HOW TO MAKE A PHOTO SENSOR USING IC7408

IC 7408

IC 7408 IS A LOGICAL AND GATE WHICH COMPRISES OF 14 PINS NAMED 1,2,3...SO ON FROM THE SIDE THAT HASA SPOT OR A DOT. YOU CAN SEE IN THE DIAGRAM.

THE PINS 1 AND 2 ARE THE INPUTS TO THE AND GATE NO.1 AND PIN 3 IS THEIR OUTPUT.

SIMILARLY THE OTHER AND GATES NO.2, 3 AND 4 HAVE PINS (4,5), (8,9), AND (11,12) AS THEIR INPUTS RESPECTIVELY. ALSO PINS 6,10 AND 13 ARE THE OUTPUTS TO THE GATES 2,3 AND 4 RESPECTIVELY.

THE IMPORTANT PART IS TO NOTICE THAT PIN 7 IS THE GROUND TERMINAL OR WE CAN SAY IT IS THE ZERO VOLTAGE SOURCE FROM THE TERMINAL OF THE VOLTAGE SOURCE. PIN NO. 14 IS THE POSITIVE TERMINAL TO THE VOLTAGE SOURCE.

HERE IS THE PIN DIAGRAM OF THE IC 7408

THE LETTERS A, B AND Y FROM THE DIAGRAM INDICATE THE INPUTS AND THE OUTPUTS OF THE CIRCUIT.

SO WHILE CONNECTING THE COMPONENTS TO THE CIRCUIT IT IS NECESSARY TO CONNECT THE GROUND AND THE POSITIVE VCC TO THE TERMINALS OF THE VOLTAGE SOURCE.

SO BY USING THE IC7408 I HAVE DESIGNED A SIMPLEST CIRCUIT THAT WORKS AS A DARK SENSOR OR WE MAY CALL A PHOTO SENSOR OR LIGHT SENSOR. USING THE IC AND THE LDR, (WHICH IS THE LIGHT DEPENDENT RESISTOR) WE CAN EASILY MAKE A SWITCH THAT FUNCTIONS AS AN ALTERNATING SWITCH.

WE NEED TO HAVE LOOK AT THE TRUTH TABLE OF THE AND GATE

AS WE CAN SEE FROM THE IMAGE WHEN THE INPUTS ARE LOW i.e 0-0 THE OUTPUT REMAINS LOW i.e 0. AND WHEN THE INPUT REMAINS HIGH OR 1-1 THE OUTPUT REMAINS HIGH. ALSO TO BE NOTED WHEN THE INPUTS ARE 1-0 OR 0-1 THE OUTPUT IS LOW OR 0.

SO HERE'S THE CIRCUIT DIAGRAM THAT ALLOWS YOU TO MAKE USE OF THIS PROPERTY IN AN INCREDIBLY CREATIVE WAY.

REFER THE IMAGE BELOW..

SO HERE'S  THE CIRCUIT DIAGRAM THAT I'VE DESIGNED. AS YOU CAN SEE WE'RE USING AN IC 7408, A LDR AND A BUZZER. ALSO WE ARE USING A BREADBOARD, SOME SOLID WIRES AND A VOLTAGE SOURCE. SEE ITS THAT SIMPLE!

YOU CAN ALSO MAKE THE SIMPLE CIRCUIT ARRANGEMENT ON A PRINTED CIRCUIT  BOARD (PCB) IF YOU HAVE A HANDS ON EXPERIENCE WITH SOLDERING EQUIPMENT.

ANYWAYS FOR A SIMPLER UNDERSTANDING WE BUILD THE CIRCUIT ON A BREAD BOARD.

SO FIRST WE NEED TO UNDERSTAND THE IC CONFIGURATION FROM THE DIAGRAM. ACCORDING TO THE CIRCUIT DIAGRAM THE PIN NO. 14 IS FOR POSITIVE VCC. AND THE PIN NO. 7 IS FOR ZERO VCC OR THE GROUND (WHICH IS NOTHING BUT THE NEGATIVE SUPPLY OF THE VOLTAGE SOURCE). PINS 1 AND 2 SERVE AS THE INPUT AND THE PIN 3   GIVES THE OUTPUT FOR THE AND GATE 1.

SINCE THE POWER SUPPLY IS ALREADY COMPLETE TO THE CIRCUIT AS IN FROM PINS 14 AND 7, SO EVEN IF WE LEAVE THE TWO INPUTS OPEN THE CIRCUIT WILL CONSIDER IT AS CLOSED LOOP. AND THE IC WILL PRESUME IT BE A POSITIVE SUPPLY AT THE TERMINALS 1 AND 2 . SO WE'RE GOING TO CONNECT BOTH THE TERMINAL TOGETHER

AND MAKE IT A SINGLE TERMINAL, AND THEN CONNECT IT TO ONE END OF THE LDR.

THE LDR WE USE IS THE PHOTO SENSOR. THE OTHER END OF THE PHOTO SENSOR IT CONNECTED TO THE GROUND, AS WE CAN SEE FROM THE DIAGRAM.

THE OUTPUT PIN 3 IS CONNECTED TO ONE OF THE END OF THE BUZZER AND THE OTHER END OF THE BUZZER IS CONNECTED TO THE GROUND.

NOW WHEN WE SUPPLY THE VOLTAGE FROM THE SOURCE 

, WE COMPLETE THE CIRCUIT, BUT SINCE WE ARE USING AN LDR IT WORKS AS SWITCH WHICH COMES INTO ACTION WHEN LIGHT FALLS ONTO IT. SINCE ABSORBING OF LIGHT REDUCES ITS RESISTANCE TO AN EXTREMELY LOW LEVEL WE CAN USE IT AS A SWITCH.

NOW WHEN WE CONNECT THE VOLTAGE SOURCE THE CIRCUIT GETS COMPLETED.

WE CAN SEE THAT WHEN LIGHT FALLS ON THE LDR THE RESISTANCE VALUE GETS LOW WHICH MAKES THE SWITCH CLOSE. HERE THE SWITCH IS CLOSED AND THE INPUTS GET GROUNDED. AND UNTIL THE SYSTEM IS EXPOSED TO LIGHT THE CIRCUIT REMAINS IN A SWITCHOFF STATE. AS SOON AS WE CUT THE PASSAGE OF LIGHT TO THE LDR THE CIRCUIT BECOMES OPEN AND THE INPUT GETS DISCONNECTED FROM THE GROUND STATE COMPLETING THE CIRCUIT WITH POSITIVE INPUT AND YOU'LL GET A RESULT..

GIVE IT A TRY...

APPLICATIONS OF THIS CIRCUIT..

APPLICATION OF THIS CIRCUIT CAN BE MADE IN DIFFERENT SECTORS SUCH AS FOR SECURITY PURPOSES, AUTOMATIC STREET LIGHTS, SWITCHES,ETC..

OR SIMPLY CONNECT A CLICK CAMERA OT IT AND FACE IT TO THE PASSAGE OF THE LIGHT TO SEE WHO TRESS PASSES YOUR PRIVATE PLACES...

ENJOY!!