Competitive shooting measures time taken over the course of fire (COF). A stop plate is recommended for recording last shot attempted on a COF for airsoft as shots are not loud enough for consistent microphone pickup. Competition grade hardware are often expensive and hard to source. A home brew solution can be a good back up.

• Support commercial off the shelf stop plates or PC microphones strapped to a steel plate(see stop plate section).
• Random 1 to 4 seconds delay of start signal after timer trigger.
  • Required by IPSC rule 8.3.3.

• M5Stack ESP32 Basic Core IoT Development Kit (Other model would likely work as this is Blockly/MicroPython)
  • Timer listens to stop plate signal on ADC

  M5Stack ADC --- LM386 module --- mini plug socket --- stop plate
  

• Using your favorite shooting timer app on mobile phone
  • App with adjustable sensitivty and tune towards dry fire level
  • Build a TRRS plug cable to connect with stop plate and external speaker
  • For phone with USB type C or lightning port, an adptor with TRRS support is required, not all adaptor have TRRS support for microphone

                               TRS plug --- Powered Speaker
                               LRG
                               |||
                 +-------------+||
                 |+-------------+|
                 ||+-------------+
                 |||
                 LRGM                
Mobile Phone --- TRRS plug (in CITA format for Android and iPhone)
                 LRGM
                   ||
                   |+----------+
                   +----------+|
                              ||
                              MG
                              TS socket -- Stop Plate

• Stop Plate using M5Stack Atom Lite

Piezoelectric ------------------------------ DAC0 pin 33 on M5Stack Atom Lite
Speaker               |         
                Resistor 1M Ohm
                      |
Piezoelectirc ------------------------------- GND pin on M5Stack Atom Lite
Speaker GND

Mini Plug +   ------------------------------- ADC0 pin 25 on M5Stack Atom Lite
Mini Plug GND ------------------------------- GND pin on M5stack Atom Lite

• Stop Plate using Raspberry Pi Pico

Piezoelectric ------------------------------ TBD pin on Raspberry Pi Pico
Speaker               |         
                Resistor 1M Ohm
                      |
Piezoelectirc ------------------------------- GND pin on Raspberry Pi Pico
Speaker GND

Mini Plug +   ------------------------------- TBD pin on Raspberry Pi Pico
Mini Plug GND ------------------------------- GND pin on Raspberry Pi Pico

Micro Python built from UIFLow with Blocky, targeting M5Stack devices

• Open uiflow/main.m5f from UIFlow
• Put your M5Stack device under proper mode (e.g. Internet mode or USB mode) for programming
• Hit the "Play" (Right Arrow) button
• logo.png for customized logo
• Time for last 20 stop plate hit is displayed

• Open uiflow/stop_plate_atomlite.m5f from UIFlow
• Put your M5Stack device under proper mode (e.g. Internet mode or USB mode) for programming
• Hit the "Play" (Right Arrow) button

• Use Arudino IDE, open arduino/stopplate/stopplate.ino

• Minimalize global variable, but still unavoidlable in Blockly/MicroPython
  • Globals are accessed by event handlers (e.g. button etc), pretty bad for multithreading but necessary evil the way how Blockly works now. Assuming we don't have this advanced MicroPython enabled yet :)
• NOT IMPLEMENTED, A HINT FOR FUTURE EXPANSION Action camera supporting SJCAM API over Wifi (tested on SJ4000 Wifi) the great guide.

• Basic ESP32 turn out having enough juice with following caveats
  • The countdown screen refresh taken much of CPU load, buttons are less responsive there but we don't care during count down
  • Hence the refresh timer is stopped before start signal beeps to disable the frequent refresh of stopwatch, plus matching behavior of most shot timers out there