Optional self-assembly with DigiKey parts

JLCPCB remains the primary route: order the existing assembled pill carrier, then fit the headers and modules using the assembly guide. Revision 0.0.5-dev adds shared-supplier switches and USB-C. Use matching revision files.

For self-assembly of the revised 0.0.5-dev board, use the separate DigiKey sourcing table and purchase CSV. The CSV gives exact cut-tape/tray order codes, reference designators, electrical specifications, original JLC identities, and installed quantities for one or five boards. It is a shopping list, not a JLC upload file.

What is covered

All 35 fitted SMT pieces are listed at DigiKey across 17 lines. The remaining-parts CSV now contains only its header. The two new MPNs require revision 0.0.5-dev; do not fit them to the prior board by assumption.

Commodity substitutions

• Resistors retain 0805 dimensions, resistance, ±1% tolerance and 125 mW rating. Bourns supplies the 5.1 kΩ USB-C pull-downs because the comparable Yageo cut-tape part was out of stock.
• Capacitors retain 0805 dimensions, capacitance, voltage rating, tolerance and dielectric. The 33 pF and 100 nF parts retain their exact original MPNs; the 10 µF and 1 µF selections use stocked equivalents.
• The Kingbright green indicator uses the existing 0805 lands and 560 Ω resistor. Match its cathode to native K/pad 1. Brightness differs by device; the illustrative current is about 4.2 mA at 5 V and typical forward voltage.
• Littelfuse SMF5.0CA retains the bidirectional 5 V stand-off, 200 W pulse class and SOD-123F package. It is transient suppression, not an overvoltage disconnect.

Each selected part links to its DigiKey page in the sourcing table. Stock was checked on 2026-10-17 and is not reserved. Prototype effective capacitance, LED brightness and powered behavior remain bench measurements, as with the JLC population.

Assembly process

Self-assembly of the whole carrier includes a 24-pin exposed-pad QFN, SMT card socket and two-sided population. A controlled paste/reflow process and inspection are appropriate; this requires more equipment and technique than the header soldering needed after JLC assembly. Use native paste, silk and placement information with the original reference designators. Replacements keep their existing footprints and net assignments; confirm LED polarity and IC pin 1 before heating.

After assembly, follow the staged rail and module checks, then reader bring-up. Use C&K PTS636SK25SMTR LFS and GCT USB4125-GF-A on revision 0.0.5-dev. USB4135 is not selected.

Use the enclosure hardware list when printing the case. M2.5 thread and spacer length alone do not establish clearance: a 5 mm-across-flats hex spacer has approximately 5.77 mm across corners and does not fit a 5 mm circular envelope.

See the dimensioned switch and USB-C comparison for the candidate land patterns, slot mismatch and button-height tolerance findings. The selected USB4125 and C&K switch have dedicated revised footprints. Physical fit remains unqualified.

Cost and button setup

The proposed 35-piece population costs $19.16 USD at exact one-board cut-tape/tray quantities, checked 2026-10-17; see variants/lcd-module-2.8/self-assembly/cost-estimate.json for every price and source. Excludes PCB, modules, headers, hardware, shipping, tax, tariffs and spares.

C&K height tolerance is ±0.2 mm. The SCAD button now has a measured-height parameter and a 0.15 mm gap, with 0.40 mm nominal total travel. Its conservative default assumes a 2.7 mm switch and avoids preload across the specified height range, but a shorter switch may not actuate. Measure each soldered switch and generate a matching plunger using -D button_switch_height=..., use the coupon for bore fit, then test travel in the assembled retainer. The parameter excludes print/solder variation and does not replace physical first-fit testing. Do not order eight identical default plungers assuming they work for every tolerance extreme.

Source: docs/SELF-ASSEMBLY.md ↗. Documentation describes reviewed evidence; it does not replace physical testing.