Bedside Lamp Timer

The purpose of this circuit is to power a lamp or other apparatus for a specified duration (30 minutes in this case) and then turn it off. It is particularly useful for reading in bed at night, as it automatically turns off the bedside lamp in case the reader falls asleep. After activation by the P1 pushbutton, an LED lights up for approximately 25 minutes. However, six minutes before the turn-off, the LED begins to blink for two minutes, stops blinking for another two minutes, and then blinks again for the final two minutes, signaling that the on-time is nearing its end. If the user wishes to extend the reading time, an additional half-hour of light can be obtained by pressing the P1 button again. The lamp can be turned off at the user’s convenience by pressing the P2 button. Transistors Q1 and Q2 form an ALL-ON ALL-OFF circuit that draws negligible current in the off state. When P1 is pressed, the circuit is activated, the relay is turned on, and the two integrated circuits (ICs) are powered. The lamp is controlled by the relay switch, and IC2 is reset with a positive voltage at pin 12. IC2 begins oscillating at a frequency determined by resistors R4 and capacitor C4. With the specified component values, pin 3 of IC2 goes high after approximately 30 minutes, turning off the circuit via capacitor C3. During the six minutes leading up to the turn-off, the LED blinks due to connections from IC1 to pins 1, 2, and 15 of IC2. The blinking frequency is generated by the oscillator in IC2 at pin 9. The two gates of IC1 are connected in parallel to provide a higher current output. If desired, a piezo sounder can be connected to pins 1 and 14 of IC1. Changing the brand of IC2 may alter the oscillation frequency, with Motorola ICs typically operating at a faster rate. The timing can be adjusted by varying the values of C4 and R4.

This circuit is designed around a simple timer mechanism that utilizes two integrated circuits (IC1 and IC2) to manage the timing and output control. The first integrated circuit (IC1) serves as a light indicator and can be configured to drive a piezo sounder for auditory alerts. The second integrated circuit (IC2) is responsible for generating the timing sequence, utilizing a resistor-capacitor (RC) timing network to control the duration of the lamp’s illumination.

Upon pressing the P1 pushbutton, the circuit initiates the timing sequence, activating the relay to power the lamp. The LED indicator provides a visual cue for the user, illuminating for the initial 25 minutes. The blinking sequence serves as a warning for the user, allowing them to decide whether to extend the reading time or prepare for the lamp to turn off. The circuit's design ensures that during the off state, it draws minimal current, enhancing its energy efficiency.

The use of transistors Q1 and Q2 in an ALL-ON ALL-OFF configuration is crucial for maintaining low power consumption when the circuit is inactive. The reset function on IC2 via pin 12 ensures that the timing sequence can be restarted with each activation of the P1 pushbutton. The oscillation frequency set by R4 and C4 allows for flexibility in timing adjustments, accommodating different user preferences for lamp duration.

Overall, this circuit exemplifies an efficient and user-friendly solution for managing lighting in a bedside environment, providing both functionality and convenience for users who may fall asleep while reading.The purpose of this circuit is that of power a lamp or other apparatus for a given time (30 minutes in this case), and then to turn it off. It`s useful when reading at bed by night, turning off the bedside lamp automatically in case the reader falls asleep.

After turn-on by P1 pushbutton, an LED lights for c25 minutes, but 6 minutes before the tur n-off, start blinking for two minutes, then stop blinking for other two minutes and finally blinks for other two minutes, thus signaling that the on-time is ending. If the user want to prolong the reading, can earn another half-hour of light by pushing on P1. Turning-off the lamp at user`s ease is obtained pushing on P2. Q1 and Q2 forms an ALL-ON ALL-OFF circuit that in the off state draw no significant current. P1 starts the circuit, the relay is turned on and the two ICs are powered. The lamp is powered by the relay switch, and IC2 is reset with a positive voltage at pin 12. IC2 start oscillating at a frequency settled by R4 and C4. With the values shown pin 3 goes high after c30 minutes, turning off the circuit via C3. During the c6 minutes preceding turn-off, the LED does a blinking action by connections of IC1 to pins 1, 2 & 15 of IC2.

Blinking frequency is provided by IC2 oscillator at pin 9. The two gates of IC1 are in parallel to source an higher current. If needed, a piezo sounder can be connected at pins 1 & 14 of IC1. Changing IC2 brand name, varies the oscillation frequency. In particular Motorola`s ICs run faster. Obviously, time can be varied changing C4 and R4 values. 🔗 External reference