ELECTRONIC LETTER BOX

INOCENCIO, KING MARTIN B.ADUCA, ADRIAN G.

HERMOSILLA, KENNETH H.MARCOS, EARL QUINN CHRISTIAN

NODADO, JESS TYRONPERALTA, BEATRICE D.

TITLE: “Electronic Letter Box”

CIRCUIT FUNCTION:

The “Electronic Letter Box” uses an LDR (Light Dependent Resistor) to act as a switch when the the mail box receives letter(s). A variation of circuit designs was previously made to modify every type of reaction on how it will notify about having a letter inside but each of it falls down to one principle.

The LDR produces between 2-5 kiloohms of resistance when it receives enough luminousity and produces up to 1 megaohm when in complete darkness, therefore making the circuit approach to zero current producing low up to no voltage anymore in which it acts as open circuit when approaches to infinity.

The type of circuit we chose was with two integrated circuits, namely LM741 and CD4001, other similar type might be in use in the absence of the previously given IC’s. LM741 is basically an all-purpose operational amplifier while the CD4001 is an IC which uses NOR GATE with 14 pins.

The circuit that we will be using has a simple idea. The initial state of it where we assume that the letter box doesn’t have anything inside giving the LDR enough light by the LED (Light Emitting Diode) on the other side of the box, this means the LDR acts as closed switch leaving the second LED, indicator, lighted. The more complicated yet still simple part happens when the box received a letter which will blocked the LED to provide light for the LDR.

When the LDR is in complete darkness it acts as an open switch giving one input of LM741 an “0” or in low state which will immediately produce an output of low state “0” and becomes an input to the first NOR gate. NOR gate produces only “1” high state output when it received bot “0” in the input but because only one input is “0” it will produce “0” as output and input for the second NOR gate that will produce “1” output. This output will flow to the second input of first gate for the cycle to continue at the same time as input for the third gate which will mean any other input for the third gate will not affect its output if “0” that will be the input for the last gate producing “1” as output. This last output is connected to the n-material of the LED which means it will not produce any light indicating that there’s a letter inside.

The circuit function and indicator mentioned above is the backbone of this proposal but it might still change a bit for better result and indication. Future changes might include the IC’s that we will be using and the type of indicator yet the principle will stay compact with slight difference, occurrence of it might depend on the availability of the materials.