Simple Delay Timer Circuit

Description: Without the specified delay, the circuit could malfunction or even sustain damage. A capacitor, which is a crucial component of the circuit, is positioned at the other end of the base resistor rather than directly connected to the base of the transistor. When the button is momentarily pressed, a positive voltage from the supply line enters the base resistor, turning ON the transistor and subsequently activating the LED. Upon releasing the push button, although the power to the base is disconnected, the transistor continues to conduct due to the stored energy in the capacitor, which begins discharging its stored charge through the transistor. The value of the base resistor also significantly influences the timing for which the transistor remains ON after the push button is released. The inclusion of an additional transistor stage enhances the sensitivity of the circuit, allowing for larger values of the timing resistor and thereby extending the time delay range. The circuit can be modified to create a two-step sequential delay generator. This design was requested by Mr. Marco, who aims to build a circuit to control an output relay at 12V, initiated by a manual switch. He requires an adjustable time delay (potentially displayed) after the switch is released, followed by an adjustable output time (also possibly displayed) before turning off. The sequence should not restart until the button is pressed and released again. The delay after the button release should range from 250 milliseconds to 5 seconds, while the "on" time for the output to activate the relay should vary from 500 milliseconds to 30 seconds.

The described circuit employs a capacitor in conjunction with a transistor to create a delay mechanism for controlling an output relay. The circuit's operation begins with the momentary activation of a push button switch, which allows a positive voltage to flow through the base resistor to the transistor's base. This action turns the transistor ON, which in turn powers an LED or relay connected to the circuit. The capacitor, placed strategically in the circuit, stores energy when the transistor is activated. Upon releasing the push button, the power to the base is interrupted; however, the transistor remains ON due to the capacitor discharging its stored energy through the transistor.

The timing characteristics of this circuit are primarily determined by the values of the base resistor and the capacitor. A higher resistance value will result in a longer time constant, thus prolonging the duration the transistor remains in the ON state after the button is released. The additional transistor stage enhances circuit sensitivity, allowing for greater flexibility in selecting resistor values, which can further extend the timing range.

For Mr. Marco's application, the circuit can be adapted to include an adjustable time delay and output duration. This can be achieved by incorporating potentiometers in place of fixed resistors, allowing for user-defined settings. A display can be integrated to provide visual feedback on the selected time delays. The relay output can be configured to activate for a predetermined time after the push button is released, ensuring that the sequence remains inactive until the button is pressed again. This design allows for a comprehensive control mechanism suitable for various relay applications.Without the specified delay the circuit could malfunction or even get damaged. A capacitor, which is the crucial part of the circuit gets the specific position in the circuit, we can see thatit`s been placed at the other end of the base resistor and not directly to the base of the transistor. On depressing the button momentarily, a positive voltage from the supply line enters the base resistor and switches ON the transistor and subsequently the LED. On releasing the push button, though the power to the base gets disconnected, the transistor continues to conduct with the aid of the stored energy in the capacitor which now starts discharging its stored charge via the transistor. Along with the capacitor, the value of the base resistor also plays an important role in determining the timing for which the transistor remains switched ON after the push button is released.

The addition of another transistor stage increases the sensitivity of the circuit, which enables the use of larger values of the timing resistor thereby enhancing the time delay range of the circuit. The above circuit can be modified to produce a two step sequential delay generator. This circuit was requested by one of the avid readers of this blog, Mr. Marco. "I am looking to build a circuit that would control an output relay. This would be done in 12V and the sequence will be initiated by a manual switch. I will need an adjustable time delay (possibly displayed time) after the switch is released, then the output would go on for an adjustable time (also possibly displayed) before shutting off.

The sequence would not restart until the button was pressed and released again. The time after the button release would be from 250 milliseconds to 5 seconds. The "on" time for the output to turn on the relay would be from 500 milliseconds to 30 seconds. Let me know if you can offer any insight. Thanks!"