26-10-2017, 02:37 PM
The circuit described here can be used as an electronic mailbox. When someone releases a letter in their mailbox, the LED connected to the output stops and tells you that it has a letter. To detect the presence of a letter, we used an LDR and a light source. It has a resistance of approximately 1 megohm in total darkness and 2-5kohm in bright light. In this, the light source and LDR is so tight in the mailbox that the light will fall directly on LDR, so that when the letter falls into the box it will block the beam of light and LDR will be in darkness. The circuit gives you a visual alarm when someone throws a letter into your mailbox. This electronic mailbox circuit is based on the operational amplifier LM741, CD4001 and LDR. An operational amplifier produces an output voltage that is hundreds of thousands of times greater than the voltage difference between the input terminals.
Electronic Mailbox Circuit Diagram:
Circuit Components:
• IC
• LM741-1
• CD4001-1
• Resistors
• R1 (2.2M) - 1
• R2 (560K) - 1
• R 3, R 4, R 5 (1 K) - 3
• R6 (220k) - 1
• R7 (220E) - 1
• C1, C2 (.1uF) - 2
• Various
• LED1 - 2
• Vr1 (10K) - 1
• LDR - 1
Electronic Mailbox Circuit Diagram:
Circuit Components:
• IC
• LM741-1
• CD4001-1
• Resistors
• R1 (2.2M) - 1
• R2 (560K) - 1
• R 3, R 4, R 5 (1 K) - 3
• R6 (220k) - 1
• R7 (220E) - 1
• C1, C2 (.1uF) - 2
• Various
• LED1 - 2
• Vr1 (10K) - 1
• LDR - 1