Solartron 7075 interface unplaced

Konnect implementation

Solartron 7075 interface designed with Konnect 0.13.0, an MCP server that drives KiCad 10.0.6 (live IPC to the open editors, with file-level tools for libraries and the schematic).

Design

• 74 × 74 mm two-layer board. J1, a vertical DD-50 male (CAX DP-G-50P-ZC-YCLS, LCSC C54573066), sits on the bottom face, plugs into the meter's SKB socket and holds the board by its jackscrews. J2, a vertical USB-B (TE 5787834-1), sits on the top face.
• Meter side (GND_ISO): five SN74LVC165A shift registers read the 50-way interface's BCD and status lines through 100k pull-down networks. Two 74LVC595A drive the command lines. An AMS1117-3.3 powers this side from a B0505S-1WR3 isolated DC-DC module.
• Isolation: six TLP2361 optocouplers carry the SPI-style links across a copper-free band about 4.8 mm wide. No net crosses the barrier.
• USB side (GND): RP2354A (internal flash), AP2112K-3.3, USBLC6-2SC6, BOOTSEL and RUN buttons, and an SWD header.
• Parts: KiCad's libraries, with LCSC numbers for every fitted part (the SWD header is optional and has none). KiCad has no DD-50, so its symbol and footprint are in the project library. The footprint follows the CAX part's drawing, checked against the DIN 41652 dimensions in Harting's catalogue. The project library also has a TLP2361 symbol with an inverting output.
• ERC: 0 errors, 0 warnings. DRC: 0 unconnected items and one cosmetic error: C17 pad 2 on the USB side, a ground pad with one thermal spoke where KiCad wants two, as in the first layout. The remaining items are warnings: footprints that differ from their library copies, silkscreen clipping, overlap and clearance, and a missing LCSC footprint field on the parity check.

Review 1: pin swapping

The shift-register and resistor-array pins were re-assigned to untangle the meter-side routing. The '165 inputs (D0–D7) are equivalent, as are the '595 outputs (QA–QH) and the elements of the 100k arrays. The swaps were therefore made both within each part and between identical parts.

• Each resistor array feeds one side of one '165. The 36 DVM outputs are taken in D-sub pin order, left to right. So the tracks run D-sub pin → array → '165 pin without crossing, almost all on the top layer.
• The '595 outputs follow the order of their D-sub pins. QA, the pin on the far side of the chip, takes the outermost signal.
• U16 D3..D0 keep the 0,0,1,1 signature. The SAMPLE line moved from U18 QE/QD to QA/QC. The schematic's serial-link note now carries the full bit map that the firmware needs.
• The '165 LOAD and clock pins (1 and 2) escape to vias above each chip and join on two bottom-layer buses. Ground "pockets" (a bar and via over each array's ground pads, and vias for '165 pins 8 and 15) were placed before routing, so the input bus routes around them.
• The meter side was re-routed with Freerouting on top of those fixed pieces. The USB side was re-imported unchanged.

Whole board: 1,660 → 1,275 track segments and 201 → 136 vias. fab/routing_before_after.png compares the meter-side routing before and after.

Review 3: moving parts

The meter-side parts were moved, and the pins re-assigned again to suit. This includes the swaps between parts offered in reply to review 2. The 36 DVM input tracks were laid out by a script, in one repeated pattern, instead of by the autorouter.

• U16, the '165 with only four DVM inputs, moved from the middle of the row to the right-hand end. The nine '165 input sides that carry DVM lines now sit side by side, 11.08 mm per chip, which is twice the pitch of the D-sub's groups of four pins.
• Each array sits directly under its four D-sub pins, turned so that its signal pads face the connector. The tracks drop straight into the pads. On the way out, the outer two leave from the ends of the array, and the inner two run between its two rows of pads to the ends. Each '165 side takes two tracks from outside the chip and two from under the chip body.
• All 36 input tracks are on the top layer except DD-50 pin 36, which sits directly above pin 3. It uses one bottom-layer track and a via.
• The '165 decoupling caps moved to the top of each chip, between its two sets of input tracks, with a via to a bottom-layer +3V3_ISO spine. C29 moved above the regulator to make room for U16. U19 turned round so that PRINT_LEVEL reaches its input directly.
• Both shift-register chains now run in board order. MOSI enters U18, U18 feeds U17, and U17 loops back into U16. The '165 chain runs U16 → U15 → U14 → U12 → U13 → MISO. CMD_RATIO_N moved to U18 QD, next to the other U18 outputs. The serial-link note in the schematic has the new bit map.
• The script also placed:
  • the LOAD, SCK and OE buses on the bottom layer under both '595s, with a riser down the left of the D-sub;
  • SCK down a free channel under U15;
  • SIPO_CH1 under the '595 bodies;
  • a +3V3_ISO rail along the top edge and another along the opto row;
  • SIPO_LOOP down the right-hand side;
  • the '165 chain and MISO in a channel under the chips.
• Freerouting routed the rest: MOSI, the '595 outputs and the opto links. The USB side is unchanged.

Whole board: 1,275 → 958 track segments and 136 → 110 vias. DRC lost Review 1's three starved thermals on the meter side (C24, C30 and C31). It gained eight silkscreen overlap warnings, where the moved caps' reference text overlaps the '165 outlines and C37's overlaps U19. Konnect has no tool to move reference text. The positions file was regenerated; the BOM is unchanged. fab/routing_review3.png compares the meter-side routing after Review 1 and now.

Notes on the tool

• Konnect's Specctra (Freerouting) export refuses roundrect pads, duplicate pad numbers and bottom-side footprints. Nearly every KiCad SMD footprint has roundrect pads. 15 stock footprints were therefore copied into the project library with rectangular pads. Routing-only variants were swapped in for the export and swapped back after the import: renumbered duplicate pads, and a front-side mirror of the bottom-mounted DD-50.
• The DSN export wrote each pin's rotation as an absolute angle, not relative to the footprint, so rotated parts had their pads turned twice and Freerouting reported 226 violations. The pin rotations were corrected in the scratch copy of the DSN. The session import then refused one part because the angles were written as 270 and −90, so those angles were normalised.
• Konnect has no tool to delete or move a via, or to delete a copper zone, and it deletes tracks one segment at a time. Its SES import also needs a board with no tracks, vias or zones. So re-routing after the pin swaps needed KiCad's own Edit ▸ Global Deletions, run in the GUI by screen control with the user's agreement. In Review 3 the same dialog was driven through the menu bar in the background. Each time, the whole board's copper was then re-imported through Konnect: the USB side unchanged, the meter side new.
• Konnect can move and rotate footprints but not their reference text, so silkscreen overlaps from moved parts stay as DRC warnings.
• KiCad's save rewrites the project's design rules and net classes, so the rules were re-applied before each DRC.
• The ground pours needed a lot of manual work: stitching vias, a ground-only Freerouting pass, a small grid router written in the scratchpad, and hand-placed thermal spokes.
• Freerouting 2.4.1 was downloaded with the user's permission and run both through Konnect and from the command line.

Session statistics

stats.py reads the session transcript, ~/.claude/projects/-Users-chris-repos-llm-circuitgen-tests/47e5c69c-808f-4cd7-8f0d-34a4d53529bd.jsonl. It takes everything before the export request (2026-10-15 18:44:30 UTC), prints the tables in CONVERSATION.md and writes calls.csv. The export itself ran in a resumed session, 3539381d-…, whose file starts with a copy of the original's later records. The original file is the complete record.

The review that followed ran in the same resumed session. review_stats.py reads that session's transcript from the first review comment to the review export request. It prints the review tables, writes review_calls.csv and, with --write-md, writes REVIEW_CONVERSATION.md. The resumed session writes no cost-state records, so the review figures come from the transcript's per-response usage and tool timings, priced at the published Opus 5.5 prices. REVIEW_CONVERSATION.md explains how each figure was measured.

• Totals (tokens, API time, tool time and cost) come from the last cost-state record before the export request. API calls are the 520 distinct assistant message ids; the usage-limit error message is not a call.

• Active time is measured from each typed message until the reply finished, giving four stretches.

  • Waiting for the user's answers to the two AskUserQuestion prompts (27 s and 2 min 14 s) is left out.
  • The 4 min stall between 20:52 and 20:57 on 2026-10-14 is left out. The session stopped after a tool result with no reply, and nothing ran until the user's "keep going".
  • Time waiting on background autorouter runs counts as active.
  • Each call is credited from its request (the record that triggered it) to the next call's request in the same stretch. The last call runs to the end of the stretch.
  • The 80 s compaction goes under Not attributable.

• Categories are set by call number in stats.py. Judgement calls:

  • The DD-50 footprint work (calls 43 and 68–71) is PCB. The search for a DD-50 drawing that came before it is Schematic & research, as part selection.
  • Everything from the schematic-to-PCB update (call 153) to the fabrication outputs (call 515) is PCB. That includes:
    • the rect-pad footprint copies, and pointing the schematic symbols at them;
    • the short replies to autorouter progress notifications;
    • the BOM export with the Gerbers.
  • Other covers:
    • creating the branch (call 1);
    • the two commits, the file send and the two summaries;
    • the connector status checks after "Continue" (calls 195–196).

• Prices. There are only two distinct cost-state snapshots, too few for a least-squares fit, so the published prices are used. They come from https://platform.claude.com/docs/en/about-claude/pricing, read on 2026-10-15.

  • Claude Opus 5.5, per million tokens: $4 input, $5 for 5-minute cache writes, $8 for 1-hour cache writes, $0.20 for cache reads and $20 for output. The full 1M context is at standard prices.
  • Claude Haiku 5.5 (the web-tool helper): $0.10 input and $0.50 output for prompts up to 100k tokens, plus $10 per 1,000 web searches.

  Every cache write the transcript logs is a 1-hour write, and the 5-minute and 1-hour writes are priced separately per call. Checked against the snapshots:

  Snapshot	Model	Reported	Published prices
  2026-10-14 21:05	Opus 5.5	$35.5377	$35.5377
  2026-10-14 21:05	Haiku 5.5	$0.0777	$0.0777
  2026-10-15 12:31	Opus 5.5	$112.1028	$112.1034
  2026-10-15 12:31	Haiku 5.5	$0.0777	$0.0777

  The $0.0006 gap in the second Opus snapshot is in usage the transcript doesn't log. Pricing that usage's cache writes as 1-hour writes slightly overstates it, which implies about 200 tokens of 5-minute writes.

• Not attributable is the counters minus the logged calls:

  • Opus: 6,153 input, 905,282 cache-write, 4,026,769 cache-read and 8,379 output tokens, or $8.24.
  • Haiku: 143,884 tokens from web search and fetch, or $0.08.

  The first snapshot matches the logged calls exactly, so all of the unlogged Opus usage comes after it. That is more than one compaction summary of a 969k-token context would use. The counters also show 52 s of API time on retried requests, which the transcript doesn't log either. These retries are the likely remainder.

• Thinking tokens are part of the output tokens, as in the API's usage fields.