This code uses an Arduino as a timer to control a relay with a potentiometer. You can set the timer from 0 to any number of seconds; there is virtually no limit. Fig. 1 Schematic diagram for Robojax Relay Timer V 1.0 To have finer control over the time setting, especially for times above 100 seconds, use two potentiometers with values in a 1:10 ratio (one is ten times larger than the other). For example, for coarse control, use a 100kΩ variable resistor and for fine control, use a 10kΩ resistor, and connect them as shown in Fig. 2. Fig. 2 Wiring of fine and coarse control for two potentiometers