Tap Light Modification to Make It Stay ON for 40 Seconds

The project illustrates a quick modification of a cheap tap light that will take a total of 10 minutes to complete.

During its operation, a tap would cause the device to stay ON for 40 seconds and then shut OFF. The device does not use Arduino, microcontroller, or 555 IC. However, its components include the N-channel MOSFET which is responsible for the switching aside from using a momentary switch. The time is being determined by the timing capacitor based on C&R configuration. A 9V battery is sufficiently used to run the device although the system could have 4 AA cells. The white LEDs are chosen since they have way more energy, efficient, and brighter than the incandescent it comes with.

The time constant is approximated by how long it would take for the bleed resistor to reduce the starting voltage of 9V to the dropout voltage of the gate depending on the MOSFET. Since the gate capacitance is usually unknown, the values should be tested to find out the desired time constant especially when working with unlabeled parts. The momentary switches replace the existing pushbutton ON/OFF switch and they turn ON while holding them down.

Rest of the project