555 Timer Based Circuit

1. HARUN K
INTC1517523
555 Timer Based Circuit
Electronic Code Lock

2. CONTENT
 INTRODUCTION
 REQUIRD COMPONENT
 CIRCUIT DIAGAM
 WORKING EXPLANATION

3. INTRODUCTION
 In this simple circuit we are building 555 Timer IC
based Code Lock. In this Lock, there will be 8 buttons
and one needs to press specific four buttons
simultaneously to unlock the Lock. The 555 IC is
configured as a Monostable Vibrator here. Basically in
this circuit we will have an LED at the output pin 3 which
turns ON when trigger is applied by pressing those
specific four buttons. LED remains On for some time and
then turns Off automatically. The On time can be
calculated with this 555 monostable calculator. LED
represents the Electric Lock here which remains locked
when there is no current and gets unlock when current
passes through it. The combination of specific four
buttons is the “Code”, which needs to open the Lock.

4. Required Components:
 +5V Supply Voltage
 555 Timer IC
 470Ω resistor
 100Ω resistor (2 pieces)
 10KΩ resistor
 47KΩ resistor
 100µF capacitor
 LED
 Push Button (8 pieces)

5. CIRCUIT DIAGRAM

6. Working Explanation:
 We can Increase or Decrease this time by changing the capacitor value.
Now why this time is important? This time duration is the time
for which the Lock will remain open after entering the
correct code or pressing the correct keys. So we need to provide
sufficient time for user to get enter through the dNow, we know that
In 555 timer IC, no matter what the TRIGGER is, if the RESET pin is
pulled down the output will be LOW. So here we will use the Trigger
and Reset pins to build our Code Lock.
 As shown in circuit, we have used Push Buttons in the jumbled way to
confuse the unauthorized access. As in circuit, the TOP layer buttons
are “Linkers”, they all need to be pressed together for the TIGGER to be
applied. The BOTTOM layer buttons are all RESET or “Mines”; if you
press even one of them the OUTPUT will be LOW even if LINKERS are
pressed simultaneously.
 oor after pressing correct keys.

7. Now, lets discuss the internal working of the circuit. Let’s assume that
the circuit is connected on the bread board as per the circuit diagram and
given power. Now the LED will be OFF as the TRIGGER is not given. The
TRIGGER PIN in the timer chip is very sensitive and it determines the
output of 555. A low logic on TRIGGER pin 2 SETS the flip-flop inside the
555 TIMER and we get High Output and when trigger pin is given High
logic the output remains LOW.
When all the keys in Top Layer (Linkers) are pressed together, then only
trigger pin gets Grounded and we get Output as HIGH and lock gets
unlocked. However this high stage can’t be retained for long once the
trigger is removed. Once the LINKERS are released, the HIGH stage of
output merely depends on the charging time of the capacitor connected
between Pin 6 and ground as we discussed earlier. So the Lock will remain
unlocked until the capacitor gets charged. The capacitor once reaches a
voltage level it discharges through the THRESHOLD pin (PIN6) of 555,
which pulls down the OUTPUT and LED turns off as capacitor discharges.
This is how the 555 IC works in Monostable Mode.
So this is how this Electronic Lock works, you can further replace the
LED with actual Electric Door Lock using a Relay or Transistor.

8. THANKS