Ryan Malloy b5794c5f8d Add hardware wiring documentation and KiCad schematic

- wiring.md: Pin mapping table, module pinout, logic levels
- wiring-diagram.svg: Visual connection diagram (S2 Mini ↔ HMC472A)
- hmc472-controller.kicad_pro/sch: KiCad project for EDA work

GPIO1-6 → V1-V6 (active-low, 16/8/4/2/1/0.5 dB)
5V VBUS → +5V, GND → GND

2026-02-03 00:04:56 -07:00

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HMC472A Attenuator Controller Wiring

Connection Diagram

Pin Mapping Table

ESP32-S2 Mini	HMC472A Module	Function	Attenuation
GPIO1	V1	Bit 5 (MSB)	16 dB
GPIO2	V2	Bit 4	8 dB
GPIO3	V3	Bit 3	4 dB
GPIO4	V4	Bit 2	2 dB
GPIO5	V5	Bit 1	1 dB
GPIO6	V6	Bit 0 (LSB)	0.5 dB
5V (VBUS)	+5V	Power	—
GND	GND	Ground	—

HMC472A Module Header Pinout

The 8-pin header on the HMC472A module (top to bottom when viewing from component side):

Pin	Signal	Description
1	+5V	Power supply (+5V DC)
2	V6	0.5 dB control (active-low)
3	V5	1 dB control (active-low)
4	V4	2 dB control (active-low)
5	V3	4 dB control (active-low)
6	V2	8 dB control (active-low)
7	V1	16 dB control (active-low)
8	GND	Ground

Logic Levels

Active-LOW control:

LOW (0V) = Attenuate (apply the dB value)
HIGH (3.3V or 5V) = Pass (0 dB contribution)

The HMC472A accepts 0–5V TTL/CMOS logic. The ESP32-S2's 3.3V GPIO output is fully compatible.

Attenuation Examples

GPIO State (1-6)	Step	Total Attenuation
`111111` (all HIGH)	0	0 dB (insertion loss only)
`111110`	1	0.5 dB
`111100`	3	1.5 dB
`110000`	15	7.5 dB
`100000`	31	15.5 dB
`000000` (all LOW)	63	31.5 dB

Formula: attenuation = step × 0.5 dB where step = 0–63

ESP32-S2 Mini Physical Pinout

          ┌─────────────────┐
          │     USB-C       │
          └─────────────────┘
     3V3 ─┤ 1            16 ├─ 5V (VBUS) ◄── Power to HMC472A
  GPIO1 ─┤ 2            15 ├─ GPIO15 (LED)
  GPIO2 ─┤ 3            14 ├─ GPIO14
  GPIO3 ─┤ 4            13 ├─ GPIO13
  GPIO4 ─┤ 5            12 ├─ GPIO12
  GPIO5 ─┤ 6            11 ├─ GPIO11
  GPIO6 ─┤ 7            10 ├─ GPIO10
     GND ─┤ 8             9 ├─ GPIO9
          └─────────────────┘
            (Left header)

GPIOs 1–6 are on the left header, pins 2–7. Convenient sequential layout for ribbon cable.

KiCad Schematic

A full KiCad schematic is available at hmc472-controller.kicad_sch for detailed EDA work.

Notes

No level shifting required — ESP32-S2 3.3V GPIO drives HMC472A directly
Boot state — GPIOs default HIGH at boot = 0 dB attenuation (safe)
Glitch-free switching — Firmware uses register-level writes (GPIO.out_w1ts/GPIO.out_w1tc) to change all 6 bits atomically
Power — The S2 Mini's 5V pin sources USB VBUS directly, sufficient for HMC472A's 2.5 mA draw

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