hmc472/hardware/wiring.md

HMC472A Attenuator Controller Wiring

Connection Diagram

Pin Mapping (Optimized for Bitwise Ops)

The wiring is arranged so GPIO number = step bit position + 1, enabling single-instruction bitwise operations in firmware.

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

Why This Mapping?

// Old approach (loop required):
for (int i = 0; i < 6; i++) {
    pin = ATTEN_PINS[5-i];  // Reverse mapping
    if (step & (1 << i)) set_low(pin);
}

// New approach (pure bitwise):
GPIO.out_w1tc = (step & 0x3F) << 1;           // Set LOW where step=1
GPIO.out_w1ts = (~step & 0x3F) << 1 & 0x7E;   // Set HIGH where step=0

The step value bits map directly to GPIO register positions. No loop, no lookup table.

HMC472A Module Header Pinout

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

Pin	Signal	ESP32 GPIO	Description
1	+5V	5V VBUS	Power supply (+5V DC)
2	V6	GPIO1	0.5 dB (step bit 0, LSB)
3	V5	GPIO2	1 dB (step bit 1)
4	V4	GPIO3	2 dB (step bit 2)
5	V3	GPIO4	4 dB (step bit 3)
6	V2	GPIO5	8 dB (step bit 4)
7	V1	GPIO6	16 dB (step bit 5, MSB)
8	GND	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

Step	Binary	GPIO State (1-6)	Total Attenuation
0	0b000000	HHHHHH	0 dB
1	0b000001	LHHHHH	0.5 dB
5	0b000101	LHLHHH	2.5 dB
31	0b011111	LLLLLH	15.5 dB
63	0b111111	LLLLLL	31.5 dB

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

Wiring Diagram (Text)

ESP32-S2 Mini                    HMC472A Module
   (Left Header)                   (8-pin Header)

        3V3 ─┤ 1                   ┌─────┐
   ──────────────────────────────┐ │ +5V │← 1
     GPIO1 ─┤ 2 ───────────────────│ V6  │← 2  (0.5 dB)
     GPIO2 ─┤ 3 ───────────────────│ V5  │← 3  (1 dB)
     GPIO3 ─┤ 4 ───────────────────│ V4  │← 4  (2 dB)
     GPIO4 ─┤ 5 ───────────────────│ V3  │← 5  (4 dB)
     GPIO5 ─┤ 6 ───────────────────│ V2  │← 6  (8 dB)
     GPIO6 ─┤ 7 ───────────────────│ V1  │← 7  (16 dB)
        GND ─┤ 8 ───────────────────│ GND │← 8
                                   └─────┘
   (Right Header)
         5V ─┤ 16 ─────────────────┘ (to +5V)

Note: The diagram shows straight-through wiring (no crossovers) because the optimized mapping aligns GPIO numbers with the module header in reverse order.

ESP32-S2 Mini Physical Pinout

          ┌─────────────────┐
          │     USB-C       │
          └─────────────────┘
     3V3 ─┤ 1            16 ├─ 5V (VBUS) ──► +5V
  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          │
          └─────────────────┘                 │
            ↓   ↓   ↓   ↓   ↓   ↓             │
           V6  V5  V4  V3  V2  V1 ◄───────────┘
           (HMC472A control pins + power)

GPIOs 1–6 are on the left header, pins 2–7. Direct ribbon cable from S2 Mini left header to HMC472A control header (reversed).

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)
4. Power — The S2 Mini's 5V pin sources USB VBUS directly, sufficient for HMC472A's 2.5 mA draw
5. Bitwise optimization — GPIO = bit + 1 mapping eliminates loop in firmware