The enclosure revision failed as a verification artifact, not necessarily because the overall v2c enclosure concept is wrong. The generated views were not reliable enough to prove that the selected parts, cables, and service motions physically fit, so I did not use them to authorize PCB changes.
What is resolved
The UI architecture is now clear:
The OLED and pushable encoder will share J9’s 3V3, GND, I2C_SDA, and I2C_SCL.
A smart I²C encoder avoids adding raw encoder A/B/push connections to the PCB.
The approved visual direction remains the screw-joined translucent enclosure with exposed controls, a guarded tube hatch, and a removable rear panel.
What remains unresolved
OLED mounting
The candidate OLED PCB is about 29.2 × 26.7 mm.
The existing 36 × 24 mm opening is too large to retain it directly.
It therefore needs a carrier or bezel with verified screw locations, display alignment, panel thickness, and cable clearance.
That bezel would be visible, so it must be shown accurately before changing the detailed enclosure.
Encoder mounting
The encoder electronics are suitable in principle, but the complete mechanical stack is not qualified.
We need to verify the threaded bushing, washers and nut, panel opening, 3 mm panel thickness, remaining shaft length, knob engagement, and push-button travel.
Without this, the knob might rub the panel, sit too far out, or lose its push function.
Rear power inlet
A specific threaded panel-mount DC jack still needs to be fixed.
Its cutout, anti-rotation feature, nut clearance, solder-terminal depth, plug overmold, cable bend radius, and disconnect arrangement must fit the removable rear panel.
Rear-panel removal must not pull directly on solder joints or require cutting wires.
Heater and thermal wiring
The heater block and tube holder are custom mechanical assemblies, not components already represented on the PCB.
The exact heater cartridge, block dimensions, thermal cutoff mounting, NTC packaging, thermocouple junction, strain relief, and thermal isolation still need qualification.
The proposed fine thermocouple wire is not directly compatible with the existing JST-XH contact range, which expects substantially larger conductors. A mechanically sound transition is required.
Cable and service sweeps
We have not yet demonstrated that all plugs can be inserted and removed.
Cable bends must avoid the PCB, supports, hatch, optical chamber, and hot surfaces.
The rear panel must be removable with sufficient service slack.
The PCB/base assembly must remain removable without trapping the UI, power, heater, or sensor harnesses.
Why PCB routing is still on hold
The connector positions determine where the harnesses enter the enclosure and how much bend space they require. If one of those connectors needs to move after routing cleanup, the newly routed copper may need to be discarded.
Once those positions are mechanically frozen, I can make a surgical cleanup around U5, R9, R10, and D4 while preserving unrelated copper. That work will particularly address the wide HEATER_LOW_SIDE trace passing R10 with only about 0.36 mm local copper separation. It technically passes the present clearance rule, but it is poor margin in a noisy switching area.
So the current status is: the electrical UI strategy is selected, but the exact mounting and harness geometry are not yet proven. The PCB has deliberately been left unchanged until that proof is available.
Input: 12 V nominal from a certified external adapter.
Heater rail: protected 12 V direct to resistive heater through a low-side MOSFET.
Logic rail: 12 V to 5 V/3.3 V buck conversion; final topology depends on the selected controller module and peripherals.
No battery or internal mains.
Estimated Loads
Values are conservative architecture estimates pending exact component selection. The logic rail must be recalculated from datasheet maximums after the controller module, buck regulator, OLED, sensor, illumination LED, buzzer, and any memory are selected.
Table
Rail
Load
Typical
Peak
Notes
12 V
Resistive heater
8–15 W average after warm-up
20 W
PWM controlled; 1.67 A at 20 W
3.3/5 V
MCU/controller
40 mA
120 mA
Depends on module and service USB state
3.3 V
OLED
15 mA
35 mA
Content-dependent
3.3 V
RGB/clear sensor
2 mA
5 mA
Excludes illumination LED
3.3/5 V
Controlled LED
0–10 mA
30 mA
Pulsed during measurements
3.3/5 V
Buzzer and indicators
0 mA
35 mA
Short duration
3.3 V
Encoder, lid switch, memory
2 mA
10 mA
Combined estimate
Rail Totals
Heater peak: 20 W / 12 V = 1.67 A.
Logic/peripheral peak estimate: approximately 0.8 W.
Reflected to 12 V at 85% conversion efficiency: 0.8 W / (12 V × 0.85) ≈ 0.08 A.
Total expected input peak: approximately 1.75 A.
Add controller, wiring, tolerance, startup, and heater margin: design for 2.25 A minimum.
A possible future lid heater, provided the total budget is recalculated first.
Heated-Lid Contingency
A heated lid is not part of the baseline Rev 1 schematic. If liquid-dummy testing shows unacceptable condensation or reaction-zone volume redistribution, add a separately sensed and switched lid heater only after recalculating the power path.
Preliminary contingency case:
Main block heater peak: 20 W.
Possible lid heater: 5 W peak.
Logic and peripherals: 0.8 W peak estimate.
Conversion and wiring allowance: approximately 2 W.
Total contingency peak: approximately 28 W, or 2.33 A at 12 V.
The 12 V, 3 A adapter remains plausible for this contingency, but the input connector, protection, fuse, wiring, MOSFETs, bulk capacitance, and enclosure thermals must be revalidated. A 105 °C lid profile, if required by a specific assay, needs its own sensor, cutoff strategy, material review, and safety analysis; it cannot share the 91 °C block thermal fuse.
Power-Path Ratings
Table
Element
Minimum Architecture Rating
Rationale
DC input connector
3 A continuous or higher
Matches adapter and margin
Input protection / fuse
Coordinate for ~2.25 A design load and 3 A source
Final type depends on heater inrush and ambient temperature
Reverse-polarity stage
4 A, low loss
Avoid excess heating and voltage drop
Heater MOSFET
≥30 V VDS, low RDS(on) at actual gate voltage, ≥5 A thermal capability
Margin over 12 V/1.67 A load
Heater wiring/connectors
≥3 A at operating temperature
Heater compartment runs warm
Buck regulator
≥1 A output
Large margin over estimated logic peak and supports development accessories
Bulk input capacitance
Sized after PWM frequency and wiring tests
Limit rail bounce from heater switching
Thermal Checks
A 20 mΩ MOSFET at 1.67 A dissipates about 56 mW before switching loss; a poor 150 mΩ device dissipates about 0.42 W and is undesirable.
A linear 12 V to 3.3 V regulator is not acceptable for the full logic load. At 100 mA it would dissipate 0.87 W; use a buck regulator.
Heater PWM must not cause brownout or visible OLED flicker; separate high-current return routing and local bulk capacitance are required.
Operating States
Table
State
Estimated Input Power
Idle/UI
0.5–1.0 W
Warm-up
20–22 W
Hold at 65 °C
Approximately 8–16 W, environment-dependent
Fault/cooldown
0.5–1.0 W with heater forced off
Open Measurements
Actual heater resistance versus temperature.
Heater duty cycle at 65 °C in the final enclosure.
Exact logic-rail peak from selected-part datasheets, plus buck efficiency and quiescent current.
Cable and connector voltage drop at full heater power.
Whether condensation control requires an additional lid heater.
Decision
Use a 12 V, 3 A certified adapter architecture for Rev 1. Recalculate the complete budget before adding a lid heater, fan, battery, USB-PD input, or multiple reaction wells.