Sensor modules

AXS-030 — Piezo contact mic PMOD module

Catalog #30 in the AruviX sensor line, level L4 (streaming acquisition). A piezo disc (contact mic) on a 2-pin header, conditioned into an ADS7042 12-bit 1 MSPS SPI ADC.

Level L4 ERC clean DRC clean Fab package 11 components

3D render of the AXS-030 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	AVDD/DVDD high-frequency decoupling	`GRM188R71C104KA01D` Murata	`C_0603_1608Metric`
`C2`	1uF 10V X7R	AVDD/DVDD bulk decoupling	`GRM188R71A105KA61D` Murata	`C_0603_1608Metric`
`D1`	BAT54S	Schottky clamp of the piezo node to the rails	`BAT54S,215` Nexperia Datasheet ↗	`SOT-23`
`J1`	PMOD PLUG 2x6	PMOD peripheral plug (Digilent spec 1.2)	not selected generic	`PinHeader_2x06_P2.54mm_Horizontal`
`J2`	PIEZO DISC	Piezo contact-mic disc terminal: 1 = signal, 2 = GND (disc brass)	not selected generic	`PinHeader_1x02_P2.54mm_Vertical`
`R1`	1M	References the piezo charge source to mid-rail	`RC0603FR-071ML` Yageo Datasheet ↗	`R_0603_1608Metric`
`R2`	1M	Mid-rail divider, upper leg	`RC0603FR-071ML` Yageo Datasheet ↗	`R_0603_1608Metric`
`R3`	1M	Mid-rail divider, lower leg	`RC0603FR-071ML` Yageo Datasheet ↗	`R_0603_1608Metric`
`R4`	100R	Series protection on the ADC-driven data line	`RC0603FR-07100RL` Yageo Datasheet ↗	`R_0603_1608Metric`
`R5`	10k	~CS idle pull-up so the output stays released until the host selects it	`RC0603FR-0710KL` Yageo Datasheet ↗	`R_0603_1608Metric`
`U1`	ADS7042	12-bit 1 MSPS SAR ADC, SPI-compatible cs-framed interface	`ADS7042IDCUR` Texas Instruments Datasheet ↗	`VSSOP-8_2.3x2mm_P0.5mm`

Signals#

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

3V3 ADC_SDO CS_N GND MISO PIEZO SCK VMID

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-030-piezo

Catalog #30 in the AruviX sensor line (../README.md), level L4 (streaming acquisition). A piezo disc (contact mic) on a 2-pin header, conditioned into an ADS7042 12-bit 1 MSPS SPI ADC.

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

What it teaches#

Streaming acquisition: the ADS7042 has no registers at all — every ~CS-framed 16-clock burst returns one 12-bit sample, so the fabric side is a free-running sampler FSM feeding a FIFO. Then DSP-in-fabric: envelope detection (rectify + leaky integrator), knock detection, and trigger thresholds on the sample stream.

Design#

Piezo disc attaches via J2 (1×2 header, value "PIEZO DISC", MPN TBD — any 20–35 mm brass piezo disc works).
The disc is a charge source: 1 MΩ (R1) references it to a 2 × 1 MΩ mid-rail divider (R2/R3) so both swing polarities digitize around mid-scale.
BAT54S series pair clamps the node to GND/3V3 — a hard knock can generate tens of volts open-circuit.
ADS7042IDCUR (VSSOP-8), AVDD = DVDD = 3V3 (AVDD is also the reference), 100 nF + 1 µF decoupling. AINM to GND (single-ended).
cs-framed read-only interface: no MOSI, PMOD pin 2 left NC. SDO passes a 100 Ω series resistor; ~CS has a 10 k pull-up so the output stays released until the host drives it.

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

Regenerate#

python3 generate_design.py

Remaining for release#

[ ] PCB layout, DRC, fab outputs
[ ] hdl/: ADS7042 sampler FSM, FIFO, envelope detector, ECP5 demo
[ ] BOM export and availability check, design-review checklist