Electronic Lamp Switch Including Time Delay Option

Figure 1 

The circuit has been designed to create a lamp switch operated electronically with an option of setting a delay in the time of execution of operation to reduce one or more lamps in a stairwell or any other places where this circuit may be useful.

• 4N35 – a general purpose optocoupler that consists of a gallium arsenide infrared emitting diode driving a silicon phototransistor in a 6-pin dual in-line package used in microprocessor inputs, digital logic inputs, and power supply regulators due to its features such as high isolation voltage between input and output, operating temperature up to +110ºC, and available in wide-lead spacing
• 4093 – a quad 2-input NAND with Schmitt trigger inputs integrated circuit, generally characterized by small fluctuation in voltage supply, very high impedance, outputs that can sink and source, one output can drive up to 50 inputs, high speed gate propagation time, high frequency, and low power consumption
• 7812 – 3-terminal 1A positive voltage regulator with short circuit protection, thermal overload protection, output transistor safe operating area protection, output current up to 1A, and output voltages from 5V to 24V
• BD679 – a monolithic NPN Silicon epibase power Darlington transistor with resistors and diode in a TO 126 plastic package and is typically used for AF applications due to its high current gain

The circuit can be useful to control various motor or appliances that can be connected in J3 contacts. The switches which are connected in parallel can trigger the operation and there are no limits in the quantity of switches to be used. Connected to J1 are the leads of switches via small diameter cables. The LEDs are functioning constantly by pressing each switch to be able to shed light in dark places. In the event that the switch will be placed outside, it is a must that they are ensured to be waterproof to avoid short circuit in the switch.

LED D9 is controlled by switch S2 which is connected in parallel to the J2 connector. It can be placed above the box of the circuit or near the box if not necessary. The LED of optocoupler IC1 gets triggered by pressing any of the switches, which causes the transistor to close while the gate of IC2A is grounded as its output becomes high. An optocoupler is a solid state device which uses a light emitting diode to transfer light via a barrier that is optically transparent between two isolated circuits. The capacitor C3 is charging through D2 that is near the voltage supply. The output of IC2C will become high when the output of IC2B is low. The relay RL1 is triggered upon the conduction of Q1, where the lamp is turned ON upon the closing of the relay contacts since the lamp is connected to the relay contacts. When the pressing of some switch is stopped, the output of IC2A will become low while capacitor C2 discharges via R5 and the trimmer TR1. Since TR1 is proportional to C2, the resistance of the trimmer varies with the discharge of the capacitor therefore, causing the relay to stay triggered. The time of relay operation is determined by the values of C2, R5, and TR1. To prevent the unwanted excitation of the relay due to parasitic signals in the input of IC2A, the optocoupler is used as an aid.

A single power supply is supporting the circuit with a stable range of 12 Vdc. However, the supply can be interrupted using switch S1 if needed. The diode D15 shows the indication of the circuit being powered while the conduction of the relay would turn ON the diode D12. The relay can be placed in other contact point since the power of the load that supplies the RL1 is dependent on the contacts. In the figure 2-3, the indication of LED found on each external switch is connected in two ways with the value of resistor R1 being computed. In the last figure, where a typical house connection is illustrated, the existing switch, denoted by Sw, is used in the wall of the house. The lamp turns ON independently from the operation of the circuit when the Sw is closed. The circuit will function normally when the switch Sw is OPEN.

Figure 2 

There are many types of electronic time delay switches that are used in several different types of circuits and several applications in the market. One of the uses is in high current and low voltage power circuits like in automobiles, vehicles, and the like. The connection of time delay switch in series with the DC power circuit is often desirable in such circuits. To be able to provide maximum power transfer at the end of the time delay period, the time delay circuit is required to have a capability of handling the load current in the circuit during the time delay period.

The time delay switch is suitable for mounting with two mounting lugs on most standard square boxes. It is recommended that deep boxes are used where extra space is required for additional cables, although it is designed for acquisition in shallow surface boxes or in plaster depth flush boxes. These time delay switches are not only found in stairwells but also in entrance lobbies, in new or retro-fit applications, in corridors, in meeting rooms, and in store cupboards to control lighter of dwelling. It can also be connected to bathroom exhaust fan or bathroom light where the turning OFF of the switch would turn OFF the light but the fan would continue to run for a user specified time.

For security purposes, a time delay switch or TDS can be linked to a timer that a user can set. The timer goes into effect upon activating the switch by the user. This technique can be used prior to vacation so that the lights will turn ON and OFF as though someone was home, to prevent criminals from breaking in. in some public buildings and hotels, these switches are being used to turn the hallway lights OFF when not in use. An example is giving people enough time after the switch is turned ON to reach their rooms before the lights turn OFF. They can also be used in laboratory research for creating very controlled conditions for an experiment. They can also be built in ornamental fountains, automotive ignition systems, and other imaginable electronic items.

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