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Hardware

joric edited this page Sep 18, 2019 · 561 revisions

nRFMicro Features

  • Built in KiCad and fully autorouted with Freerouting (shouldn't be a problem to modify)
  • Same size as Pro Micro (18x33mm), has both MicroUSB and Type-C, Li-Po charger and BT 5.0
  • Runs full-featured QMK software (nrf52 fork), uses USB Mass Storage for firmware updates
  • Supports wired split keyboards via USB-C, MicroUSB and I2C/Serial TRRS extension cables
  • Supports fully wireless split keyboards over Bluetooth, does not need dedicated receivers

Bill of materials

You can use either Aliexpress or LCSC (the latter ships JLCPCB boards in the same box). Mind that LCSC doesn't usually have E73-2G4M08S1C modules and MSK-12C02 switches in stock.

The board schematic is available in the Releases section.

LCSC

There's an LCSC.com compatible BOM file in the Releases section.

Aliexpress

I'd really recommend Vanxy Aliexpress store instead of LCSC. Most components cost about $1, and for extra $1.47 they ship all in a single package with a trackable Aliexpress Standard Shipping.

Name LCSC PN Qty Package Value Description Aliexpress
U1 C331405 1 SMD 2G4M08S1C E73 nRF52840 $5-$7 / 1
J2 C165948 1 SMD MC-372 USB-C 16-pin $0.19 / 1
R2,R3 C14675 2 0603 100K SMD Resistor $0.61 / 100
R8 C98220 1 0603 10K SMD Resistor $0.61 / 100
R4,R5 C105580 2 0603 5.1K SMD Resistor $0.61 / 100
R1 C99782 1 0603 4.7K SMD Resistor $0.61 / 100
R6,R7 C22548 2 0603 1K SMD Resistor $0.61 / 100
D3 C84263 1 0603 Red SMD LED $0.87 / 100
D2 C84266 1 0603 Blue SMD LED $0.87 / 100
C1-C3 C1691 3 0603 10uF SMD Capacitor $1.69 / 100
Q1 C351408 1 SOT-23-3 AO3407 P-MOSFET $0.95 / 50
D1 C82544 1 SOD-123 1N5819 Schottky Diode $0.84 / 100
U3 C51118 1 SOT-23-5 AP2112K-3.3 VCC Regulator $0.81 / 10
U4 C14879 1 SOT-23-5 MCP73831 Li-Po Charger $1.02 / 10
Y1 C13712 1 TH 2*6mm 32.768KHz Crystal (opt.) $0.87 / 10
J1 C40943 1 5P 5P 4 legs MicroUSB (opt.) $0.46 / 10
SW1 C16168 1 SMD MSK-12C02 SPDT Switch $1.31 / 10
  • The 4.7K resistor (Li-Po current) can be replaced with 5.1K if you want to save money
  • Blue LED comes with Red LED (5 colors 20 pcs each, you also get other colors)
  • The 32.768 kHz external crystal is optional (QMK firmware does not use it)
  • MicroUSB is an option to replace USB-C (you can solder either of those)

SWD Programmer

You will need an SWD programmer to flash new bootloader (see Software). The best option is to get a Bluepill board (you will also need UART adapter to program it, if you don't have one).

PCB manufacturers

PCBS.io gerbers are now published on PCBS.io, so you don't even need to download anything. Takes about 9 days for the fabrication (black mask), ships with international USPS tracking number and costs $3.77 total, might be the best PCB manufacturer yet (for the small boards).

PCBS.io plot options (ONLY if you need to modify and reexport the board!)

Manually replace all oval pads with 4-5 round pads (PCBS.io needs round holes on the drill layer), and use the following plot settings:

  • disable "Edge.Cuts" layer, enable "Margin" layer (make sure it matches Edge.Cuts)
  • enable "Exclude PCB Edge layer from other layers", "Use Protel filename extensions"
  • (drill file) enable "PTH and NPTH in a single file"

Assembly guide (nRFMicro 0.03)

I pre-tin underside pads because boards are usually too oxidized to do that just with flux without rubbing the pads. The layer of solder should be as thin as possible to level the module without the gaps. No hot air gun is intended you simply heat them from the other side and pour more solder to the underside pin via those underside pin holes, if needed.

Li-Po battery uses RAW and GND pins (check for 4.2V charging voltage after assembly).

Avoid reverse polarity! If controller appears dead, replace 1N5819 or MCP73831, they fry first.

Testing

Testing firmware for nRFMicro 0.03 (upload this file with USB bootloader):

Connect any LED+ to VCC pin and test all the pins consequently via 1K resistor. LED should blink on all GPIO pins. If it doesn't blink, it's mostly bad soldering on the underside pins (maybe you forgot to pre-tin them), add more solder to the pads on the other side and heat them well to fill the gaps.

Red LED should blink if battery is not connected or the power switch is off, it's normal (it's wired directly to the charger).

Video

PnP assembly

Elecrow provides pick and place PCB assembly services for mass production. I haven't tried it yet, but it could be fun. See the example here (fully prepped Elecrow pcba spec in the repo):

Shipping log

Item Pcs Total Paid Shipped Received Days
SMDs from Vanxy 10 $11.38 2019-04-23 2019-04-27 2019-05-06 13
PCBS.io PCBs 0.03 4 $3.77 2019-04-23 2019-05-02 2019-05-14 21
2G4M08S1C Modules 2 $14.78 2019-04-23 2019-05-05 2019-05-17 24
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