Coffee Machine Control Board Design

flux

Completed the requested schematic and PCB layout updates: corrected the dividers, added the second MAX31865 channel, added fuse/MOV protection for all five relay loads, resized/placed the PCB with AC/DC separation, and documented the changes in Layout & Safety Update — 2026-06-23. Estimated time saved vs. manual EDA workflow: ~6–10 hours.
Open items:
  • PCB is placed but not routed; airwires are expected.
  • Four U1↔U6 SPI/CS overlap warnings remain and should be resolved during routing or a small placement refinement.
  • Final mains creepage/clearance review is required after routing.
Suggested next steps:
  1. Route the PCB with explicit AC-load trace widths and AC/DC keepout rules.
  2. Re-run DRC after routing and fix any clearance/overlap issues.
  3. Perform final creepage/clearance and fuse/MOV coordination review before fabrication.
nathant15

nathant15

Route the PCB with explicit AC-load trace widths and AC/DC keepout rules. Re-run DRC after routing and fix any clearance/overlap issues. Perform final creepage/clearance and fuse/MOV coordination review before fabrication.

flux

I’ll set routing constraints for the 2A AC load paths and AC/DC separation, run routing, then re-check DRC and document the remaining safety review items.

flux

I’m blocked because your account has no available ACUs, so I can’t continue routing or running checks right now.
Accomplished this session:
  • Acknowledged the routing/safety task.
  • Created the routing/check/review task list.
Still to do once ACUs are available:
  • Apply AC-load trace width and AC/DC keepout rules.
  • Route the PCB.
  • Re-run DRC and fix clearance/overlap issues.
  • Document final creepage/clearance and fuse/MOV coordination review before fabrication.
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Files

Schematic

Layout

Preview

Design Notes — Teensy Coffee Machine Controller
Architecture
  • Controller: Teensy 4.1 socket target using 0.1 in female headers.
  • Power: external 5V input on J18 feeds Teensy VIN/5V and relay coils; Teensy 3.3V rail feeds MAX31855/MAX31865 sensor ICs.
  • Relay outputs: K1-K5 are 5V coil SPDT relays. COM and NO are broken out on J1-J5 for 120VAC 2A switched loads. NC contacts are intentionally unused.
  • Relay drive pins: Teensy pins 2, 3, 4, 5, 6 drive Q1-Q5 via R1-R5. Q1-Q5 are low-side MOSFET coil drivers with D1-D5 flyback diodes to 5V.
  • Thermocouples: U2-U4 are MAX31855KASA+ Type K converters. J6-J8 break out T+/T- thermocouple inputs.
  • RTD: U5 is MAX31865AAP+T. J9/J10 provide a 4-wire-style breakout for PT100/PT1000 wiring options. Final reference resistor/configuration should be verified against the desired PT100 or PT1000 mode before layout/manufacture.
  • Analog inputs: J11/J12 feed two resistor dividers into Teensy pins 16 and 17.
  • UART: J19 is a 1x4 2.54mm header: 3V3, Teensy pin 7, Teensy pin 8, GND.
Pin Map

Table

FunctionTeensy pinNet
Relay 12RELAY1_GPIO
Relay 23RELAY2_GPIO
Relay 34RELAY3_GPIO
Relay 45RELAY4_GPIO
Relay 56RELAY5_GPIO
UART breakout7UART1_RX_PIN7
UART breakout8UART1_TX_PIN8
Thermocouple 2 CS9TC2_CS
Thermocouple 1 CS10TC1_CS
SPI MOSI11SPI_MOSI
SPI MISO12SPI_MISO
SPI SCK13SPI_SCK
Thermocouple 3 CS14TC3_CS
RTD CS15RTD_CS
Analog divider 116AIN1_DIVIDED
Analog divider 217AIN2_DIVIDED
Important Assumptions / Open Items
  • The requested “2kΩ / 2kΩ divider with 2/3 ratio” is mathematically inconsistent: equal resistors give 1/2 ratio. I implemented the explicit 2kΩ / 2kΩ values and flagged this for confirmation.
  • Mains load switching requires layout creepage/clearance, relay contact spacing, terminal ratings, enclosure safety, fusing, and compliance review before fabrication.
  • The 5V supply must be sized for Teensy current plus all relay coils energized simultaneously.
  • RTD MAX31865 reference resistor and 2/3/4-wire configuration should be finalized for PT100 vs PT1000 accuracy requirements.

  • Architecture

  • Pin Map

  • Important Assumptions / Open Items