TTP223 Touch Sensor

The TTP223 is a capacitive touch panel detector integrated circuit (IC) that emulates the functionality of a physical button using capacitive technology. It is designed to replace traditional switches with a more durable solution without moving parts and greater design flexibility. Through a sensitive area (metal pad or PCB), the TTP223 detects human body proximity or contact reliably.

Operating Principle

The sensor works by measuring changes in the capacitance of the environment near its sensitive surface. When a finger approaches or touches this area, an electric field variation occurs, which the IC detects and interprets as a touch signal, generating a digital output easily read by a microcontroller like the ESP32-S3.

The TTP223 features automatic calibration, with a recalibration period of about 4 seconds when no touch is detected, ensuring precise detection over time and despite environmental changes.

Signal Types and Operating Modes

By default, the module provides a digital CMOS output (Q pin) that goes HIGH when a touch is detected and stays LOW otherwise. It is highly versatile and configurable via option pads on the PCB:

• Output modes: active HIGH or active LOW (AHLB pin).
• Response modes: momentary (active only while touched) or toggle (changes state with each touch) via TOG pin.
• Power modes: fast or low consumption (LPMB pin).
• Open drain output available on the OPDO pin.
• Sensitivity adjustment: using an external capacitor (0–50 pF) between input and ground.

Technical Specifications

• Operating voltage: 2.0 V to 5.5 V (3.3 V compatible with ESP32-S3).
• Very low standby current, ideal for battery-powered projects.
• Response time: ~60 ms (fast mode), ~220 ms (low power mode at 3 V).
• Module size: 15 mm x 11 mm.
• Startup stabilization time: ~0.5 s (do not touch during this period).
• Max allowed touch duration: 100 seconds (MOTB pin).

Simulating the TTP223 with App Designer (MATLAB)

To realistically emulate the touch sensor’s behavior, an application was developed in MATLAB’s App Designer. It allows users to configure operational modes interactively, similar to using physical jumpers on the sensor board.

The simulation includes:

• Default signal state: HIGH (1) or LOW (0).
• Activation mode: Momentary (signal changes only while touched) or Toggle (signal toggles on each touch).

Sensor Behavior Simulation

The App Designer simulation replicates both momentary and toggle configurations:

• Momentary: signal pulse occurs during touch only.
• Toggle: signal flips on each touch and stays until the next one.

Integration of TTP223 with ESP32-S3 and RGB LED

To visually verify the touch detection, the TTP223 was connected to an ESP32-S3 board and a common anode RGB LED. The sensor’s output pin was linked to the microcontroller, and the RGB LED was configured to turn white upon touch detection by setting all cathodes LOW.

Validating TTP223 Behavior with Oscilloscope

A digital oscilloscope was used to monitor the sensor’s output in real time. The probe was connected to the TTP223’s output pin, and GND was connected to the circuit’s ground. Observations showed:

• Normal (untouched): signal remains LOW (~0 V).
• On touch: signal quickly jumps to HIGH (~3.3 V).

System Programming and Behavior

The implemented code detects capacitive touch and controls the RGB LED reliably. A ledState logic was added to prevent flickering and ensure toggling only on valid state transitions. This creates a stable, touch-activated interface.

#define TOUCH_PIN 2
#define RED_PIN 4
#define GREEN_PIN 5
#define BLUE_PIN 6

bool ledState = false;

void setup() {
    Serial.begin(115200);
    pinMode(RED_PIN, OUTPUT);
    pinMode(GREEN_PIN, OUTPUT);
    pinMode(BLUE_PIN, OUTPUT);
    pinMode(TOUCH_PIN, INPUT);
    digitalWrite(RED_PIN, LOW);
    digitalWrite(GREEN_PIN, LOW);
    digitalWrite(BLUE_PIN, LOW);
}

void loop() {
    int touchValue = digitalRead(TOUCH_PIN);

    Serial.print("Touch value: ");
    Serial.println(touchValue);

    if (touchValue == 0) {
        if (!ledState) {
            ledState = true;
            digitalWrite(RED_PIN, HIGH);
            digitalWrite(GREEN_PIN, HIGH);
            digitalWrite(BLUE_PIN, HIGH);
            Serial.println("LED turned ON!");
        }
    } else {
        if (ledState) {
            ledState = false;
            digitalWrite(RED_PIN, LOW);
            digitalWrite(GREEN_PIN, LOW);
            digitalWrite(BLUE_PIN, LOW);
            Serial.println("LED turned OFF!");
        }
    }

    delay(100);
}

This experiment successfully demonstrates how a capacitive touch sensor can be integrated into an embedded system to provide real-time digital input with visual feedback. By using both simulation and physical measurements, the sensor’s behavior was confirmed to match theoretical expectations. This highlights its reliability and usefulness for interactive embedded applications.