555 timer lab help

Thread Starter

dave l

Joined Feb 20, 2009
12
Here is the latest circuit:

www.longworth.cc/lab3f.jpg

It works as such: When the switch is thrown the LED flashes for 25 seconds. After 25 seconds the LED remains lit. That works the way it is supposed to work.

The problem now is the LED does not shut off. I need the circuit to reset to LED off with the pressing of a second switch.

Please help.

Thanks!
 

mik3

Joined Feb 4, 2008
4,843
Remove the two diodes and connect the led between the output of the 555 and the output of the latch via a resistor.

To reset the RS latch connect a NO push button between the R input and Vcc.
 

Thread Starter

dave l

Joined Feb 20, 2009
12
Hello,

When I hook it up as described it:
1. LED one way it flashes but doesn't light up after 25 seconds.
2. LED hooked up the other way it lights up after 25 seconds but doesn't flash.

I've tried placing resistors in every possible combination around the LED. The only way I can get it to work is with the diodes.

What do you think I'm doing wrong?

Thanks.
 
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