How to Use 556: Examples, Pinouts, and Specs

The 556 Dual Timer IC is a versatile integrated circuit that combines two 555 timer circuits in one package. This component is widely used in electronics for generating accurate time delays, oscillation, and as a flip-flop element. Common applications include timers, pulse generation, LED and lamp flashers, tone generation, and logic clocks.

• Supply Voltage (Vcc): 4.5V to 16V
• Output Current (Sink/Source): 200 mA per timer
• Power Dissipation: 600 mW
• Operating Temperature: -40°C to 85°C
• Timing Range: Microseconds to hours
• Package: 14-pin DIP (Dual In-line Package)

1. Monostable Mode (One-Shot): Connect a trigger pulse to the TRIG pin. The OUT pin will go high for a duration determined by the RC network connected to the THRS and DISCH pins.

2. Astable Mode (Oscillator): Leave the TRIG pin unconnected and use an RC network to set the oscillation frequency. The OUT pin will produce a continuous square wave.

3. Bistable Mode (Flip-Flop): Connect the TRIG and THRS pins to control the state of the OUT pin. The OUT pin will toggle between high and low states based on the inputs.

• Ensure that the supply voltage (Vcc) is within the specified range.
• Decouple the power supply with a 0.1 µF capacitor close to the Vcc pin to reduce noise.
• Use pull-up resistors on the RESET pins if they are not used to avoid accidental resets.
• Avoid connecting outputs directly to high-current loads. Use a transistor driver if necessary.

• Timer not starting: Check the RESET pin is not held low and that the TRIG pin receives a low pulse.
• Output stays high or low: Verify the RC network values are correct and that the CONT pin is not improperly biased.
• Inaccurate timing: Ensure capacitors are non-polarized and that the supply voltage is stable.

• Double-check the pin connections and ensure proper grounding.
• Replace capacitors if the timing is inconsistent, as they may have degraded over time.
• Use a multimeter to check the voltage levels at the pins to ensure they match expected levels.

// Example code for using the 556 timer in monostable mode with an Arduino UNO

const int triggerPin = 2; // Connect to TRIG1 of 556
const int outputPin = 13; // Connect to OUT1 of 556

void setup() {
  pinMode(triggerPin, OUTPUT);
  pinMode(outputPin, INPUT);
  Serial.begin(9600);
}

void loop() {
  digitalWrite(triggerPin, LOW); // Send a low pulse to trigger the timer
  delay(1); // Wait for 1 millisecond
  digitalWrite(triggerPin, HIGH); // Set it back to high
  delay(1000); // Wait for the output to go low (depends on RC values)

  if (digitalRead(outputPin) == HIGH) {
    Serial.println("Timer is ON");
  } else {
    Serial.println("Timer is OFF");
  }
}

Remember to adjust the delay based on the RC time constant for your specific application. The above code is a simple demonstration and may require modifications to work with your setup.