Sensor modules

AXS-035 — MAX31855K thermocouple front end PMOD module

Catalog #35, level L3 (read-only SPI).

Level L3 ERC clean DRC clean Fab package 7 components

3D render of the AXS-035 PCB — Rendered from the PCB layout. No physical board has been manufactured.

Components#

Every placed component, with the reason it is on the board. Extracted directly from the schematic, so this cannot drift from the design.

Ref	Value	What it does on this board	Part number	Footprint
`C1`	100nF 16V X7R	Supply decoupling	`GRM188R71C104KA01D` Murata	`C_0603_1608Metric`
`C2`	10nF 50V C0G	Differential filter across the thermocouple inputs (datasheet recommendation)	`GRM1885C1H103JA01D` Murata	`C_0603_1608Metric`
`J1`	PMOD PLUG 2x6	PMOD peripheral plug (Digilent spec 1.2)	not selected generic	`PinHeader_2x06_P2.54mm_Horizontal`
`J2`	TYPE-K TC	Thermocouple terminal: 1 = T+ (yellow, K), 2 = T- (red, K)	—	`TerminalBlock_Phoenix_MKDS-1,5-2-5.08_1x02_P5.08mm_Horizontal`
`R1`	100R	Series protection on the sensor-driven data line	`RC0603FR-07100RL` Yageo Datasheet ↗	`R_0603_1608Metric`
`R2`	10k	~CS idle pull-up so the output stays released until the host selects it	`RC0603FR-0710KL` Yageo Datasheet ↗	`R_0603_1608Metric`
`U1`	MAX31855K	Type-K thermocouple to digital converter with cold-junction compensation	`MAX31855KASA+` Analog Devices Datasheet ↗	`SOIC-8_3.9x4.9mm_P1.27mm`

Signals#

Net labels used in the schematic, which are also the names the HDL top level should use.

3V3 CS_N GND MISO SCK TC_M TC_P TC_SO

Production status#

Schematic ERC	0 violations
PCB layout	complete
DRC	0 violations
Fab package	exported (24 gerbers + drill + CPL + BOM)
Fabricated	no — design stage only

Source: boards/sensor-modules/axs-035-max31855

Catalog #35 (../README.md), level L3 (read-only SPI).

Status: schematic generated, ERC clean (0/0), netlist reviewed. PCB layout not started. Not released.

What it teaches#

The simplest possible SPI device — no MOSI at all. ~CS low + 32 clocks returns a fixed frame: 14-bit thermocouple temperature, 12-bit cold-junction temperature, and open/short-to-GND/short-to-VCC fault bits. Clean bit-slicing and fault-handling exercise; measures real flames, ovens, and soldering irons up to +1350 °C.

Design#

MAX31855KASA+ (type K), SOIC-8; 3.3 V supply, 100 nF decoupling.
Thermocouple on a screw terminal (1 = T+, 2 = T−) with the datasheet-recommended 10 nF differential filter.
SO through 100 Ω series to PMOD 3; ~CS pulled up 10 kΩ.
Layout note: keep J2 and U1 close and isothermal for cold-junction accuracy; the datasheet suggests a ground-pour thermal island.

Regenerate / remaining#

python3 generate_design.py — then PCB layout, HDL, BOM check, checklist.