CONSTRUCTION OF A SECURITY SYSTEM

CONSTRUCTION OF A SECURITY SYSTEM

USING NAND GATE

INTRODUCTION:

Secu­rity is a topic of con­cern to every­body because bad things are hap­pen­ing around us and it is grow­ing worse every day. There are sev­eral ways to approach inse­cu­rity and deal with it. It can be the rich way or the cheap but effec­tive way, it all depends on your person.

For those who doesn’t have much to afford the bet­ter or higher secu­rity mea­sure around their home and prop­erty I hope this piece of work can help in some way if you can do it.

That bur­glar could have been stopped, that bad man with wicked plans could have been star­tled and send run­ning home by con­fus­ing him and alarm­ing about the dan­ger with this devices you are about to see. It is extremely use­ful handy and cheap too, it has a wide range of appli­ca­tion or style you could use it.

CIRCUIT DESCRIPTION OPERATION ANALYSIS

I assume we all know what elec­tronic logic gates are and their types? Well, first a logic gate is an elec­tronic cir­cuit which makes logic deci­sions. It has a sin­gle out­put and one or sev­eral inputs. The cir­cuits we are about to use are logic gate based and we are going to actu­ally see how we can make these gates using diodes, tran­sis­tor and IC form­ing a sys­tem or device that will help us do some work. There are many types of logic gates, let’s treat NAND gate now… but if you are inter­ested in see­ing the already treated AND gate click here.

2. NAND or (NOT-AND) gate

• NAND gate using transistors
• NAND gate using IC

NAND GATES (NOT– AND) GATE    

The NAND gate is the sec­ond most pop­u­lar elec­tronic logic gate after the AND gate and its oper­a­tion is dif­fer­ent in that, it works in reverse or do the oppo­site of what AND gate does. The table below should explain it well:

A	B	Out­put (x)
L	L	H
L	H	H
H	L	H
H	H	L

A	B	Out­put (x)
0	0	1
0	1	1
1	0	1
1	1	0

A	B	Out­put (x)
-	-	+
-	+	+
+	-	+
+	+	-

NAND Gate Symbol

Com­pare the three tables above with that of AND gate pre­vi­ously treated and you will see the difference.

The above implies that in AND gate, 1x0=0 then in NAND (NOT AND) gate 1x0=1. Imply­ing that in NAND gate, cross­ing pos­i­tive with neg­a­tive will give you pos­i­tive and the same the other way round. The only way to have a neg­a­tive out­put result is to cross pos­i­tive with pos­i­tive. And we can achieve this fit elec­tri­cally by using some resis­tors and a pair of tran­sis­tors or an IC like IC4093.

NAND gate using transistor

NAND Gate cir­cuit with tran­sis­tor and resistor

NAND Gate cir­cuit with tran­sis­tor and resis­tor 2

NAND Gate cir­cuit for dif­fer­ent use

Above is the tran­sis­tor cir­cuit for a NAND gate which is made of two tran­sis­tors (optional) and three resis­tors (optional). The tran­sis­tor Base resis­tors pro­vide a for­ward bias­ing cur­rent good enough to open the pas­sage for cir­cuit cur­rent to pass from Emit­ter to col­lec­tor with­out dam­ag­ing the tran­sis­tor. When the trig­ger is (closed) the tran­sis­tors do not con­duct because there is no Base cur­rent to for­ward bias it in that, the Base cur­rent that comes is grounded via the Emit­ter of the tran­sis­tor (remem­ber Emit­ter and Base ter­mi­nals do con­nect or link together inter­nally) and so they will remain in an OFF state until when the trig­ger is released (open) the bat­tery cur­rent is seen at the Col­lec­tor ter­mi­nal of the tran­sis­tor imply­ing that any­thing put at the Out­put point at the col­lec­tor ter­mi­nal will receive cur­rent and be acti­vated as long as the sys­tem remains in this state.

The trig­ger point is the point to acti­vate what­ever thing you feed at the load point; be it a piezo buzzer or any other alarm device, be it a relay for acti­vat­ing some­thing big­ger it’s up to you. But what I know is that for exam­ple if you place a buzzer there at the load point it will sound an alarm when­ever the (always closed) trig­ger is opened. We can apply this thing to work for us in a more mature way as demon­strated in the dia­gram below.

NAND Gate cir­cuit in a box

The dia­gram fea­tures this cir­cuit in a big box and it is con­cealed in another tiny almost invis­i­ble box or bag placed at the cor­ner of the box hid­den. Indi­cat­ing that once this cir­cuit is fin­ished one should con­ceal it in a black rub­ber plas­tic or tape it or put it in a tiny box to hide it well and make it smart. Assum­ing you want to mount this fin­ished device in a brief case so that an unau­tho­rized per­son can­not open it when you don’t want it to be opened, if he tries to open it, he blows an alarm it is just for you to power it with a 9 volt dry cell bat­tery switch it on and:

• Take point (1) of the trig­ger and con­nect it neat and clean to the upper hook of the case and
• Take point (2) of the trig­ger and con­nect it also to the lower socket of the case in which the hook do clip fix when the case is closed. Make sure in every con­nec­tion you make the wires con­tact the metal­lic / socket respec­tively. And there you go: once some­body tries to open your box unau­tho­rized the logic gate is awak­ened because the bat­tery cur­rent is allowed to reach the buzzer by that action there­fore acti­vat­ing the alarm buzzer which will con­tinue to sound as long as the box is open except it is closed.

NAND Gate cir­cuit mounted on a door

Also this device can be placed in a door in the same man­ner as demon­strated above so that, if some­one opens the door, the alarm sounds. Apart from using the piezzo buzzer alarm at the load point in the cir­cuit, you can use things like relay so that a heavy cur­rent load can be manip­u­lated once the device is trig­gered. With a relay you can con­nect a secu­rity light, sound sys­tem or even your car out­side to it so that once the device is trig­gered by whoso­ever that tries to open your thing the secu­rity light, sound sys­tem or car engine is ON there­fore scar­ing the intruder away and warn­ing you of an intruder at the same time.      

NAND gate using IC 4093

NAND Gate cir­cuit using IC4093

From the IC pin outs dia­gram one can see that the IC inter­nal struc­ture is made of four inde­pen­dent NAND gates all pow­ered by the one source. Both the input and out­put pins com­bine to form a total of 14 pins out from the IC. Now since what we are going to do involves only a sin­gle input and out­put we are going to use only one of these NAND gates inside and that is to say three pins only excep­tion of the power pins 14 and 7. And as seen the pin we are going to use are the 8, 9, and 10 pins. Where pin 8 and 9 are the inputs and pin 10 the output.

The dia­gram below is sim­ple and self-explanatory