Reaction trainer/timer

General overview:

This is a reaction trainer that I made for school work. It's a very simple design and requires minimal hardware. There are some required components like:

-Bambu lab COB LED strip 200mm

-A simple push button (https://www.amazon.co.uk/Gebildet-Prewired-Waterproof-Momentary-Stainless/dp/B08L49F7DV/ref=sr_1_6) I used this one.

-An esp32 controller

-A mosfet (preferably LB8721)

-A couple jumper wires and a 100ohm resistor and a 10k ohm resistor and a breadboard

Assembly instruction:

1.Wire the electronics using either a small breadboard or a prototype PCB board(either are fine).

Button:

GPIO13 ─ Button ─ GND

LED and mosfet:

GPIO27 ──220Ω── Gate
Gate ──10kΩ── GND

5V ─── LED +
LED − ─── Drain
Source ─── GND

2. Upload the code to the ESP32.

const int buttonPin = 13;
const int ledPin = 27;

unsigned long startTime;
unsigned long reactionTime;

// debounce
bool buttonPressed()
{
 if (digitalRead(buttonPin) == LOW)
 {
   delay(20);
   if (digitalRead(buttonPin) == LOW)
     return true;
 }
 return false;
}

// flash LED function
void flashLED(int times, int delayTime)
{
 for(int i = 0; i < times; i++)
 {
   digitalWrite(ledPin, HIGH);
   delay(delayTime);
   digitalWrite(ledPin, LOW);
   delay(delayTime);
 }
}

void setup()
{
 pinMode(buttonPin, INPUT_PULLUP);
 pinMode(ledPin, OUTPUT);

 digitalWrite(ledPin, LOW);

 randomSeed(analogRead(34));
}

void loop()
{
 digitalWrite(ledPin, LOW);

 // WAIT FOR START
 while(digitalRead(buttonPin) == HIGH)
 {
 }

 delay(300);

 // wait release
 while(digitalRead(buttonPin) == LOW)
 {
 }

 // RANDOM WAIT
 unsigned long waitTime = random(2000,5000);
 unsigned long timerStart = millis();

 while(millis() - timerStart < waitTime)
 {
   if(buttonPressed())
   {
     // FALSE START → rapid flashing
     flashLED(10, 100);
     return;
   }
 }

 // GO SIGNAL
 digitalWrite(ledPin, HIGH);

 startTime = millis();

 while(digitalRead(buttonPin) == HIGH)
 {
 }

 reactionTime = millis() - startTime;

 digitalWrite(ledPin, LOW);

 delay(500);

 // SHOW RESULT USING FLASHES
 // convert ms → number of flashes (scaled)
 int flashes = reactionTime / 50;

 if(flashes > 20) flashes = 20; // limit

 flashLED(flashes, 150);

 delay(2000);
}

3. Assemble the reaction trainer.

Put all the 4 sides onto the pressing mechanism and screw the button into the circular cut out on the pressing mechanism.

Plug in the esp32 into a usb c cable and have fun training/timing your reaction speed.