conductivity) and cheap tinned (or even untinned!) pins could make intermittent contact, giving rise to false readings and sending you off on a wild goosechase looking for a non existent fault
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Posted: 21 April 2018 at 1:03pm | IP Logged Quote Quazee137


Odd though is if the problem is with a clock function register in the
RF chip not being set.

Can it maybe set by taking over the SPI interface and talking to it with a mite.

Quazee
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Posted: 21 April 2018 at 1:13pm | IP Logged Quote Grogster

@ Boppa(and WW) Re. Pogo pins: Now I can see why they might give trouble. I will get some genuine ones from Element-14/Mouser/Digi-Key etc.

@ Quazee137: What we need to know, is if the clone ones crystal is really off frequency. I have asked Phil on the PICAXE thread, if he would be willing to test one I send to him as he has tested a working one already. I would be very interested to know the results. I will let the thread know if he replies over there.

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palcal
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Posted: 21 April 2018 at 3:27pm | IP Logged Quote palcal

The ones you got certainly sounded the real deal,

...Barrel: phosphor bronze, gold plated
...Spring: music wire, gold plated
...Plunger: heat treated beryllium copper
But do we believe them.
Paul.

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Posted: 22 April 2018 at 12:14pm | IP Logged Quote Grogster

reginald on the PICAXE forums wrote:
So tonight I took two defunct HC-12 -T300 and took the crystals off. Took two good HC-12-30.000MHZ that won't receive properly took the crystals off and replaced them with the T300 crystals. Guess what they now receive correctly. Straight away no coaxing. Found out the the T300 are made by TCX below is link to a spec sheet for a 27MHZ crystal which is marked as T270 so I guess it is the same as the T300 -30.000MHZ. The only problem now is the 30.000MHZ crystals have no manufacturer mark so I can't get the spec for them. Still shows where the difference is. Perhaps it is the tolerance or the stability.


TCX Link

The plot thickens, and the crystal would seem to be our problem child.
I would consider replacing the crystal and using the clones, but I am not really that comfortable trying to force cloned modules into working, as the silicon used for the MCU and RF chip are probably also cloned, and could be unstable.

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Posted: 25 April 2018 at 11:20am | IP Logged Quote Grogster

Having a wee look around now for a fall-back plan if I am sent clones. I will strive to only use genuine, but once clones infest the market, it is gonna get harder and harder to spot the genuine ones, or for that matter, convince the sellers that they have sold us clones at all in the first place.

As the crystal seems to be the source of the main problems with the clones, I note that you can get a genuine TXC crystal from Element-14 for NZ$1.50 each, so I am tempted to buy in ten or twenty. Putting a genuine accurate crystal on the module SHOULD restore it back on frequency, but I think I would need to run a test or two.

Knowing that it would still be a clone - albeit a modified clone - I would still be unwilling to use them, as the other parts are probably sub-standard. Still, for a test to see what happens, I might follow in Reg's footsteps and replace the crystals and see if the frequency comes back in line with where it should be.

Replacing this tiny crystal could prove to be a pain in the arse. I would have to do one to see. Reginald over at the PICAXE forums managed to do it, so it can't be impossible.

TXC crystal at Element-14

Edited by Grogster on 25 April 2018 at 11:29am


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PeterB
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Posted: 25 April 2018 at 6:04pm | IP Logged Quote PeterB

G'Day Grogster
Is it possible that this consistent 30 MHz difference is the result of using Rx Xtals in a Tx. From my very limited experience of radio control they use Xtals that are 10.7 MHz apart, 10.7 MHz being the IF.
Peter
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Posted: 26 April 2018 at 8:38am | IP Logged Quote Grogster

Oh, ANYTHING is possible, Peter!
It would not surprise me in the slightest if that was the case, especially if RX crystals are cheaper by a cent or two, those would be the ones the cloners would use.
As far as these kinds of SMD crystals are concerned, I though a crystal was a crystal was a crystal - so long as it's frequency is accurate.

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