need help with a 555

[nestor]

Hi.
Im kind of new with the 555, so this question might be a bit stupid.
Well, I have to make a chronometer for my course of digital electronics with some counters (7490) and the clock signal is generated by a 555 and I need to make a button to pause the chronometer. Could anyone please help me with this? Thanks.

 

[k7elp60]

NE555 stop circuit

I think the easiest way is to put a 4.7k resistor from pin#4(reset) to the + supply rail. Connect a single pole normally open push button switch from pin#4(reset) to ground. When you push the the switch the 555 will stop and when you release the switch the 555 start again.

 

[TillEulenspiegel]

Hmm don't think you even have to mess with the time base (555) the 7490 as I remember ( old tech ) has a few set/ reset lines so you can use it as a stopwatch/chronograph. Get the pinout or spec sheet.

 

[DigiTan]

I need to make a button to pause the chronometer.

That pause action doesn't have to latch does it? If so, you could use a D-latch or D flip-flop, if those are allowed.