Simple Morning Alarm Circuit Using LDR and UM66

This article provides instructions for creating a light-sensitive morning alarm circuit. The circuit utilizes an LDR (Light Dependent Resistor) or photoresistor to detect morning light, which triggers the alarm section. When light is detected, the circuit produces a melodious tone. It is recommended to assemble the circuit as depicted in the schematic diagram, positioning the LDR near a window and close to the bed. The LDR's sensitivity to light should be considered to prevent false triggering. All electronic components used in this circuit are inexpensive, allowing for a low-cost home assembly, and the circuit has low power consumption, ensuring a long operational life. The light-sensing component consists of an LDR, which is a two-terminal device capable of detecting light (photons). The LDR's resistance decreases when an adequate amount of light strikes it. The circuit operates based on the switching action of an NPN transistor (SL 100). As previously mentioned, the LDR conducts current (reducing its resistivity) when illuminated, activating the transistor. The alarm section includes a Melody Generator IC (UM66), an NPN transistor (BC 548), and a speaker. The output voltage from the light sensor section drives the alarm. The tone generated by the UM66 is sent to the base of an NPN transistor to amplify the signal sufficiently to drive the loudspeaker. The entire circuit is powered by a single 6V battery.

The light-sensitive morning alarm circuit is designed to provide an effective and user-friendly solution for waking up to natural light. The core component, the LDR, is strategically placed to maximize exposure to sunlight, ensuring reliable operation. The circuit's design is straightforward, facilitating easy assembly for individuals with basic electronic skills.

The LDR operates by varying its resistance based on ambient light levels. In darkness, the resistance is high, preventing current flow and keeping the transistor in an off state. As light levels increase, the resistance of the LDR drops, allowing current to flow through the circuit. This action turns on the NPN transistor (SL 100), which acts as a switch to activate the alarm section.

The alarm section is comprised of the UM66 melody generator IC, which is designed to produce musical tones. The output from the UM66 is typically a low-level audio signal that requires amplification to drive a speaker effectively. The BC 548 NPN transistor serves this purpose by amplifying the signal from the UM66 before it reaches the speaker. This amplification is crucial for ensuring that the alarm tone is audible enough to wake the user.

The circuit's power requirements are minimal, with a single 6V battery providing sufficient energy for operation. This low power consumption is advantageous, allowing the circuit to function for extended periods without the need for frequent battery replacements. Overall, this light-sensitive morning alarm circuit is an economical and practical solution for individuals seeking a gentle wake-up experience, leveraging the natural light of the morning to trigger an audible alarm.This article helps you to make a Light Sensitive Morning Alarm circuit. The morning light is sensed by an LDR (Light Dependent Resistor) or Photoresistor and it triggers the alarming section. The circuit generates a melodious tone when light falls on it. Wire-up the circuit as shown in schematic diagram and place the LDR next to the window pane cl oser to your bed. The LDR is more sensitive to light, so make sure it will not be false triggered. All the electronic components used in this circuit is cheap, so you can make this at your own home at very low cost and it consumes very less power, hence it ensures long working life. The light sensing part consists of a Light Dependent Resistor (LDR) or a photoresistor, which is a two terminal device having the capability to detect light (Photons).

The LDR decreases its resistance when suitable amount of light falls on it. The working principle of this circuit is based on the switching action of an npn transitor (SL 100). As i mentioned above, the LDR conducts current (Lowers its resistivity), when light falls on it and make the transistor switched ON. The alarming section of the circuit consists of a Melody Generator IC (UM66), an NPN transistor (BC 548) and a Speaker.

The output voltage from the Light Sensor Section is used to drive the alarm. The tone generated by UM66 is fed to the base of an NPN transistor, inorder to amplify the signal enough to drive the Loud-Speaker. The whole circuit is powered by a Single 6V battery. 🔗 External reference