Sensor modules

AXS-026 — Sound trigger PMOD module

Catalog #26 in the AruviX sensor line, level L1 (GPIO). Electret capsule → MAX9814 microphone amplifier with AGC → LMV7219 comparator with a trimmer-set threshold. The FPGA sees a clean digital SOUND pulse; the raw analog amplifier output is also brought out for scope probing.

Level L1 ERC clean DRC clean Fab package 20 components

3D render of the AXS-026 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	Microphone AC-coupling capacitor	`GRM188R71C104KA01D` Murata	`C_0603_1608Metric`
`C2`	470nF 16V X7R	MICBIAS bypass (datasheet typical application)	`GRM188R71C474KA88D` Murata	`C_0603_1608Metric`
`C3`	470nF 16V X7R	AGC attack/release timing capacitor	`GRM188R71C474KA88D` Murata	`C_0603_1608Metric`
`C4`	2.2uF 10V X5R	Amplifier DC-offset capacitor (datasheet typical application)	`GRM188R61A225KE34D` Murata	`C_0603_1608Metric`
`C5`	470nF 16V X7R	Amplifier bias bypass (datasheet typical application)	`GRM188R71C474KA88D` Murata	`C_0603_1608Metric`
`C6`	1uF 10V X7R	AC coupling from the amplifier into the comparator	`GRM188R71A105KA61D` Murata	`C_0603_1608Metric`
`C7`	1uF 10V X7R	MAX9814 VDD bypass (datasheet typical application)	`GRM188R71A105KA61D` Murata	`C_0603_1608Metric`
`C8`	100nF 16V X7R	MAX9814 VDD high-frequency decoupling	`GRM188R71C104KA01D` Murata	`C_0603_1608Metric`
`C9`	100nF 16V X7R	LMV7219 supply decoupling	`GRM188R71C104KA01D` Murata	`C_0603_1608Metric`
`J1`	PMOD PLUG 2x6	PMOD peripheral plug (Digilent spec 1.2)	not selected generic	`PinHeader_2x06_P2.54mm_Horizontal`
`JP1`	GAIN 50/40/60dB	MAX9814 gain strap: 1-2 GND 50 dB (default), 2-3 VDD 40 dB, open 60 dB	—	`SolderJumper-3_P1.3mm_Bridged12_RoundedPad1.0x1.5mm`
`MK1`	ELECTRET	Electret condenser microphone capsule, SMT, omnidirectional	`CMC-4013-SMT-TR` CUI Devices Datasheet ↗	`CUI_CMC-4013-SMT`
`R1`	2.2k	Electret bias feed from the MAX9814 MICBIAS output	`RC0603FR-072K2L` Yageo Datasheet ↗	`R_0603_1608Metric`
`R2`	100k	Comparator +in half-rail bias, upper leg	`RC0603FR-07100KL` Yageo Datasheet ↗	`R_0603_1608Metric`
`R3`	100k	Comparator +in half-rail bias, lower leg	`RC0603FR-07100KL` Yageo Datasheet ↗	`R_0603_1608Metric`
`R4`	100R	Series protection on the module-driven SOUND line	`RC0603FR-07100RL` Yageo Datasheet ↗	`R_0603_1608Metric`
`R5`	100R	Series protection on the module-driven SOUND_RAW line	`RC0603FR-07100RL` Yageo Datasheet ↗	`R_0603_1608Metric`
`RV1`	10k TRIMMER	Threshold-set trimmer across 3V3/GND, wiper to comparator -in	`TC33X-2-103E` Bourns Datasheet ↗	`Potentiometer_Bourns_TC33X_Vertical`
`U1`	MAX9814	Microphone amplifier with AGC and low-noise microphone bias	`MAX9814ETD+T` Analog Devices Datasheet ↗	`TDFN-14-1EP_3x3mm_P0.4mm_EP1.78x2.35mm`
`U2`	LMV7219	7 ns rail-to-rail comparator, push-pull output	`LMV7219M5X` Texas Instruments Datasheet ↗	`SOT-23-5`

Signals#

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

3V3 AMP_OUT BIAS CG CMP_IN CMP_OUT CT GAIN GND MICBIAS MICIN MIC_P SOUND SOUND_RAW THRESH

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-026-sound-trigger

Catalog #26 in the AruviX sensor line (../README.md), level L1 (GPIO). Electret capsule → MAX9814 microphone amplifier with AGC → LMV7219 comparator with a trimmer-set threshold. The FPGA sees a clean digital SOUND pulse; the raw analog amplifier output is also brought out for scope probing.

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

What it teaches#

The simplest possible sensor contract: a GPIO edge. Debouncing/re-trigger suppression in fabric, pulse stretching, and — via SOUND_RAW on a scope — what the comparator actually thresholds. The AGC makes the trigger respond to transients (claps, knocks) rather than absolute loudness.

Design#

CUI CMC-4013-SMT electret capsule, biased from the MAX9814's low-noise MICBIAS output through 2.2 kΩ (datasheet typical application), AC-coupled 100 nF into MICIN.
MAX9814ETD+ (TDFN-14) per the datasheet typical application: 470 nF on MICBIAS, CT and BIAS, 2.2 µF on CG, 1 µF + 100 nF on VDD. SHDN and TH to 3V3; A/R strapped to GND (attack:release 1:500 — fast release suits trigger use).
Gain strap JP1 (3-pad solder jumper): 1-2 bridged = 50 dB (default), 2-3 = 40 dB, both open = 60 dB.
LMV7219M5 comparator: +in is the 1 µF AC-coupled amp output biased to half-rail by 2 × 100 kΩ; −in is the wiper of Bourns TC33X 10 kΩ trimmer RV1. Push-pull output, no pull-up needed.
Module-driven SOUND and SOUND_RAW pass 100 Ω series resistors.

PMOD pin	1	2	3	4	5	6	7	8	9	10	11	12
Net	SOUND	SOUND_RAW	NC	NC	GND	3V3	NC	NC	NC	NC	GND	3V3

Regenerate#

python3 generate_design.py

Remaining for release#

[ ] PCB layout, DRC, fab outputs
[ ] hdl/: edge detector + pulse stretcher, ECP5 demo
[ ] BOM export and availability check, design-review checklist