nRF51822 BLE Flex Module

nRF51822 implemenation of Smart Bluetooth with a large amount of GPIO, 3dB antenna and SWD connector. For sale on Tindie.

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The most recent implementation of the nRF51822 BLE Flex Module is based on the Molex 3dB antenna. It includes 7 analog input/GPIO and 13 GPIO castellation pins, 3 GPIO driving an optional RGB LED, a reset button, and a 32k crystal to reduce power consumption. The circuit is shielded, has separate ground planes, and has a ferric bead filter on VCC.

This is our main communication Flex Module. Bluetooth BLE will be the primary way to interact with all Flex Modules.

These boards are alpha quality, they will likely not work yet. The design is in DipTrace. The design will require some tuning. This module is an nRF51822 with balun and chip antenna. I wanted to work with normal board thicknesses instead of more common module designs around a PCB trace antenna which requires a much thinner board. I am testing with 1db, 2db, and 3dB chip antennas in a variety of layouts.

Programming is supported through SWD utilizing the 6-Pin Tag-Connect TC2030-IDC.

Design Notes:

Ground Stitching

2.45Ghz frequency has a wavelength of 12.08cm.
Recommended ground stitching distance is wavelength/20 or 6.04mm

Antenna Feedline

Johanson Technology recommends a coplanar waveguide
(Calculated using TXLine and OSHPark board specs):

4layer: dielectric constant 3.665, loss tang 0.012, copper, ~51ohm, 2.45ghz, height 6.7mil, thickness 1.4mil, gap 6mil = 11.2756mil

2layer: dielectric constant 4.6, loss tang 0.016, ~51Ohm, 2.45ghz, height 1.6mm, thickness 1,4mil, gap 6mil = 29.0102mil

The solder mask will lower the impedance slightly, so instead of 50Ohm, I calculated with 51Ohm.

I original attempted a microstrip design, but the width was around 110mil for 2 layer boards. Surrounding the trace with ground plane is much more sensible. The distance to the Antenna pad from the trace line is copied from the reference design. The balun should do most of the matching. I would recommend adding a microstrip for tuning, but until I have a chance to test with a Network Analyzer, it is pointless.

Any software related will be released under BSD or MIT license. SAAS or cloud based software will be AGPL.

Creative Commons License

  • 1 × NRF51822-QFAA-R Microprocessors, Microcontrollers, DSPs / ARM, RISC-Based Microcontrollers
  • 1 × EPSON FA-20H 16.0000MF12Z-AC (Q24FA20H00044) Crystal
  • 1 × EPSON FC-12M 32.7680KA-AC (X1A0000610008) Crystal
  • 1 × 2450BM14E0003 Balun
  • 1 × 2450AT43F0100 or 2450AT18B100 or Molex-47948-0001 Antenna

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  • OTA Updates

    Chris Hamilton09/01/2015 at 23:01 0 comments

    I have been working on the 128kB version of the nRF51822 chip, but it seems like the OTA versions of my firmware will not fit with the gcc toolchain. So, I will continue working with the 256kB version.

    Yageo has a new chip antenna coming out that is 2.7dB peak and still a small traditional chip antenna. I have had issues with the Molex antenna getting ripped off the board in some situations. So, when possible I will try the new antenna.

  • New revision

    Chris Hamilton01/21/2015 at 19:52 0 comments

    I have finally been able to update this board. The BiPower OTG and Qi/USB Charger modules are mostly done. So I know what the pin outs will look like (which held this board back). So I should be sending a new design with the 3dB antenna and shield to OSHPark this weekend. The design just fits the Tag Connect pogo programmer and antenna just outside the shield. I also added optional components - a reset button, an RGB LED (in shield), and a 32k crystal.

  • Design updates

    Chris Hamilton12/09/2014 at 13:44 0 comments

    As with all the other Flex Modules, I will be improving the castellation design shortly. In addition, I may try to add more GPIO pins. As the shield and the 3dB Molex antenna are similar heights, I can get away with closer trace routes with that antenna. So in addition to it being probably the highest gain chip antenna (especially for the price), it also improves the design. I'll also likely move to a 4 layer stack up, so I need to recalculate the co-planar waveguide. We should be able to start selling these when ready in the next month or two as a Flex Module is a "subassembly" not requiring certification. We will try to get it certified when it becomes popular.

  • Prefab shielding

    Chris Hamilton08/15/2014 at 22:14 0 comments

    Hi, we have been comparing footprints and placement.  At this point some of the smaller prefab almost fit, but not quite.  The big issue is the 2.54mm sized castellations.  They are too close for even the smallest shields.  Between that and antenna placement.  We may need to adjust the overall board layout.  Almost all common nRF51822 modules have shields, but they also have really poor antenna placement (according to manufacturer recommendations).  For now, we will not include component shielding.

  • Shielding

    Chris Hamilton08/11/2014 at 03:32 0 comments

    We will be modifying 0.9B before testing to support a pre-fab shield over the circuit. 

    Laird Technologies and LeaderTech both make reeled pre-fab shields that we will be evaluating.

  • Revision 0.9B

    Chris Hamilton08/03/2014 at 09:10 0 comments

    Just added some additional "thermal" vias, 3 additional GPIO, and additional VCC and GND to the 2dB version.  Sending out to OSHPark to test.

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