Invisible Touch Alarm System for Doors

Step 1: Prepare the TTP223 Touch Sensor

• Identify the 3 pins on the TTP223: OUT (1st), VCC (2nd), and GND (3rd)
• Gently bend the 1st pin (OUT) and 3rd pin (GND) outward for easy connection
• Keep the 2nd pin (VCC) straight for connecting to battery positive
• Cut the extra length of the bent pins using a wire cutter
• Connect the 3rd pin (GND) of TTP223 directly to the Source pin of the IRFZ44N MOSFET
• Ensure no pins are touching each other after bending

Step 2: Connect Push Switch and 220Ω Resistor

• Take the push-on switch (2 legs)
• Solder one leg of the switch to the 1st pin (Gate) of the IRFZ44N MOSFET
• Take a 220Ω resistor
• Solder one side of the resistor to the same 1st pin (Gate) of the IRFZ44N

Step 3: Complete Optocoupler Input Connections

• Cut the excess legs of the PC817 optocoupler to keep the layout compact
• Connect the 1st leg (anode) of PC817 to the free side of the 220Ω resistor (the same resistor connected to IRFZ44N Gate)
• Connect the 2nd leg (cathode) of PC817 to the VCC pin of the TTP223 touch sensor

Step 4: Connect Second 220Ω Resistor

• Take another 220Ω resistor
• Solder one end of the resistor to the 1st pin (VCC) of the TTP223 touch sensor
• Solder the other end of the resistor to the 4th pin of the PC817 optocoupler

Step 5: Mount Circuit and Final Soldering

• Take a 3mm acrylic sheet — this will be the base for your circuit
• Place all components neatly and glue them onto the acrylic sheet
• Use thick copper wire to make strong solder bridges between components
• Solder the 1st leg (Gate) of the IRFZ44N MOSFET to the 3rd pin of the PC817 optocoupler

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Step 7: Connect Power Supply and Finish Mounting

• Take another piece of thick copper wire
• Connect it from the GND line of the circuit to the GND terminal of the 18650 battery holder
• Glue the 18650 battery holder onto the acrylic sheet securely
• Solder the VCC pin (1st leg) of the TTP223 to the positive terminal of the 18650 holder

Step 8: Connect the Buzzer

• Take a 3V to 12V DC buzzer
• Glue it onto any free space on the acrylic sheet
• Solder the negative (–) leg of the buzzer to the center pin (Drain) of the IRFZ44N MOSFET
• Solder the positive (+) leg of the buzzer to the VCC pin (1st pin) of the TTP223 touch sensor

Step 9: Touch Pad Setup and Final Assembly

• Gently scratch the copper pad area of the TTP223 sensor to expose clean metal
• Solder a single wire to this pad — this will act as the external touch contact (can be attached to a door handle or metal plate)
• After confirming all wiring is done, take 4 pieces of acrylic sheet to cover all sides of the project
• Glue all edges securely to fully enclose and protect the circuit
• Optionally, seal all open points with a small amount of hot glue for durability and insulation

Step 10: Power Up and Test the Circuit

• Insert a fully charged 18650 battery into the battery holder
• Once powered, your circuit is active and ready to use
• Touch the wire connected to the TTP223 sensor — the buzzer should turn ON immediately
• Now press the push-button switch — this will reset the system and turn OFF the buzzer

Step 11: Mount the System on Door

• Fix the completed acrylic unit near the door handle, using screws or strong double-sided tape
• Take the touch wire (connected to the TTP223 sensor) and attach it securely to the metal handle or handle frame
• Make sure the exposed wire touches or wraps around part of the handle where a person would normally place their hand
• This setup allows the system to detect touch even through gloves, thanks to the capacitive sensing of the TTP223
• When someone touches any part of the handle, the buzzer activates immediately
• To turn off/reset the alarm, simply press the push-button switch

Step 12: Real-World Action – Alarm Response

• Once everything is mounted and powered, the system is fully armed
• If a thief touches the door handle, even while wearing gloves, the TTP223 detects the touch
• The alarm buzzer sounds immediately, drawing attention and alerting everyone nearby
• As the theft runs away, the system stays active until someone presses the reset button to turn off the buzzer

✅ Your DIY Touch-Activated Door Alarm System is now fully complete and working as intended!

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