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10-11-2017, 06:43 PM

I need a project report on electronic letter box

jaseela123d · 14-11-2017, 04:10 PM

The circuit explained below has been used as an electronic mailbox. When someone enters a letter in the mailbox, the LED connected to the output stops blinking, indicating that there is a letter in the mailbox. To identify the presence of a letter in the box, we have connected an LDR and a light source. LDR is a special type of resistance whose action is based on the intensity of the light that decreases in it. At the time of total darkness, the LDR resistance is about 1 megaohm whereas at the time of bright light its resistance is 2-5 ohms. In this circuit, the light source is adjusted with the LDR in such a way that the light will fall directly on the LDR, so that when a letter enters the mailbox, it will block the beam of light and the LDR will be under the darkness.

Circuit diagram of electronic mailbox:

[Image: Circuit-Diagram-of-Electronic-Letter-Box.jpg]

Circuit components:

• IC

• LM741 - 1

• CD4001 - 1

• Resistances

• R1 (2.2M) - 1

• R2 (560K) - 1

• R3, R4, R5 (1K) - 3

• R6 (220k) - 1

• R7 (220E) - 1

• C1, C2 (.1uF) - 2

• Various

• LED1 - 2

• Vr1 (10K) - 1

• LDR - 1

When someone throws a letter into your mailbox, this circuit will produce a visual alarm. The operational amplifier LM741, CD4001 and LDR are the basic elements of the circuit. The voltage that is generated at the output of the operational amplifier is hundreds of thousands of times greater than the voltage difference between the input points.

The operation of this circuit is very easy, you only need to install the LDR and the LED in the different corners of the box so that the LED light falls regularly on the LDR, as a result of it, the device remains off as the beam of light is decreasing in LDR and its resistance will be low, which in turn will cause pin 2 IC1 to move to high. Therefore, the output of pin 6 of IC1 remains high and this high signal is sent to CD4001 pin1 which is basically a NOR gate and produces output as 1 when all inputs are in low state (which can be found in the truth table ) the LED will continue to shine, noting that there is no letter in the drop-down box.

As soon as someone drops the letter in the box, the light that falls on the LDR is blocked and its resistance reaches high. Because IC1 pin 2 moves to the low state it also converts pin 6 to low status and this low to pin1 of NI1. Because of this, we will obtain the logic 0 in the pin3 output. Therefore, we will obtain logic 1 on pin 4, the output as 0 is given to gate NI2, entered by pin 3, whatever the input of pin 2, we will get a high state on pin 4. This implies that we will get 6V on pin 4.

Whatever the voltage state on pin9, we will get high voltage on pin 8 and we will go down on pin 10 of NI3, which also turns pin 12 and 13 of NI4 to low, we will also go up to pin 11, which you can find from the truth table while the docked LED will not blink. This implies that we have a letter in the drop-down box.

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