Electronics Lab — Circuits

Test and measurement circuits for a physics lab bench, built bottom-up from a bootstrap PSU through the tiers laid out in docs/general_purpose_circuit_dependency.md. Spacetime research — experiments aimed at faster-than-light travel, with no fixed commitment to any one specific theory or approach — is the current driving objective and gets its own tier graph in docs/spacetime_circuits_dependency.md, but the general-purpose foundation underneath it — PSU tiers, protection, safety monitoring, signal conditioning, measurement tools — isn't specific to that goal and is meant to be useful on its own.

Each circuit gets its own top-level folder with a SPICE netlist, a generated schematic, and a breadboard wiring guide. Power supplies are grouped under power_supplies/; measurement/test tools are grouped under measurement_tools/; signal-conditioning building blocks (references, amplifiers) are grouped under signal_conditioning/; timing/waveform generators are grouped under oscillators/; other circuit categories (safety monitoring, etc.) get their own top-level folders as they're built.

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Schematics

Each project can render a schematic.png from its .spice netlist. schematic.png is not committed (see .gitignore) — it's a build artifact, regenerated on demand:

# from the repo root
python tools/spice_to_schematic.py oscillators/ne555_astable/ne555_astable.spice

Output is written as schematic.png in the same directory as the .spice file. tools/spice_to_schematic.py uses schemdraw to parse SPICE R, C, V, and D elements and render a schematic image.

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Running simulations

Every circuit folder has an ngspice .spice netlist. Run with ngspice -b to predict voltages and currents before building.

# from the repo root
ngspice -b measurement_tools/fuse_test_voltmeter/fuse_test_voltmeter.spice
ngspice -b measurement_tools/cd4066_switch_tester/cd4066_switch_tester.spice
ngspice -b power_supplies/psu_pico_rail/psu_pico_rail.spice
ngspice -b power_supplies/psu_ultralow_v1/psu_ultralow_v1.spice
ngspice -b power_supplies/psu_low_v2/psu_low_v2.spice
ngspice -b power_supplies/psu_3xaa/psu_3xaa.spice
ngspice -b power_supplies/psu_4xaa/psu_4xaa.spice
ngspice -b power_supplies/psu_medlow_usbc/psu_medlow_usbc.spice
ngspice -b signal_conditioning/voltage_reference_lm358/voltage_reference_lm358.spice
ngspice -b oscillators/ne555_astable/ne555_astable.spice

Run from the repo root. Each netlist prints an operating point at its nominal load, then sweeps the load resistor to show the V/I curve.

oscillators/ne555_astable/ (and any future circuit using a behavioral macromodel rather than plain R/C/V/D elements) prints gmin/source- stepping warnings during startup — expected for that kind of model, not a sign the result is wrong; see that circuit's own README § Simulate for why.

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Smoke-testing a circuit

Printing an operating point documents what a circuit should do; it doesn't check it. Every circuit folder also has a smoke_test.py that runs its netlist and asserts against real thresholds: no node exceeding a part's safe voltage, no resistor dissipating more than its rated wattage (where the resistor is an actual physical part — some netlists use Rload purely as a simulated stand-in for whatever gets attached later, which isn't a smoke risk on its own), and a functional check that the circuit actually does what it claims (a divider ratio within tolerance, a buffered reference holding steady under load, a switch reading unambiguously different when open vs. closed). tools/ngspice_runner.py holds the shared ngspice-invocation/parsing logic every smoke_test.py reuses.

# from the repo root
python measurement_tools/cd4066_switch_tester/smoke_test.py
python measurement_tools/fuse_test_voltmeter/smoke_test.py
python power_supplies/psu_low_v2/smoke_test.py
python power_supplies/psu_3xaa/smoke_test.py
python power_supplies/psu_4xaa/smoke_test.py
python power_supplies/psu_medlow_usbc/smoke_test.py
python power_supplies/psu_pico_rail/smoke_test.py
python power_supplies/psu_ultralow_v1/smoke_test.py
python signal_conditioning/voltage_reference_lm358/smoke_test.py
python oscillators/ne555_astable/smoke_test.py

Or run all of them at once with tools/run_all_smoke_tests.py, which finds every smoke_test.py in the repo so this list doesn't have to be kept in sync by hand:

# from the repo root
python tools/run_all_smoke_tests.py

Exits non-zero on any failed check.

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Circuits — built & bench-tested

Each of these has been physically assembled and confirmed against its main.py/smoke_test.py pass criteria on real hardware. Not committed to a breadboard permanently — once a circuit's bench check passes and nothing else currently under construction needs its wiring in place, its parts go back to inventory; the netlist/breadboard.md/smoke_test.py stay as the record for rebuilding it later, along with a breadboard.jpg photo of the as-built jig where one was taken (see each circuit's own README.md § Files).

Folder	Circuit	Tier	Bench-tested
power_supplies/psu_pico_rail/	Pico's own onboard 3.3V rail, ~100mA budget	interim bootstrap PSU	2026-08
signal_conditioning/voltage_reference_lm358/	LM358 unity-gain buffer holds a resistor-divider reference steady under load	tier1 REF	2026-08-27 — loaded reading within 0.23% of unloaded (±2% tolerance)
measurement_tools/cd4066_switch_tester/	Pico-driven bring-up jig for one CD4066B analog switch — confirms it passes/blocks before trusting it in a later design	component validation (ahead of tier9 MUX)	2026-08-28 — switch 1 (I/O A pin 1 / I/O B pin 2 / control pin 13) PASS on all 10 CD4066BCN units; switches 2–4 per chip not yet individually tested
measurement_tools/fuse_test_voltmeter/	Pico ADC probe across a battery→fuse→resistor loop; arm switch (GP15) gates trip/reset detection so battery connect/disconnect isn't misread as a trip	bootstrap / concurrent measurement tool	2026-08-28 — bench wiring has since diverged and trip detection is currently non-functional (no longer a blocker — polyfuses are now sorted via ammeter_10ohm/ammeter_1ohm below instead); see this circuit's own README § Current bench status for the full detail
measurement_tools/ammeter_10ohm/	Pico reads current (not just voltage) through a polyfuse under test, via a 10Ω shunt + slide-switch shorting jumper	polyfuse validation (bootstrap tier)	2026-08-30 — all 20 RXEF005 (50mA) polyfuses PASS (trip + reset confirmed per unit)
measurement_tools/ammeter_1ohm/	Same approach as ammeter_10ohm scaled for 500mA: ~1Ω jumper-chain shunt (see resistance_measurement/) + 1N5817 reverse-polarity diode on the high side	polyfuse validation (psu_low tier)	2026-08-30 — all 20 RXEF050 (500mA) polyfuses PASS (trip + reset confirmed per unit)
measurement_tools/resistance_measurement/	Voltage-divider jig (known 10Ω reference vs. unknown leg) for measuring a low-value resistance or checking continuity between two nodes	supporting tool for ammeter_1ohm; reused for continuity/troubleshooting checks (e.g. psu_4xaa)	2026-08-30 — jumper-wire chain measured at ~1.005Ω, stable across repeated readings
measurement_tools/raw_voltage_probe/	Plain averaged-voltage reader at GP26 — no resistance math, no divider assumptions; the calling circuit's own README supplies the target	general-purpose probe, split out of psu_4xaa 2026-09-07 for reuse	2026-09-07 — confirmed reading ~0V correctly with the psu_4xaa divider unpowered; a non-zero (~2.75V) target reading is still pending that circuit's own validation
power_supplies/psu_ultralow_v1/	Single AA + 50 mA polyfuse	psu_ultralow (bootstrap)	2026-08-30 — component-level validation complete: RXEF005 polyfuse PASS via ammeter_10ohm/ (all 20 units), AA battery holder ready per docs/inventory.md. The assembled PSU itself has not been separately re-probed as its own demo build (see fuse_test_voltmeter/README.md's test-vs-demo distinction)

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Circuits — designed, not yet built

Build order runs top to bottom: the voltmeter has to exist — and its own fuse-free sanity check has to pass — before it's trustworthy for sorting good polyfuses from bad, and a polyfuse has to be sorted good before it belongs in a PSU. See measurement_tools/fuse_test_voltmeter/README.md for the voltmeter self-check → bench-test-the-fuse-batch → demo-in-a-PSU sequence this drives.

Folder	Circuit	Tier
power_supplies/psu_low_v2/	2×AA + Schottky + 500 mA polyfuse	psu_low (RXEF050 polyfuse validated — see ammeter_1ohm/ above — and the wire-stripper blocker is resolved; not yet physically assembled)
power_supplies/psu_3xaa/	3×AA + Schottky + 500 mA polyfuse	psu_system (between psu_low and psu_4xaa)
power_supplies/psu_4xaa/	4×AA + Schottky + 500 mA polyfuse	psu_system (top of the plain-AA-series progression)
power_supplies/psu_medlow_usbc/	5V USB-C + 500 mA polyfuse + bypass cap	psu_medlow
power_supplies/psu_medlow_lm317/	SFE Breadboard Power Supply Kit — LM317 adjustable, 3.3V/5V-selectable	psu_medlow (alternative to psu_medlow_usbc; kit not yet ordered, not yet built — see docs/TODO-arcticoder.md)

Each of these (except psu_medlow_lm317, an on-order kit with no netlist of its own — see its own README) has a SPICE netlist, a generated schematic, a breadboard wiring guide, and a smoke_test.py, but none have been physically assembled with real components yet. The polyfuses they depend on are no longer the blocker — both batches passed validation via ammeter_10ohm/ammeter_1ohm above — so what remains is just the physical build. Everything else in docs/general_purpose_circuit_dependency.md / docs/spacetime_circuits_dependency.md (safety monitoring, most of tiers 1–9) hasn't been worked out to netlist stage at all — folders for those will show up here as they get one.

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Notes

• measurement_tools/fuse_test_voltmeter/, cd4066_switch_tester/, and signal_conditioning/voltage_reference_lm358/ are the circuits here with Pico firmware (main.py) checked in. For more capable Pico ADC work (filtering, calibration curves, noise characterization), see the sibling pico/ repo's measurement_tools/gpio_analog_sensing/ — that repo isn't limited to one project, so general-purpose Pico infrastructure lives there rather than being duplicated here.
• Getting the physical Pico talking to this PC (WSL + usbipd device attach, MicroPython firmware, installing/using mpremote) is documented once in the sibling pico/ repo rather than duplicated here — see pico/README.md § Running on real hardware. Needed any time you run one of this repo's main.py scripts against real hardware instead of just simulating.
• See docs/orders.md for what's actually been ordered/received from AliExpress, docs/parts_reference.md for pinouts/specs on those parts, and docs/inventory.md for the master parts/quantities list — shared with the sibling pico/ repo, which keeps a one-line pointer back to this file at pico/docs/inventory.md rather than its own copy (see docs/kb/repo_docs_conventions.md).

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Repo structure

measurement_tools/
    fuse_test_voltmeter/     Pico ADC voltmeter, validates polyfuses via USB (built & bench-tested; trip/reset short test still pending)
        fuse_test_voltmeter.spice
        schematic.png         (generated, gitignored)
        breadboard.md
        breadboard.jpg
        main.py
        smoke_test.py
        README.md

    cd4066_switch_tester/    CD4066B analog-switch bring-up jig (built & bench-tested)
        cd4066_switch_tester.spice
        schematic.png         (generated, gitignored)
        breadboard.md
        breadboard.jpg
        main.py
        smoke_test.py
        README.md

    ammeter_10ohm/           10Ω-shunt current-based polyfuse tester (built & bench-tested)
        main.py
        breadboard.jpg
        README.md

    ammeter_1ohm/            ~1Ω-shunt version for 500mA polyfuses (built & bench-tested)
        main.py
        breadboard.jpg
        README.md

    resistance_measurement/  voltage-divider jig for measuring an unknown low resistance (built & bench-tested)
        main.py
        breadboard.jpg
        README.md

    raw_voltage_probe/       plain averaged-voltage reader at GP26, no divider math (built & bench-tested; reused by psu_4xaa)
        main.py
        README.md

power_supplies/
    psu_pico_rail/            Pico onboard 3.3V rail, ~100mA (interim, built & bench-tested)
        psu_pico_rail.spice
        schematic.png         (generated, gitignored)
        breadboard.md
        smoke_test.py
        README.md

    psu_ultralow_v1/         single AA + 50 mA polyfuse (built & bench-tested — component-level)
        psu_ultralow_v1.spice
        schematic.png         (generated, gitignored)
        breadboard.md
        smoke_test.py
        README.md

    psu_low_v2/               2xAA + Schottky + 500 mA polyfuse (designed, not built)
        psu_low_v2.spice
        schematic.png         (generated, gitignored)
        breadboard.md
        smoke_test.py
        README.md

    psu_3xaa/                 3xAA + Schottky + 500 mA polyfuse (designed, not built)
        psu_3xaa.spice
        schematic.png         (generated, gitignored)
        breadboard.md
        smoke_test.py
        README.md

    psu_4xaa/                 4xAA + Schottky + 500 mA polyfuse (designed, not built)
        psu_4xaa.spice
        schematic.png         (generated, gitignored)
        breadboard.md
        smoke_test.py
        README.md

    psu_medlow_usbc/          5V USB-C + 500 mA polyfuse + bypass cap (designed, not built)
        psu_medlow_usbc.spice
        schematic.png         (generated, gitignored)
        breadboard.md
        smoke_test.py
        README.md

    psu_medlow_lm317/         SFE breadboard PSU kit, LM317 3.3V/5V-selectable (not yet ordered, not built)
        breadboard.md
        README.md

signal_conditioning/
    voltage_reference_lm358/  LM358 buffered voltage reference (built & bench-tested)
        voltage_reference_lm358.spice
        schematic.png         (generated, gitignored)
        breadboard.md
        breadboard.jpg
        main.py
        smoke_test.py
        README.md

docs/
    history.md                                  design conversation log
    general_purpose_circuit_dependency.md       general-purpose tier graph (PSU, protection, tiers 1-4/6/9, scope/logic-analyzer tiers M0-M5)
    spacetime_circuits_dependency.md            spacetime-specific tier graph (tiers 5/7/8)
    TODO-arcticoder.md                          human TODO: single active/blocked/backlog checklist for both graphs above, plus personal action items
    TODO-completed.md                           dated audit trail of TODO-arcticoder.md items once done — moved here, not deleted
    inventory.md                                master component inventory (moved from pico/docs/inventory.md 2026-09-07)
    orders.md                                   AliExpress order log (received / on order)
    parts_reference.md                          pinouts & specs for ordered parts without a datasheet on file
    manuals/                                    converted (markitdown) part manuals; source PDFs gitignored
    kb/                                         process notes for future LLM sessions, not end-user docs

tools/
    spice_to_schematic.py   generate schematic.png from a .spice file
    ngspice_runner.py       shared ngspice-invocation/parsing helper for smoke_test.py scripts
    run_all_smoke_tests.py  finds and runs every smoke_test.py in the repo