Portable Bluetooth Hotkey Button

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1. 01

   Prepare the enclosure and button

   Make the mounting hole required by your chosen large red normally-open arcade button (24 mm for the selected catalog style). Fit the button and tighten its retaining nut; keep the switch terminals and LED terminals identifiable.

   • Tip: Choose a red button whose LED section is rated for 3.3 V or has an internal resistor.
   • Tip: Use an enclosure that cannot let the battery terminals or power-board solder joints touch metal.

   • ⚠ Do not use a latching on/off switch as the hotkey button; it must be a momentary, normally-open switch.
2. 02

   Wire the button

   Connect button SW1 to ESP32 GPIO27 and SW2 to an ESP32 GND pin. Connect LED+ to GPIO13 and LED- to ESP32 GND. The firmware uses GPIO27’s internal pull-up, so no extra switch resistor is needed.

   • Tip: Keep these wires short and strain-relieved.
   • Tip: GPIO13 turns the button light on only after the PC has connected over Bluetooth.

   • ⚠ Do not connect the switch contact to 3.3 V; it is wired between GPIO27 and ground.
3. 03

   Build the protected battery and regulator chain

   Install a protected 18650 cell in its holder. Connect battery +V to charger B+ and battery GND to charger B-. Connect charger OUT+ to regulator VIN and charger OUT- to regulator GND. Set the regulator output to exactly 3.3 V with a multimeter before connecting the ESP32.

   • Tip: Use the charger module’s protected OUT+/OUT- terminals for the load, not B+/B-.
   • Tip: A 2500 mAh cell is estimated at roughly 16 hours of active use; actual time depends heavily on Bluetooth connection activity and regulator efficiency.

   • ⚠ Never short, puncture, reverse, or charge an 18650 cell without protection.
   • ⚠ Do not connect the 4.2 V battery/charger output directly to the ESP32 3V3 pin.
   • ⚠ Use only the TP4056 module’s 5 V USB input for charging.
4. 04

   Power the ESP32

   Connect regulator VOUT to the ESP32 3V3 pin. Ensure regulator GND, charger OUT-, and the ESP32 GND pins are all common ground. Mount and insulate the boards so they cannot short against the enclosure or battery holder.

   • Tip: Verify 3.3 V again between ESP32 3V3 and GND before installing the ESP32.
   • Tip: Use a separate accessible USB opening for the TP4056 charging connector.

   • ⚠ Do not feed the regulator’s 3.3 V output into ESP32 VIN/5V.
   • ⚠ Disconnect battery power before changing wiring.

#include <Arduino.h>
#include <BleKeyboard.h>


// Forward declarations
void sendHotkey();

constexpr uint8_t BUTTON_PIN = 27;
constexpr uint8_t BUTTON_LED_PIN = 13;
constexpr uint32_t DEBOUNCE_MS = 35;
constexpr uint32_t KEY_HOLD_MS = 40;

BleKeyboard bleKeyboard("Emergency Hotkey Button", "Schematik", 100);

bool rawLast = HIGH;
bool stableState = HIGH;
uint32_t rawChangedAt = 0;

void sendHotkey() {
  if (!bleKeyboard.isConnected()) {
    return;
  }

  bleKeyboard.press(KEY_LEFT_CTRL);
  bleKeyboard.press(KEY_LEFT_ALT);
  bleKeyboard.press(KEY_F9);
  delay(KEY_HOLD_MS);
  bleKeyboard.releaseAll();
}

void setup() {
  pinMode(BUTTON_PIN, INPUT_PULLUP);
  pinMode(BUTTON_LED_PIN, OUTPUT);
  digitalWrite(BUTTON_LED_PIN, LOW);
  bleKeyboard.begin();
}

void loop() {
  const bool connected = bleKeyboard.isConnected();
  digitalWrite(BUTTON_LED_PIN, connected ? HIGH : LOW);

  const bool rawNow = digitalRead(BUTTON_PIN);
  const uint32_t now = millis();

  if (rawNow != rawLast) {
    rawLast = rawNow;
    rawChangedAt = now;
  }

  if ((now - rawChangedAt) >= DEBOUNCE_MS && rawNow != stableState) {
    stableState = rawNow;
    if (stableState == LOW) {
      sendHotkey();
    }
  }

  delay(2);
}

“Deploy to device” opens this project in Schematik, where you can flash it to your board over USB.