florian.berthold
d103b2732c
- BOM with LCSC part numbers for PCBWay assembly - Hand-solder module sources (RP2040-Zero, OLED) - Design doc with block diagram, specs, GPIO pinout - Panel layout concept for 6 HP
136 lines
4.1 KiB
Markdown
136 lines
4.1 KiB
Markdown
# SN-L00 Design Document
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## Overview
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The SN-L00 is a 6 HP Eurorack module that measures round-trip latency in audio/CV signal chains.
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## Block Diagram
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```
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+12V ──┬── LDO ──── 3.3V ──── RP2040-Zero ──── OLED Display
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│ │ │
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│ │ └── I2C (SDA/SCL)
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│ │
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GND ───┴──────────────────────────┤
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│
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┌───────────────────┼───────────────────┐
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│ │ │
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TRIG OUT RETURN IN BUTTON
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│ │ │
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74LVC1G17 MCP6001 Tactile
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(buffer) (buffer) switch
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│ │
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▼ ▼
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3.5mm Jack 3.5mm Jack
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```
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## Signal Flow
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### Trigger Output
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1. RP2040 GPIO generates 5ms pulse (configurable)
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2. 74LVC1G17 Schmitt buffer cleans edge, provides drive strength
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3. Output: 0-3.3V trigger compatible with Eurorack gate inputs
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### Return Input
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1. Eurorack signal (0-5V typical, can be ±5V audio)
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2. Protection diodes clamp to 3.3V rail
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3. MCP6001 op-amp buffers signal
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4. Voltage divider if needed for >3.3V signals
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5. RP2040 GPIO reads with internal Schmitt trigger
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### Measurement
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1. RP2040 starts timer on trigger output rising edge
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2. Timer stops on return input rising edge
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3. Latency = timer count × timer resolution
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4. Display updates with result in ms
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## Specifications
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| Parameter | Value |
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|-----------|-------|
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| Width | 6 HP (30.00mm) |
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| Depth | <25mm (skiff-friendly) |
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| Power +12V | ~20mA |
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| Power -12V | 0mA (not used) |
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| Trigger output | 0-3.3V, 5ms default |
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| Input threshold | ~1.5V (adjustable in firmware) |
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| Resolution | <10μs (RP2040 @ 125MHz) |
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| Range | 0.01ms - 999ms |
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| Display | 128x32 OLED, I2C |
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## Operating Modes
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### Mode 1: Single Shot
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- Press button to trigger measurement
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- Display shows result until next measurement
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- LED blinks on trigger
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### Mode 2: Continuous
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- Hold button 2s to enter continuous mode
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- Triggers every 500ms, displays live reading
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- Shows min/max/average
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- Press button to exit
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### Mode 3: Statistics
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- After measurements, short press cycles through:
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- Last reading
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- Minimum
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- Maximum
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- Average (last 10)
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## Panel Layout (6 HP)
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```
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┌─────────────────────┐
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│ SN-L00 │
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│ │
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│ ┌───────────┐ │
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│ │ OLED │ │
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│ │ 12.4 ms │ │
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│ └───────────┘ │
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│ │
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│ [BTN] │
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│ │
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│ ○ OUT ○ IN │
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│ TRIG RETURN │
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│ │
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│ ● PWR │
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└─────────────────────┘
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```
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## Firmware Architecture
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```
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main.c
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├── init_gpio() # Configure pins
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├── init_i2c() # OLED communication
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├── init_timer() # High-resolution timer
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│
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├── trigger_pulse() # Generate output pulse
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├── wait_for_return() # Monitor input with timeout
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├── calculate_latency() # Timer math
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│
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├── display_update() # OLED rendering
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├── button_handler() # Mode switching
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└── main_loop() # State machine
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```
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## GPIO Assignments (RP2040-Zero)
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| GPIO | Function | Notes |
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|------|----------|-------|
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| GP0 | I2C SDA | OLED |
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| GP1 | I2C SCL | OLED |
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| GP2 | Trigger Out | Via 74LVC1G17 |
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| GP3 | Return In | Via MCP6001 |
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| GP4 | Button | Internal pullup |
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| GP5 | Power LED | Optional |
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## Future Expansion Ideas
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- CV output proportional to latency
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- MIDI output (latency as CC)
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- USB logging to computer
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- Multiple trigger patterns (burst, random)
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- Frequency response mode (sweep test)
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