Sensor modules

AXS-031 — MCP3008 8-channel ADC PMOD module

Catalog #31 in the AruviX sensor line, level L3 (SPI). The classic MCP3008 8-channel 10-bit SAR ADC, with two onboard teaching loads and six channels on a breadboard header.

Level L3 ERC clean DRC clean Fab package 11 components

3D render of the AXS-031 PCB — Rendered from the PCB layout. No physical board has been manufactured.

Circuit review & bench-test guide →

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	VDD decoupling	`GRM188R71C104KA01D` Murata	`C_0603_1608Metric`
`C2`	100nF 16V X7R	VREF decoupling	`GRM188R71C104KA01D` Murata	`C_0603_1608Metric`
`C3`	1uF 10V X7R	Supply bulk decoupling	`GRM188R71A105KA61D` Murata	`C_0603_1608Metric`
`J1`	PMOD PLUG 2x6	PMOD peripheral plug (Digilent spec 1.2)	not selected generic	`PinHeader_2x06_P2.54mm_Horizontal`
`J2`	CH2-CH7 + RAILS	Breadboard header: CH2-CH7, GND, 3V3	not selected generic	`PinHeader_1x08_P2.54mm_Vertical`
`R1`	GL5528 LDR	Light-dependent resistor, ~10k at 10 lux	not selected generic	`R_LDR_D6.4mm_P3.4mm_Vertical`
`R2`	10k	LDR divider lower leg	`RC0603FR-0710KL` Yageo Datasheet ↗	`R_0603_1608Metric`
`R3`	10k	~CS idle pull-up so an unconfigured host cannot start a conversion	`RC0603FR-0710KL` Yageo Datasheet ↗	`R_0603_1608Metric`
`R4`	100R	Series protection on the ADC-driven DOUT line	`RC0603FR-07100RL` Yageo Datasheet ↗	`R_0603_1608Metric`
`RV1`	10k THUMB POT	Onboard load: full-rail pot, wiper to CH0	`TC33X-2-103E` Bourns Datasheet ↗	`Potentiometer_Bourns_TC33X_Vertical`
`U1`	MCP3008	8-channel 10-bit SAR ADC, SPI, 200 ksps	`MCP3008-I/SL` Microchip Datasheet ↗	`SOIC-16_3.9x9.9mm_P1.27mm`

Signals#

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

3V3 ADC_DOUT CH0 CH1 CH2 CH3 CH4 CH5 CH6 CH7 CS_N GND MISO MOSI SCK

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-031-mcp3008

Catalog #31 in the AruviX sensor line (../README.md), level L3 (SPI). The classic MCP3008 8-channel 10-bit SAR ADC, with two onboard teaching loads and six channels on a breadboard header.

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

What it teaches#

The canonical first SPI ADC transaction: start bit, single-ended/differential select, 3-bit channel address, null bit, then the 10-bit result — all in one ~17-clock ~CS frame. Channel multiplexing, throughput vs SCLK, and comparing 10-bit SAR results against the precision AXS-032 (ADS1115).

Design#

MCP3008-I/SL (SOIC-16). VDD = VREF = 3V3 (full scale is the rail), AGND and DGND both to GND. 100 nF on VDD and VREF plus 1 µF bulk.
Onboard loads: CH0 ← wiper of Bourns TC33X 10 kΩ thumb pot across 3V3/GND; CH1 ← LDR divider (GL5528 upper, MPN TBD, 10 kΩ lower leg) — turn the pot / shade the LDR and watch codes move.
CH2–CH7 on J2 (1×8 header) followed by GND and 3V3 for breadboard use.
~CS has a 10 k idle pull-up; ADC-driven DOUT passes a 100 Ω series resistor to MISO.

PMOD pin	1	2	3	4	5	6	7	8	9	10	11	12
Net	~CS	MOSI	MISO	SCK	GND	3V3	NC	NC	NC	NC	GND	3V3

Regenerate#

python3 generate_design.py

Remaining for release#

[ ] PCB layout, DRC, fab outputs
[ ] hdl/: SPI master + channel-scan FSM, ECP5 demo
[ ] Pin the LDR MPN (GL5528 is a generic type, quality varies)
[ ] BOM export and availability check, design-review checklist