A simple device that can be used in applications, where it is necessary to delay the activation of any device. For example, it can be used in the car to delay the switching on lights. In this way, they will be switched on after the engine is started.
• Delay time adjustable within 2-120 seconds.
• Output relay with contacts 230V AC / 8A.
• Power supply: 12-15V DC.
• PCB dimension: 30×42mm.
• Electronic Kit – soldering required.
Schematics of adjustable delay switch is shown in Figure 1. Assembly diagram is shown in Figure 2 in the user manual. The device is based on the 4541 timer chip. It is configured to work as a timer with adjustable time delay. Resistors R1, R2, potentiometer PR1 and capacitor C3 are components of the internal oscillator of U1. They affect the length of the delay time. With the PR1 potentiometer, user can set a delay time of 2-120 seconds. The output Q of the integrated circuit U1 controls the transistor T1 that powers the output relay. The D2 is overvoltage protection diode. It protects the transistor against damage when the PK1 relay is switched off. The LED indicates that the relay is powered.
Assembly and test
Assembly is typical and should not cause problems. Assembly of the device starts with resistors and other small-sized components, and ends with the installation of electrolytic capacitors, relay and screw terminals.
The device should be powered with 12-15V DC. For heavy load control, pay attention to the load on the relay contacts and the PCB tracks. Copper wire can be soldered to improve the load capacity of the PCB tracks.
R3, R4: 4,7kΩ
PR1: Trimmer potentiometer 100kΩ
D1, D2: 1N4148 or similar
LED: LED diode