# how to create a 59 seconds timer

Discussion in 'Homework Help' started by Newfreak, Feb 6, 2010.

1. ### Newfreak Thread Starter New Member

Feb 6, 2010
3
0
hey guys.
im a fresh student of engineering and quite having problems on circuits.
my project is to make a 59 seconds timer or 1 minute timer using 555, 74LS47 and 74LS190 .im going to dispplay the numbers using two 7 segments.

my problem is i dont kow to make it stop at 5 and then loop again.

2. ### mik3 Senior Member

Feb 4, 2008
4,846
70
Monitor the output of the counter with a logic gates circuit. When its output reaches 59 the logic circuit will disable the 555 by driving its pin 4 low. The output of the logic circuit will feed a 2-input XNOR gate. The output of the XNOR gate will drive pin 4 of the 555. On the second input of the XNOR gate put a push button which will start the counting again when pressed.

3. ### Newfreak Thread Starter New Member

Feb 6, 2010
3
0

im all new to this kinds of stuff...

4. ### Newfreak Thread Starter New Member

Feb 6, 2010
3
0
thinking...

its so hard for me but my professor told me it was easy..

he told me to use only 74LS47,74LS190 and 74LS08, plus the 555 timer...

5. ### beenthere Retired Moderator

Apr 20, 2004
15,808
295
Use Google to get data sheets for all those IC's - use "74ls47", etc as the search term.

6. ### Wendy Moderator

Mar 24, 2008
21,839
3,051
Think AND gate, feeding a reset (or a preset number, same thing).

The number 5 is binary 101, which is not what you want. The binary number for six (110) would be where you reset.

You could use a diode gate (they work well with TTL) or a TTL gate (qty 2 7400 gates, quad NAND).

7. ### yasthicklee New Member

Feb 6, 2010
7
0
Hello friend,
I feel this can make you good

Just have a look at the image ...If u want i can give you the circuit too
I dont know how to attach a image so i have done with a word doc

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8. ### Wendy Moderator

Mar 24, 2008
21,839
3,051
But that doesn't match his part requirements.

The AND gate can pick up on the number I showed you (binary for 6), and feed into the reset pin.

The 74190 is a pretty cool chip too, since you can make it start from any number. Reset takes it to binary 0, but you can treat the preload inputs as another form of reset, and take it to any number you choose.