Radu: Measuring the Speed of Light
Radu: Measuring the Speed of Light in a 6x1 setup.
info
Author: Sainenco Luchian (1221C)
GitHub Project Link: https://github.com/UPB-PMRust-Students/project-LucaSain
Description
In 1850s Fizeau measured the speed of light in a 8km setup using a gear. The key point of the measurement was that the light would travel the distance from the source and back slower than the aperture of the gear. Today, using high reflectivty mirrors, electrical motors and high precision laser cutting we can repeat Fizeau in a 3x1m setup.
Project Development Blog: LucaSain's Blog
Motivation
I went to ELI-NP Winter school and I enojyed the labs we had there so I decided to build my own "lab application" to measure the speed of light just like Fizeau did in 1850 but using modern technologies.
Architecture
Main Functionality
- 200mW 640nm Laser releases a beam
- The beam passes through the aperture of an aluminium disk
- The aluminium disk is rotating at about 7000rpm by an electrical engine (calibrated using PID)
- Next the beam reflects off a setup of high reflectivity mirrors
- Using a final mirror, the beam is reflected back the path and through the aperture
- A diode detects the intensity of the laser beam and is used to sample a signal
- By analysing the discrete signal the speed of light can be computed
We distinguish three main components:
- Control panel (interface)
- Control systems
- Motor control (PID)
- Optics control
More about these in the hardware part
Log
Week 5 - 11 May
- Tested the LLM capabiltiy and changed the project theme.
- Theoretical setup and architecture for the actual project.
Week 12 - 18 May
- Tested the disc with a VFD. Won the the first place at SCSS FILS ETTI with the experimental setup.
- Tried to build a AC driver circuit for the motors.
- Found a decent DC motor and driver (thanks to RoboBadgers). Will replace the second PID laser sensor with a Hall sensor.
- 3D design the case for the dashboard. (tbd by Tuesday)
- 3D design holders for the small calibrating mirrors. (tbd by Monday)
- Print the hardware to integrate the DC motor into the Grinder case.
- Ordered a new laser because the old one burned during the experimental setup.
- Designed holders for the high reflectivity mirrors.
- Add pictures with the Diode Amp Circuit. (tbd on Monday)
- Add pictures with the mirror setup. (tbd on Monday)
Week 19 - 25 May
- Setup the Motor Control via PID by Tuesday
- Setup the Laser Optics Setup by Tuesday
- Setup the Signal Capturing using the esp32 by Wednesday
- Build the Dashboard by Friday
- Wireless connectivity by Sunday (ESP-NOW and WiFi)
- MQTT data transfer by Sunday
Hardware
The hardware will be built around three chips made by espressiff.
Control Panel Component
This is the control panel for the whole setup.
- Two 4 digit common anode display will be used to display the measured and the theoretical RPM for the motor.
- One potentiometer will be used to manipulate the speed of the motor.
- Two potentiometers will control the calibrating mirrors.
- One pair of switch + button (+ led for status) will arm and control the power status of the motor.
- Another pair (+ led for status) will arm and control the power status of the laser.
- The LCD display will show the signal captured through the diode.
- Everything driven by the ESP32-Wroom.
This is the Motor System.
- A high power H-bridge will drive the motor
A power supply is needed (aluminium disk at 7000 rpm will eat some juice)A grinder can be powered directly by AC. A dimmer circuit is needed- I no longer have a VFD. Tried to build my own VFD, the bought IC was broken. Ordered a dimmer circuit with pwm control and got a good DC motor.
A small power laser and diode detector will be used to measure the real speed of the motorA Hall sensor can be used here for more accuracy.- A closed loop is thus created, making PID control possible.
- Everything driven by the ESP32-S2.
This is the Optics Control System.
- A Class 3B (250mW) laser is used as a beam source (a class 3 B laser is dangerous. Wear protecting glasses when it's running).
- Stationary high reflectivity mirrors (about 98% reflected intensity) will reflect the ray back and forth
- Mobile high reflectivity mirrors will be used to focus the beam back into the aperture (calibration will be done manually).
- Diode detector will be used to focus the beam onto the detector diode.
- Everything driven by the ESP32-Wroom
Schematics
Bill of Materials
| Device | Usage | Price |
|---|---|---|
| ESP32-WROOM (x2) | Controllers | 36RON |
| ESP32-S2 | Controllers | 13.07RON |
| High Reflectivity Mirrors | Mirros for increased optical path | 90.25RON |
| Class 3B laser | Laser ray | 68RON |
| 4 Digit LED Common Anode (x2) | Display the measured and theoretical speed of the motor | 3.95RON |
| Push button with hold | Start/stop the laser/motor | 2.77RON |
| ON/OFF Switch | Arm/Disarm the laser/motor | 1.99RON |
| Relay module | Arm/Disarm the motor power supply | 7.99RON |
| SG90 Servo (x4) | Manipulate the calibration mirrors | 12RON |
| Potentiometers (x5) | Set the speed of motor/manipulate the mirrors calibration | 1.49RON |
| Red laser module | Motor Speed Measurement | 2.99RON |
| Photodiodes (x2) | Motor Speed Measurement and Sampling of the signal | ??? Searching for this |
| High Power H-Bridge | Motor Control | 99RON |
| DC 7000 rpm motor/(or Makita Grinder) | Rotation of the aluminium disk | sponsored by RoboBadgers |
| Aluminium disk | Rotation of apertures | Free, Recycled |
| 5V DC Power Supply | Class 3B Laser Power Supply | Free, Recycled |
| Motor Driver | Motor Speed PWM control | sponsored by RoboBadgers |
| Red LED (x2) | Motor and laser status | Free, Recycled |
Software
| sofware | purpose | documentation |
|---|---|---|
| esp-idf-hal/esp-hal | esp32 based-devices hal | documentation |
| pid | pid control for motor rpm | documentation |
| esp-wifi/esp-wifi-sys | wifi and esp-now bindings | documentation |
| minimq | mqtt library | documentation |
Links
Inspiration
Extra References