Update design and testing documentation; add sensor details and improve clarity

Author: AdzCoder

docs/DESIGN.md

@@ -1,3 +1,14 @@
+# Design Documentation
+
+## System Overview
+
+The system was designed to collect flight data from a water rocket including:
+
+- Atmospheric pressure changes during ascent/descent
+- Triaxial acceleration data
+- Temperature changes
+- Calculated altitude
+
 ## Design Requirements
 
 - Sampling rate: 10 Hz (100ms intervals)
@@ -10,7 +21,7 @@
 
 ### Module Structure
 
-- `main.cpp`: System initialization and main control loop
+- `main.cpp`: System initialisation and main control loop
 - `sensors.cpp/h`: Sensor data acquisition and processing
 - `data_logger.cpp/h`: SD card file operations
 - `config.h`: Pin definitions, calibration constants, system parameters
@@ -55,4 +66,41 @@ Uses barometric formula: h = 44330 × (1 - (P/P₀)^(1/5.257))
 
 ## Components
 
-[Keep existing Components section]
+### Sensors
+
+- **Accelerometer**: DFRobot WT61PC 6-axis IMU
+  - Measures acceleration and angular velocity
+  - Output frequency configurable up to 200Hz
+- **Pressure Sensor**: MPX4115A
+  - Measures 15-115 kPa absolute pressure
+  - Used to calculate altitude changes
+- **Temperature Sensor**: LM35DT
+  - Measures -55°C to +150°C range
+  - Linear 10mV/°C output
+
+### Data Storage
+
+- MicroSD card breakout board
+- FAT32 formatted SD card
+
+### Indicators
+
+- Piezo buzzer (85-96dB) for recovery
+- Red LED panel light for power status
+
+## Circuit Design
+
+![Circuit Plan](circuit_plan.png)
+
+Power:
+
+- 9V battery
+- Arduino Micro voltage regulation
+
+Connections:
+
+- Accelerometer: SoftwareSerial on pins 10(RX), 11(TX)
+- Pressure Sensor: Analogue A2
+- Temperature Sensor: Analogue A3
+- SD Card: SPI on pin 17(CS)
+- Buzzer: Digital 13

docs/TESTING.md

@@ -128,7 +128,7 @@
    - Workaround: Use pressure sensor temperature compensation
    - Future fix: Relocate sensor away from high-frequency digital lines
 
-2. **SD Card Initialization Delay**
+2. **SD Card Initialisation Delay**
    - Impact: 2-3 second startup delay
    - Mitigation: Acceptable for pre-launch preparation time