Can not find the device

RE: Can not find the device

nine-fox — Sun, 10 Sep 2017 05:08:56 GMT

Hi all, the pcb is redesigned and today I tested it.

Everything works well now. Main changes are:

The crystal is changed to 8pf
C1 = C2 = 12pf
REdesigned the RF to the 50ohm

I guess these points are really important to RF performance.Thanks everyone for your help! Really appreciated!

RE: Can not find the device

nine-fox — Sun, 10 Sep 2017 05:08:41 GMT

Hi Kristin, the pcb is redesigned and today I tested it. Everything works well now. Main changes are:

The crystal is changed to 8pf
C1 = C2 = 12pf
REdesigned the RF to the 50ohm

Thanks everyone for your help! Really appreciated!

RE: Can not find the device

FormerMember — Mon, 19 Jun 2017 08:29:29 GMT

The problem could be related to the layout. There are two main things in the layout that will create trouble:

1) The distance from the chip to the chip matching components: That distance should be exactly the same as in our reference layout.

2) Under the RF part of the layout, there should be a solid ground plane.

I would recommend you to read the tutorial "General PCB design guidelines for nRF52".

RE: Can not find the device

RK — Tue, 06 Jun 2017 12:50:50 GMT

@nine-fox AbystomaL is probably right as usual. One way, if you have any kind of signal analyzer (if you don't, get one) to check the crystal frequency is to write some code to output the TIMER clock divided down to 1MHz or something like that and use the signal analyser to measure it. Measuring it directly with an oscilloscope is tricky as the leads have capacitance so you have to switch out the load caps to compensate for that. You do certainly have some ground plane issues, it's swiss cheese on both sides of that board. I will say what Nordic would say if they reply, start with the reference design and don't deviate from it :) I did deviate from it but only because I can't hand solder 0402s (actually I can but it takes a long time). I wouldn't toss your board and buy new bits yet, you have something which runs, write some test code and test what you have until you know what's wrong.

RE: Can not find the device

AmbystomaLabs — Tue, 06 Jun 2017 12:41:01 GMT

The chip antenna isn't going to help out your problem. Your layout for the chip antenna is poor compared to the F hybrid. If the nRF is working you should be able to pick it at close range.

On the load caps, what I meant is that I believe 16pF is the wrong value. I reviewed the Nordic guidance and it didn't address the parasitic capacitance of the circuit. This will change the load caps by a few pF.

Do you not have just an oscilloscope to measure the frequency of the 32MHz with?

If you go through a re-design, you have very significant problems with your ground plane. It is broken in most areas under the nRF. This alone could cause the nRF to be unstable and not transmit.

Also, your schematic shows that you split the power and RF grounds. This is wrong for this device.

Happy to continue helping. But you are going to need to do a little testing a provide a little more feedback.

RE: Can not find the device

nine-fox — Tue, 06 Jun 2017 03:27:19 GMT

Hi Turbo, thanks for your answer. As I mentioned in questions, I removed the external crystal.

Also my code（thats 99% sample code） works quite well in Development board

RE: Can not find the device

nine-fox — Tue, 06 Jun 2017 03:24:36 GMT

hi guys, thanks very much for your comments. Still I cannot get it working...I will try the following things:

buy chip antenna and have a try
probably load caps are incorrect. I will buy again from another store
redesign the antenna layout

I will post when I have further info

RE: Can not find the device

RK — Mon, 05 Jun 2017 11:55:55 GMT

yeah he already said he did that.

RE: Can not find the device

AmbystomaLabs — Mon, 05 Jun 2017 11:47:01 GMT

I believe that was implied in item 1. Plus the sofdevice init would return a fault (ie, system reset) had nine fox not modified the init to use the internal RTC.

RE: Can not find the device

Turbo J — Mon, 05 Jun 2017 11:40:48 GMT

The NRF5x example codes require the 32768Hz quarz crystal. You omitted that, and thus need to modify the LFCLK configuration part in SOFTDEVICE_HANDLER_INIT(). Try using NRF_CLOCK_LF_SRC_SYNTH as source clock.

RE: Can not find the device

AmbystomaLabs — Mon, 05 Jun 2017 00:11:42 GMT

There are a few things:

Can you confirm your code runs and advertises correctly on a development kit? You only mention changing the RTC, but it is possible that something code related is wrong. And, a DK would quickly confirm this.
The backside of the meander F hybrid is supposed to be connected to ground. It tunes the antenna.
Is the pale blue layer on your artwork just the mask layer?
Finally do you have a way to confirm the frequency of your 32MHz? You can either measure with a calibrated o-scope or use DTM code to bring up the radio on a channel a measure the channel error.

As RK mentioned you can really mess up the antenna and you should still pick up the radio at close range as long as the chipset is functioning well with the bad load. My suspicion is that you are using the wrong load caps and the 32MHz is off frequency. This puts the RF off frequency by the same ppm.

RE: Can not find the device

RK — Sun, 04 Jun 2017 14:56:19 GMT

I doubt that, even if your components were a little wrong you'd get some radiation you could pick up . And connecting the antenna to ground is most definitely wrong. Connected to ground it's a wire, you need an antenna to radiate it has to be open-ended, balanced and tuned. I'm not entirely sure where you got that antenna design from, it seems a little long to me, but I'm not an expert in F-antennae. Normally somewhere around here either AbystomaLabs or one of the Nordic guys jumps in, they're quite good at this, I just know that connecting an antenna to ground is wrong. Do you actually have your antenna connected to the ANT pin? If so what component connects it? I start with a 0 ohm resistor and then tune from there.

RE: Can not find the device

nine-fox — Sun, 04 Jun 2017 13:23:57 GMT

Hi endnode, thanks for your comments. May I ask, is it ok? My current pcb antenna layout design? RK mentioned that RF is connected to GND. However, I tried to use a knife to cut that line connecting to GND. The problem still exists.

If nothing wrong in my current design, I am considering to re-buy all my electronic components and try again. I suspect some parameters of capacitors or else are not well-matched with the ones Nordic suggests

RE: Can not find the device

nine-fox — Sun, 04 Jun 2017 13:17:24 GMT

RTT works quite well and ....No, I didn't see any errors in RTT :(

RE: Can not find the device

endnode — Sun, 04 Jun 2017 09:08:45 GMT

Sorry, is RTT working but you just don't see any error or there is no debug output at all?

RE: Can not find the device

nine-fox — Sun, 04 Jun 2017 04:12:21 GMT

Well...I cut that line to GND, and the problem still exists :-(

RE: Can not find the device

nine-fox — Sun, 04 Jun 2017 04:01:25 GMT

Hi RK, thanks for your comments! Yes, currently antenna is connected to GND....so it should not? Wow....I do not know that. I will try to remove it and have a test

RE: Can not find the device

RK — Sun, 04 Jun 2017 02:56:08 GMT

Why is your meander antenna marked 'GND' on the gerbers? It looks (hard to tell from the jpg) that you have a via connecting the antenna to the back ground plane.