piNail/HARDWARE.md

piNail Hardware (Prototype v2)

This file captures confirmed hardware details for the cigar-box prototype. Unknowns are marked TBD instead of guessed.

Prototype Summary

• Enclosure: cigar box with integrated monitor in lid.
• Input power: IEC C14-style AC inlet ("computer PSU" style).
• Runtime controller: Raspberry Pi.
• Heating channels: 2 coil channels (channel 2 wired but not yet validated in operation).

High-Level Power Architecture

AC input path

1. AC inlet -> WiFi power switch.
2. From WiFi switch output -> master mains switch for system.
3. Master switch output branches:
   • Branch A: to main DC switching PSU (powers Pi/control electronics).
   • Branch B: to per-channel heater paths.

Control electronics power (DC)

• Main DC PSU output provides control-side power for:
  • Raspberry Pi
  • Two thermocouple interface chips
  • Two SSR control sides
• Nominal rail appears to be 5V (TBD: confirm exact PSU output voltage/current).

Heater power path (per channel)

• After master switch, AC route per channel is:
  • fuse -> manual front-panel cutoff switch -> SSR load side -> coil connector power line
• The opposite AC pole is routed from WiFi switch output directly to coil connector corresponding pole.
• Ground/earth conductor is routed to coil connector grounds.

Channel/Signal Topology

• Each channel has:
  • Thermocouple input (via MAX6675-type board)
  • SSR-driven AC heater output
  • Manual front panel power switch in series with heater path
• Raspberry Pi drives each relay channel independently.
• Thermocouple boards are connected to Pi GPIO.

GPIO Wiring (Clarified)

• Thermocouple channel 1 (as originally noted): GPIO 5, GPIO 8, GPIO 7 (BCM numbering).
• Thermocouple channel 2 was written as 11,12,13; this has been clarified as physical header pins.
• Thermocouple channel 2 validated mapping:
  • Physical pins 11,12,13 => BCM 17,18,27.
  • Read test on BCM 17,18,27 returns valid MAX6675 words with open-thermocouple fault bit set when probe is disconnected (expected).
• Alternate interpretation (BCM 11,12,13) returned all-zero frames and appears incorrect for channel 2.
• Relay control (channel 2): GPIO 9 (BCM).
• TBD: confirm relay control GPIO for channel 1 in this dual-channel prototype wiring doc.
• Note: these dual-channel assignments differ from the current single-channel piNail2/config.json runtime pins.

Monitor Subsystem

• Separate 12V power supply for the built-in monitor.
• Short HDMI from Pi -> monitor.
• Monitor considered optional for future versions.

Grounding Notes

• Enclosure is non-metal (cigar box), so chassis bonding is not the main factor here.
• Coil grounds are connected.
• DC PSU ground is connected on the input-side ground scheme.
• TBD: provide explicit earth/neutral/hot naming by region and verify continuity paths.

Protection and Switching (Current Understanding)

• SSRs used for heater switching (TBD: exact model/rating).
• Fuses appear to be 1A glass tube, one per channel (TBD: verify rating + slow/fast blow type).
• Per-channel front switches are manual toggles.
• WiFi switch has onboard button and can keep networked power state independent of channel switches.

Operational Behavior (as built)

• You can power down Pi + nail supply via master mains switch while keeping WiFi switch infrastructure behavior available.
• You can cut each coil independently with front-panel switches without shutting down software.
• Channel 2 is wired but not yet fully tested under load.

Legacy/Prototype Context

• Prototype v1: external Pi setup (pinout/relay/thermocouple cable to Pi), no built-in monitor.
• Prototype v2: integrated Pi + wiring + optional integrated monitor.

Required TBDs Before Final Electrical Spec

1. Coil connector pinout (both channels, exact pin numbering/function).
2. Main DC PSU make/model and output spec (V/A).
3. SSR model and AC load ratings.
4. Fuse exact spec (amp, voltage, blow type, holder type).
5. Exact line/neutral/earth routing confirmation diagram.
6. Channel 2 validation checklist/results.