Ryan Malloy
86a5db5b08
Rewire GPIO↔HMC472A so GPIO(n) = step bit (n-1): GPIO1→V6(0.5dB), GPIO2→V5(1dB), ... GPIO6→V1(16dB) This enables single-instruction GPIO updates: GPIO.out_w1tc = (step & 0x3F) << 1 GPIO.out_w1ts = (~step) & 0x7E Replaces 28-line loop with 4-line bitwise code.
128 lines
5.6 KiB
Markdown
128 lines
5.6 KiB
Markdown
# HMC472A Attenuator Controller Wiring
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## Connection Diagram
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## Pin Mapping (Optimized for Bitwise Ops)
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The wiring is arranged so GPIO number = step bit position + 1, enabling single-instruction bitwise operations in firmware.
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| ESP32-S2 Mini | HMC472A Module | Step Bit | Attenuation |
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|---------------|----------------|----------|-------------|
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| GPIO1 | V6 | Bit 0 (LSB) | 0.5 dB |
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| GPIO2 | V5 | Bit 1 | 1 dB |
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| GPIO3 | V4 | Bit 2 | 2 dB |
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| GPIO4 | V3 | Bit 3 | 4 dB |
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| GPIO5 | V2 | Bit 4 | 8 dB |
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| GPIO6 | V1 | Bit 5 (MSB) | 16 dB |
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| 5V (VBUS) | +5V | — | Power |
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| GND | GND | — | Ground |
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### Why This Mapping?
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```c
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// Old approach (loop required):
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for (int i = 0; i < 6; i++) {
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pin = ATTEN_PINS[5-i]; // Reverse mapping
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if (step & (1 << i)) set_low(pin);
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}
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// New approach (pure bitwise):
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GPIO.out_w1tc = (step & 0x3F) << 1; // Set LOW where step=1
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GPIO.out_w1ts = (~step & 0x3F) << 1 & 0x7E; // Set HIGH where step=0
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```
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The step value bits map directly to GPIO register positions. No loop, no lookup table.
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## HMC472A Module Header Pinout
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The 8-pin header on the HMC472A module (top to bottom when viewing from component side):
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| Pin | Signal | ESP32 GPIO | Description |
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|-----|----------|------------|--------------------------|
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| 1 | +5V | 5V VBUS | Power supply (+5V DC) |
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| 2 | V6 | GPIO1 | 0.5 dB (step bit 0, LSB) |
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| 3 | V5 | GPIO2 | 1 dB (step bit 1) |
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| 4 | V4 | GPIO3 | 2 dB (step bit 2) |
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| 5 | V3 | GPIO4 | 4 dB (step bit 3) |
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| 6 | V2 | GPIO5 | 8 dB (step bit 4) |
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| 7 | V1 | GPIO6 | 16 dB (step bit 5, MSB) |
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| 8 | GND | GND | Ground |
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## Logic Levels
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**Active-LOW control:**
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- **LOW (0V)** = Attenuate (apply the dB value)
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- **HIGH (3.3V or 5V)** = Pass (0 dB contribution)
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The HMC472A accepts 0–5V TTL/CMOS logic. The ESP32-S2's 3.3V GPIO output is fully compatible.
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## Attenuation Examples
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| Step | Binary | GPIO State (1-6) | Total Attenuation |
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|------|------------|------------------|-------------------|
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| 0 | `0b000000` | `HHHHHH` | 0 dB |
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| 1 | `0b000001` | `LHHHHH` | 0.5 dB |
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| 5 | `0b000101` | `LHLHHH` | 2.5 dB |
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| 31 | `0b011111` | `LLLLLH` | 15.5 dB |
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| 63 | `0b111111` | `LLLLLL` | 31.5 dB |
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Formula: `attenuation = step × 0.5 dB` where step = 0–63
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## Wiring Diagram (Text)
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```
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ESP32-S2 Mini HMC472A Module
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(Left Header) (8-pin Header)
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3V3 ─┤ 1 ┌─────┐
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──────────────────────────────┐ │ +5V │← 1
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GPIO1 ─┤ 2 ───────────────────│ V6 │← 2 (0.5 dB)
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GPIO2 ─┤ 3 ───────────────────│ V5 │← 3 (1 dB)
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GPIO3 ─┤ 4 ───────────────────│ V4 │← 4 (2 dB)
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GPIO4 ─┤ 5 ───────────────────│ V3 │← 5 (4 dB)
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GPIO5 ─┤ 6 ───────────────────│ V2 │← 6 (8 dB)
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GPIO6 ─┤ 7 ───────────────────│ V1 │← 7 (16 dB)
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GND ─┤ 8 ───────────────────│ GND │← 8
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└─────┘
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(Right Header)
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5V ─┤ 16 ─────────────────┘ (to +5V)
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```
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**Note:** The diagram shows straight-through wiring (no crossovers) because the optimized mapping aligns GPIO numbers with the module header in reverse order.
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## ESP32-S2 Mini Physical Pinout
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```
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┌─────────────────┐
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│ USB-C │
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└─────────────────┘
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3V3 ─┤ 1 16 ├─ 5V (VBUS) ──► +5V
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GPIO1 ─┤ 2 15 ├─ GPIO15 (LED) │
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GPIO2 ─┤ 3 14 ├─ GPIO14 │
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GPIO3 ─┤ 4 13 ├─ GPIO13 │
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GPIO4 ─┤ 5 12 ├─ GPIO12 │
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GPIO5 ─┤ 6 11 ├─ GPIO11 │
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GPIO6 ─┤ 7 10 ├─ GPIO10 │
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GND ─┤ 8 9 ├─ GPIO9 │
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└─────────────────┘ │
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↓ ↓ ↓ ↓ ↓ ↓ │
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V6 V5 V4 V3 V2 V1 ◄───────────┘
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(HMC472A control pins + power)
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```
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GPIOs 1–6 are on the left header, pins 2–7. Direct ribbon cable from S2 Mini left header to HMC472A control header (reversed).
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## KiCad Schematic
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A full KiCad schematic is available at `hmc472-controller.kicad_sch` for detailed EDA work.
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## Notes
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1. **No level shifting required** — ESP32-S2 3.3V GPIO drives HMC472A directly
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2. **Boot state** — GPIOs default HIGH at boot = 0 dB attenuation (safe)
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3. **Glitch-free switching** — Firmware uses register-level writes (`GPIO.out_w1ts`/`GPIO.out_w1tc`)
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4. **Power** — The S2 Mini's 5V pin sources USB VBUS directly, sufficient for HMC472A's 2.5 mA draw
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5. **Bitwise optimization** — GPIO = bit + 1 mapping eliminates loop in firmware
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