Hot!RN4871 the "brick" machine. Should I continue to develop it for production ???

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tssir
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2017/05/15 05:06:42 (permalink)
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RN4871 the "brick" machine. Should I continue to develop it for production ???

Hello,
First RN4871 works for a while. I manage to setup configuration and somes tests. After few days, it stop working. No radio and no serial response. Ok, maybe a mistake in configuration ...
Second works few hours. Bizarre ...
Third is "bricked" after very carefully use, and only one "$$$" sending. Now, led output blinking randomly (some time rapid blinking, some times off, some times on for ten minutes).
I think that the RN4871 die after receiving on RX. Because first one works well many days, without any communication to external CPU (solded and supplied on PCB, while developping other features). Problems comes with serial communications.
 
After some research, it seems that I am not the first to have this kinds of problems (this forum, for example). But the proposed solutions seems not "logical" or solid.
 
Has anyone ever used the RN4871 successfully in production ?
Because if it "brick" like that while developing, it is not reassuring for production !!!
 
#1

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    NKurzman
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    Re: RN4871 the "brick" machine. Should I continue to develop it for production ??? 2017/05/15 06:25:24 (permalink)
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    Does it need its firmware updated?
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    tssir
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    Re: RN4871 the "brick" machine. Should I continue to develop it for production ??? 2017/05/15 09:08:08 (permalink)
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    Last release is v1.18 from 27 september 2016, and release note shows nothing about this kind of problems. Someone says that firmware update is the right method to unbrick module (tested). But nobody says if it solve the problem. And i can not check version because immediate brick.
    It is why i am looking for some serious experiences with this module. I need evaluate if i continue with this module, or if it is too bad.
     
    Anyway it is not a solution for production, because i can't assume update of each new module.
    #3
    traversjames
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    Re: RN4871 the "brick" machine. Should I continue to develop it for production ??? 2017/05/18 02:26:12 (permalink)
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    I mentioned before about unbricking the module with a firmware update, but noted that it was probably my (ab)use of the module to cause it to become unresponsive in the first place.  Since I resolved all of the issues with UART comms and stable supply voltage I have been using the same module for weeks reliably with no issues.
    #4
    tssir
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    Re: RN4871 the "brick" machine. Should I continue to develop it for production ??? 2017/05/18 02:53:27 (permalink)
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    Thank you for informations. It is good news.
     
    I try a fourth module. I use 220 ohm isolation on each lines (except supply).
     
    First test : no communication, just supply.
    BT advertising works. Led blinks. But i notice a huge noise on TX (3.5v to 2.8v). I manage to add some small condensators, differents values, close to module supply line. The noise decreases slightly. But always abnormal.
    Same regulator and supply line is used for a Microchip CPU and a IMU chip (with decoupling condensator each). They keep working perfectly.
    But I will investigate about lack of dynamism of the regulator.
     
    Second test : reset by pin.
    BT advertising works. Led blinks.
     
    Third test : send $$$ and looking for prompt response.
    No response. No led blinking. No BT advertising (normal after a $$$). TX line seems very clean, now.
     
    Fourth test : reset by pin.
    No effect. TX keeps very clean. No led blinking, no BT advertising.
     
    The result is same as the third module : locked after first $$$.
     
    I would like to believe that the problem comes from my installation or my welds. But four modules ...
    I will try a SPBTLE module in same configuration.
    #5
    traversjames
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    Re: RN4871 the "brick" machine. Should I continue to develop it for production ??? 2017/05/18 04:57:42 (permalink)
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    I had some concerns about my own board and I ended up just wiring a module to a 3V battery (no supply noise) with a power decoupling capacitor and only TX and RX connected to a serial cable.  I made sure that the timing and data on RX were correct using an oscilloscope and waited for response from TX before sending any further characters.  When all of these were correct and verified the module worked fine - then you can go back to the original board and check for differences.
     
    I had to do a lot of modifications to my code to make sure all timing specs were met and responses received; e.g. after power-up and reset you need to wait 100ms before sending any characters and make sure the %REBOOT% string is fully transferred.
    #6
    boatbodger
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    Re: RN4871 the "brick" machine. Should I continue to develop it for production ??? 2018/03/13 15:37:45 (permalink)
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    I too have been experimenting with the RN4871 modules. 
    One I bricked rather permanently by accidentally allowing its supply to rise to 5V.  It got very hot, and I can't blame anyone but myself for that.  I bought three more.
     
    For the second, one I was being REALLY careful.  Ran it from its own 3.3V regulator, Ran the Rx/Tx lines via resistors to ensure they could not possibly go above 3.3V - verified with a DMM.
    This one responded just once to the $$$ command, but did not show up on my phone.
    That was it.  Bricked.  No response at all, not even to attempt to re-flash.
     
    I went through everything till I was blue in the face, and concluded there really really really was nothing wrong with the conditions, so put in a third module.
     
    It works perfectly.
     
    I now don't know whether I dare base a product on these things.  They seem very very flakey.
     
    I am now psyching up myself to see whether the fourth one I've bought is a good'un or not...
    #7
    RISC
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    Re: RN4871 the "brick" machine. Should I continue to develop it for production ??? 2018/03/13 17:01:47 (permalink)
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    Hi,
     
    Make sure to update the firmware of the RN4871 to v1.28.3 which solves probably this issue :
    http://www.microchip.com/wwwproducts/en/RN4871 (under the Documentation > software section at the bottom of the page)
    Release notes
     
    Regards
     
    #8
    boatbodger
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    Re: RN4871 the "brick" machine. Should I continue to develop it for production ??? 2018/03/14 02:18:03 (permalink)
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    I tried that, but the updating tool could not detect the BLE module.
    I was able to successfully update the firmware on a 'good' module using the same harness.
    I'd be happy to post the failed unit for examination if anybody is interested.
    Or perhaps it could be re-programmed using the pads underneath using JTAG or equivalent?
    #9
    boatbodger
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    Re: RN4871 the "brick" machine. Should I continue to develop it for production ??? 2018/03/15 02:03:21 (permalink)
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    Of my three units:
    Unit 1: Worked once (I saw the %REBOOT% message) and then permanently bricked - no activity on its TxD line even in "reflashing" mode, and no RF visible in "operating mode", therefore cannot re-flash.
    Unit 2: Worked to start with. 
    - Then I saw garbage coming out of the TxD line, with intermittent %REBOOT% messages occasionally
    - A reboot cleared that for 15 to 45 seconds  then it started again
    - Then it stopped working. 
    - I *was* able to reflash this one
    At this point, I considered my test harness again.  I had soldered "short" wires to the module to connect it as I'm still at 'breadboard' stage.  These wires are about 25mm long, so the nearest power decoupler was on a 50mm round trip.
    I estimate the inductance of the loop at around 40nH, giving stored energy of about 4picojoules.
    Is that really enough to fry the device?
    Whilst sceptical, I decided to "ugly" a 1uF chip cap directly across the power pins using 2.5mm long wire strands.  (Embarassment at my microsoldering capabilities prevents me from posting a picture)
    After that, Unit 2 appeared to work flawlessly
    Unit 3: I fitted the 1uF cap before doing anything else, and it has behaved flawlessly
     
    Tentative hypothesis: These devices have suicidal tendencies unless there's a good bit of capacitance very near their power terminals.
     
    #10
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