Week 7 - Input Devices Group Assignment Summary

Probing Analog and Digital Signals from Various Input Devices

Assignment Overview

This page summarizes the group assignment for Week 8, focusing on probing input devices' analog levels and digital signals. We systematically investigated load cells, microphones, and IR phototransistors to understand their signal characteristics and measurement techniques.

Group Assignment: Probing Analog and Digital Signals

Three focused investigations: load cell (analog vs amplified digital), digital microphone (16 kHz clocked), and IR phototransistor (analog). Each subsection includes probe setup, scope captures, and brief interpretation.

Signal Analysis Overview

Comprehensive analysis of input device signals to understand analog and digital signal characteristics, measurement techniques, and practical applications in embedded systems.

Reference Materials

Source: MIT HTMAA Week 7 Group Assignment

Detailed documentation of input device signal analysis and measurement techniques

Key Signal Analysis Parameters

  • Load Cell Analysis: Wheatstone bridge differential output vs HX711 amplified digital interface
  • Microphone Signals: 16 kHz clocked digital output with synchronous data capture
  • IR Phototransistor: Analog voltage changes with illumination intensity
  • Signal Processing: Analog-to-digital conversion and signal conditioning techniques
  • Measurement Tools: Oscilloscope operation and probe setup for accurate signal capture
  • Data Interpretation: Understanding signal characteristics and practical applications

Load Cell: Direct Analog Output and HX711 Digital Output

We compare the raw Wheatstone bridge differential output to the HX711-amplified, clocked digital interface.

Why an amplifier board is needed

With a 3.3 V reference, the ADC step size (LSB) is 3.3 V ÷ 2N. Load-cell bridge outputs are only millivolts, so low-resolution ADCs can't resolve changes well.

  • 8-bit ADC (N=8): ~13 mV per LSB (3.3 V ÷ 256)
  • 10-bit ADC (N=10): ~3.2 mV per LSB (3.3 V ÷ 1024)
  • 12-bit ADC (N=12): ~0.8 mV per LSB (3.3 V ÷ 4096)

At minimum, 12-bit ADC is needed to read the raw bridge signal directly on a microcontroller; a dedicated amplifier + ADC (e.g., HX711) increases gain and effective resolution, improving SNR and measurement fidelity.

Load cell Wheatstone bridge with sense leads identified
Load cell Wheatstone bridge with sense leads identified
Millivolt-level differential changes at the bridge confirm expected polarity and sensitivity
Clock (SCK) captured at the HX711 board - SCK amplitude appears low due to probing and wiring; edges align with HX711 data framing and drive DT shifting
Data (DT) line transitions during conversion readout - bit transitions align to SCK, representing the ADC output stream

Microphone: Digital output with 16 kHz clock

We capture the probe points, the ~16 kHz clock, and the synchronous data output.

Microphone probe points
Probe points for clock and data relative to module ground
Microphone clock line at ~16 kHz
~16 kHz clock observed as a clean square wave
The mic's clock provides the sampling reference for synchronous data capture
Microphone digital data output
Digital output edges align to the clock for bit capture - data toggles on defined edges enabling reliable sampling and decoding

IR Phototransistor: Analog output

We power the IR emitter, probe the phototransistor node, and observe analog voltage changes with illumination.

IR phototransistor probe points
Probe across sense node and reference
IR diode power supply setup
IR diode power supply setup
IR diode powered on
The emitter is powered and positioned to control incident IR on the phototransistor for response testing
Analog output changes with IR intensity - increasing light increases conduction, lowering the sensed voltage across the load resistor

Full Assignment Details

For complete details on the Week 7 group assignment, including comprehensive input device signal analysis, measurement techniques, and detailed results, please visit the full assignment page.

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Special Thanks to Our Section

We would like to express our sincere gratitude to all members of our section for their invaluable collaboration throughout this group assignment. Your contributions were essential to the success of this comprehensive input device signal analysis project.

Collaboration Activities
  • Signal measurement and oscilloscope operation
  • Input device testing and characterization
  • Analog and digital signal analysis
  • Measurement technique documentation
Knowledge Sharing
  • Oscilloscope operation and probe setup techniques
  • Signal processing and measurement methodologies
  • Input device characteristics and applications
  • Embedded systems signal analysis

This collaborative effort demonstrates the power of teamwork in technical education and hands-on learning. The collective knowledge and shared experiences significantly enhanced our understanding of input device signal characteristics and measurement techniques.

References

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Week 7 - Input Devices Group Assignment Summary Development

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