How do I take an nrf52840 Devkit prototype to custom PCB

[davidm]

Hi all

I am working on Bluetooth application using NRF52840 kit. The application is very simple, the device would have about 7 push buttons which when pressed data will simply be  sent to the nearby connected peer device. I am planning to take this to production soon, so I am trying to figure out the how to get started on the schematic and BOM list. But I am not very clear with the process of taking it from Devkit prototype to custom PCB for Nordic/nrf52 products. I came across a  reference layout for nrf52840  and I know the next step is to create the schematic but still, I am not sure how to proceed from here. In addition to nrf52840 SoC, the other components needed for my custom device  are 7 push buttons, 8 10K ohm resistors, and 1 led.

For now, I have one question, based on my needs how do I proceed from here(create schematic and find BOM list)?

Thank you in advance

[Andreas]

Hi,

 

You can download the reference layout and schematic and use that, so you do not have to add the nRF52840 with support passives manually. There is a download in the link you referenced. Buttons, and resistors are added to the GPIOs just as you did in your devkit prototype. There are also some Eagle libraries here, if you prefer that.

You can also use a 3rd party module, simplifying PCB design.

 

Best regards,

Andreas

[Nguyen Hoan Hoang]

I would recommend using existing certified module like this one https://www.crowdsupply.com/i-syst/blyst-nano.  It would reduce a of development time and reducing risks.  The module has everything builtin 32768 Hz RTC crystal, DC/DC coils.  Only thing need to add is power.  Although this module is nRF52832 based, your application does not seem require a nRF52840.  It with work well without changing your code.  Just need to use with S132 instead S140. 

[davidm]

Thank you, Andreas, for the response and sharing the resources.The pre-certified modules sounds good, I was not aware of that.

So If I decide to go with pre-certified modules for example Fanstel BT840,that means I have to use their(third party) schematics/design not reference design provided by Nordic, is that correct?(Because I didn't see any schematic files on their website)

In both cases(Nordic IC and third party/pre-certified) how does the Antenna comes into the picture?

[Andreas]

Hi,

 

The 3rd party modules feature all necessary passives, the manufacturer will provide some reference design guidelines usually, but you mostly have to worry about power, positioning on your board, grounding of the module and keepout for the antenna. All this is described in the datasheet from the manufacturer.

If you use our SoC you have to implement the antenna yourself, this can be a little tricky if you do not have RF experience, but we have some material and try to offer as best support we can to lead you through this. It is not rocket science, just barely. This means you have more flexibility, which can be useful for a compact and/or densely populated design. With a 3rd party module you have to follow the mounting considerations/requirements from the manufacturer, if not you risk RF performance being degraded. If you follow the recommendations there should not be a whole lot of difference to performance.

There are different kinds of modules for different kind of mountings, some have an antenna onboard, some have a coaxial connector for use with an external off-the-shelf antenna. I suggest you spend a couple minutes browsing, and find a module that fits well with your plans and product.

 

Best regards,

Andreas

[davidm]

Thank you, Andreas.

Based on your explanation , it sounds like if you want to go to market sooner,and you are not very experienced in RF, it's better to go with third-party modules.Is that correct?

Are there any well known good modules?

Fanstel sells their module for $8 @ 1000pcs,with that price bump compared with Nordic SoC price per unit, do you think it's worth it ,from what I would have paid for certification costs with Nordic SoC ?