S2-LP Custom Board - Need help

[Silas Valera]

Posted on January 07, 2018 at 03:35

Hi

I have my custom RF board using S2-LP and balunBALF-SPI2-01D3 (

/external-link.jspa?url=http%3A%2F%2Fwww.st.com%2Fcontent%2Fccc%2Fresource%2Ftechnical%2Fdocument%2Fdatasheet%2Fgroup3%2Fe9%2Fff%2Fcd%2F1e%2F4f%2Fdd%2F49%2Fb4%2FDM00417488%2Ffiles%2FDM004174pdf%2Fjcr%3Acontent%2Ftranslations%2Fen.DM004174pdf

) and my custom board follows the evaluation design given in the balun data sheet. I am having problem with it:

The host controller communicates fine with S2-LP over SPI (I can see the expected signals on oscilloscope for SCL, SDI, SDI and CS). Also SMPS 1 and 2 (pins 2 and 3 of S2-LP) show expected waveforms. But there is not signal on TX pin. Can anyone help me please?

Thanks

Silas Valera

#868-mhz #custom-board #s2-lp #balf-spi2-01d3

Note: this post was migrated and contained many threaded conversations, some content may be missing.

[Igor Orlovich]

Posted on February 12, 2018 at 17:38

Did you actually configure it to go to CW mode? You need to configure radio settings, data source (PN9), modulation (or not) and go to TX mode before you'll see anything out of it.

[Silas Valera]

Posted on February 13, 2018 at 04:39

Hi Igor, 

thanks for your suggestions:) 

I am actually using the same code that is used in S2-LP DK 1.2.0 - SDK_Basic_Generic_A.c but only adopted for my microcontroller. I had actually tested my code using my controller and the S2-LP test board 

STEVAL-FKI868V1 - the eval board comes with STM32L1 Nucleo. I had tested this S2-LP board with my controller and it works fine. So I believe the code is fine.  I am trying to see if there is any hardware issue. 

Thanks again!

Silas

[Winfred LU]

Posted on February 13, 2018 at 06:46

Hi Silas,

If it is a HW issue, it will be worth to check 

http://www.st.com/resource/en/schematic_pack/steval-fki868v1_schematic.pdf

and please doubly check if everything is connected or soldered properly.

Best Regards,

Winfred

[Silas Valera]

Posted on March 13, 2018 at 02:39

Hi 

I did some redesign of the custom RF board, all capacitors in 0402 package, also using the 

BALF-SPI2-01D3 balun for 868Mhz. 

Now I have a different issue. With my custom microcontroller board, when I connect the 

STEVAL-FKI868V1 board using SCL, SDI, SDO, SDN, CS and GPIO3, the board transmitts fine (I am using Basic_Generic_A TX code) and on my other STEVAL-FKI868V1 kit (with nucleo) it receives fine and decodes the payload perfectly. But when I just replace STEVAL-FKI868V1 board with my custom RF board with my microcontroller board, I see that it transmits the signal but on the receiver STEVAL-FKI868V1 kit, it does not decode. I have attached the pic of RSSI with this. All other conditions remain the same (same modulation, data rate, bandwidth etc).

Where should I look? The balun could be the reason? Seems all the components are soldered as expected. Any help or suggestion?

Thanks

Silas

 

[Silas Valera]

Posted on March 18, 2018 at 01:47

Hi Igor,

Here is some more findings after I did some more test using CW mode

Coded for CW mode (no modulation) : Running the code for CW with S2-LP kit board with my controller board - and looking at the spectrum analyzer - it shows nice peak of -30dBm at 868Mhz, I have included the pic below. And then replacing the kit board with my custom RF board, I see no such peak for 868Mhz, but kind of spread, seems lot of harmonics, also included the pic below

Can this behavior be because of the balun 

BALF-SPI2-01D3 mismatch? Seems like there is no selectivity for the 868Mhz.  Can anyone help on this please?  Should I update my design to use the discrete components instead of the balun? The only benefit of using the balun is reduced component count and smaller PCB. I would really appreciate any of your feedback.. 

Thanks

Silas

[Winfred LU]

Posted on March 19, 2018 at 03:23

Hi Silas,

BALF-SPI2-01D3 is designed to match S2-LP 868MHz and 915MHz.

Some thoughts but i am not sure how much i can help:

Could you dump all the registers to doubly check if the custom RF board is configured exactly the same as EVAL board?

Is it possible to replace the receiver device (instead of the transmitting one) to your custom RF board?

Just to see if the custom RF board can receive well then the TX circuit will need to be checked.

Maybe it will be better to provide schematics and the board for some local FAE's reviewing.

Best Regards,

Winfred

[Silas Valera]

Posted on March 21, 2018 at 04:01

Hi Winfred,

Thanks for your replay and thoughts!

I have two S2LP eval kits - both for 868Mhz, So for one kit I replace the S2LP board with my custom board.Both configured the same as 2GFSK1/868Mhz freq/40Kbps datarate/20Khz freq dev/100Khz filter - I found the following:

1. My custom board as TX and kit as RX - no reception on rx side

2. My custom board as RX and kit as TX - no reception on my board side

3. My custom board configured for CW 10dbM - on kit side RSSI shows about -60dbM line

4. My custom board configured for CW / Max power - on kit side RSSI shows about -40dbM line

I have also attached the dump of registers from both my custom board and kit board. Seems only one value is different which is SYNT0 register, my board has 0x1F and kit board has 0x2F. I tried writing 0x2F to my custom board and running test, but no reception. Not sure why SYNT0 is different for my board, my board also has 50Mhz crystal. Let me know what you think..

I have also redesigned my custom board with discrete balun and sent out for fabrication. Should come back shortly. Meanwhile I will try to work on this version with BALF balun.

Thanks again for your valuable help!!

Silas

________________

Attachments :

Register_Setting_Kit.xml.zip : https://st--c.eu10.content.force.com/sfc/dist/version/download/?oid=00Db0000000YtG6&ids=0680X000006Hxr0&d=%2Fa%2F0X0000000b1d%2FeZPfyZVSdc0u1hwkCJ_mQnXXP6MMvcCQXmqZVvoYQqQ&asPdf=false

Register_Setting_Custom.xml.zip : https://st--c.eu10.content.force.com/sfc/dist/version/download/?oid=00Db0000000YtG6&ids=0680X000006Hxs7&d=%2Fa%2F0X0000000b1c%2FlgF_U7LUh.zUBHuUJRp1Z_7Rc7gDSteoNuXhgf3zihk&asPdf=false

[Anton Olofsson]

Posted on April 12, 2018 at 13:55

Hi Silas,

Hope you are making progress!

Have you double checked that TX-line between S2 and BALUN  is connected to SMPS2 as seen on p.5 here (VSMPS2):

http://www.st.com/content/ccc/resource/technical/document/datasheet/group3/e9/ff/cd/1e/4f/dd/49/b4/DM00417488/files/DM00417488.pdf/jcr:content/translations/en.DM00417488.pdf

 

Did using discrete components instead of balun help?

[Silas Valera]

Posted on April 13, 2018 at 04:04

Hi Anton, 

Thanks for your thoughts and suggestion! Yes I am following exactly the same schematic - the one in the updated version of balun reference manual.  I have actually compared the voltages between the S2LP Eval board and my board and they are similar. The one with discrete components also behaves similarly, get a very flat output and not a nice spike @868Mhz on spectrum analyzer. Both the versions are two layer pcbs and also I did not follow exactly the transmission tracks length guidelines, I was following the older version. But after that test, I have designed 4 layer pcb and have taken all possible care to follow the guidelines. My samples boards should arrive in couple of days. I am very much hiopeful this time  Will soon post the results! 

Best regards

Silas

[Silas Valera]

Posted on April 15, 2018 at 01:11

Hi All

I received my sample boards, this time with 4 layers and guidelines followed exactly, assembled one and tested!! Works perfectly fine!!   I compared with the S2LP EVAL board for the performance, and seems to give me almost comparable results! Both modes TX and RX work good. 

Thank you all!!

Silas

[Anton Olofsson]

Posted on April 16, 2018 at 08:33

Very nice to hear Silas!

To be honest i did not think it would be that sensitive to the layout.

Thank you for sharing and best of luck going forward!

Best,

Anton

[Silas Valera]

Posted on April 19, 2018 at 04:14

Hi Anton,

Thank you so much for your best wishes!

Yes, the RF PCB design is very much sensitive to many factors like component layout, components case/size, interconnecting traces, ground planes, ground vias, dielectric propperties of substrate, pcb thickness, Cu layer thickness etc.. There are many resources on the web for startup design and then fine tuning for best impedence matching for best sensitivity in Rx mode and max power tansfer in Tx mode. Generally transceiver IC manufacturer provides good guide lines and would give best results. Thanks to ST for the updated version for balun datasheet whichprovidesreference layout which makes the layout design very easy! Most important I think, is the microstrip width, there are online calculators available for this. Of course this

(

/external-link.jspa?url=http%3A%2F%2Fwww.st.com%2Fcontent%2Fccc%2Fresource%2Ftechnical%2Fdocument%2Fapplication_note%2Fgroup0%2Fdc%2F41%2F6b%2F68%2F62%2F9f%2F41%2Fd9%2FDM00341356%2Ffiles%2FDM00341pdf%2Fjcr%3Acontent%2Ftranslations%2Fen.DM00341pdf

)

guide is generally helpful too.

Best

Silas

[BMoha.19]

Hi @Silas Valera​ 

I can't display S2-LP register in my board (i can display them in ST eval board STEVAL-FKI868V2).

is there a specific configuration to dispaly S2-LP register soldered in my board?

Thanks in advance.

[Silas Valera]

Hi @BMoha.19​ 

I understand that yours is a custom S2-LP board. Please make sure the pcb design follows the guidelines. Do you use the balun or discrete components? In either case, make sure the S2-LP chip and components are soldered right and there is no bridge. With all the precautions/guidelines followed, your board should work as expected.

With you all the best!