# HMC472A Attenuator Controller Wiring

## Connection Diagram

![Wiring Diagram](wiring-diagram.svg)

## 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

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