TriggerBox

Programmable MIMO synchronization device: software and hardware design

Input

• Active Triggers (source): Reads TTL signal rising edge (5V) from the TriggerBox system. Intended to coordinate with a manually conducted push-trigger.
• Passive Triggers (sink): Reads TTL signal rising edge (5V) from other systems, current rated to 20mA (e.g., a trigger signal from a motion controller or high-speed camera).

Output

• Flash: A driving pulse to a standard LED diode
• Beep: Drives a buzzer with a specific tone
• Trigger Signal: Sends a TTL signal to other systems, 5V 20mA or amplified with an LM386 amplifier
• Gate: Stays high when the system is armed, low when disarmed

Logic

V2.6: General-purpose version

• The system reads a trigger input signal, either manual or motion pulse
• The system gets armed
• Flashes and beeps with a programmed pattern
• Trigger output is sent simultaneously; gate remains high
• Another trigger input disarms the system with a flash, beep, and trigger output

V3.01: New features for PIV/Laser system

• Takes inputs from the safety curtain and PTUX to control the gate of the DM laser
• Armed by push trigger
• Opens the laser gate only if the system is armed and LaVision is ready (PTU output HIGH)
• The system is disarmed by pressing the manual trigger again or if an object falls through the safety curtain

Software

• TriggerBox: Arduino code to drive the box
• TriggerFinder: {rising, falling} = TriggerFinder(High, Low, State)
  • MATLAB function for post-processing the trigger signal
  • Digitizes: sets any value below Low to 0 and any value above High to 5
  • Derivative used to find peaks at rising and falling edges
• BeepFinder
  • Detects beep tones collected by a microphone in post-processing
  • Uses Short-Time Fourier Transform (STFT) to visualize time history of the spectrum
  • Uses cross-correlation to find beep patterns on the STFT
• InlineTrigger
  • Generates a burst of pulses upon receiving one TTL pulse

Hardware

The listed hardware has been verified to be compatible. Alternatives may also be used since these are standard components.

• Arduino (Nano, Uno for legacy versions)
• Shield board: see PCB design
• 3–24V buzzer, for example — loud enough :)
• LED diode — very bright...
• LM386 Amplifiers
• LED driver

PCB Design

• The shield board is customized for hardware interface
• The design files are provided in the PCB design .zip archive
• We chose JLCPCB as our manufacturer