555 timer help

[mphotis]

??? please help me!!!

Im in desperate need of a design for a clock/timer.

MY project requires that i design and build a circuit that will act as a stopwatch and a countdown timer. eg, when activated, the circuit must count up in seconds. it can then be reset. it must also have the ability to be preset with a time which will then count down on a seven segment display. when the time is finished an alarm must sound.

Im required to use discreet components, (nothing programable).
I have to use a 555 timer.
im alowed to use BCD to 7 segment displays.

any help will be appreciated. im quite lost as to what to do.
thanx
mike

[mixos]

Hello

Read this:

Digital Stopwatch 0-99sec
http://www.electronics-lab.com/projects/oscillators_timers/014/index.html

and then read this:

Digital Stopwatch 0-60sec
http://www.electronics-lab.com/projects/oscillators_timers/015/index.html

To understund the basic of a digital stopwatch. Then you will have to make it also reverse count with a little research. You can replace the timebase using the 555 timer.

Hope this helps for beggining.

Also i attach you exaclty the same schematic as "Digital Stopwatch 0-99sec" but in another design that will help you to understund it better.

[Guest Kasamiko]

I have a circuit here exactly as what you need.. ;D
Using LM555 as a clock source, CD4553 3-digit BCD counter and 74LS47 BCD TO 7-SEGMENT DECODER/DRIVER.
Unfortunately, It's on paper and I dont have a scanner. :-[ :-[
If you can wait I can draw it for you just give me some time..

[MP]

I have moved the posts by SOHAIL to the microcontroller area since it was a request for a microcontroller based timer.
Please find it here:

http://www.electronics-lab.com/forum/index.php?board=10;action=display;threadid=913;start=0

SOHAIL, this will give you better exposure and I hope that you will get a quicker answer to your request.

MP

[Kevin Weddle]

A 555 timer is a simple circuit that includes voltage divider resistors, two opamp comparators, a transistor, and a flipflop or SR latch. The disadvantage of this circuit is the extra components that are not used in some applications. I am not sure what particular function involves the use of all these devices. Anybody know?