Question about 555 IC Timers

[Cyune]

I am using a 555 timer in astable mode between 50kHz and 200kHz and I have some questions.

If I leave pin 5 (control) open, what effect will it have on my output response?

If pin 4 (reset) is not connected to pin 8 (Vs) or the same supply voltage as pin 8, what effect does it have on the output response? For example pin 4 is connected to a different power supply or signal generator.

Thanks for your help!

 

[MikeMl]

The answer to your questions is here and here

 

[Cyune]

Thanks for the quick response MikeMl.

I don't see an answer to my questions in those links. But, I may have missed it... if that's the case please point it out to me!

 

[Ross Craney]

The reset is tied to Vcc if it is not used for reliability. It needs to be in a known state. The control pin is earthed via a 0.01 uf (I think) to prevent the possibility of high frequency runaway which will surely release the magic smoke.

 

[ronv]

When the control voltage pin is left open it is a little susceptible to noise. This has the same effect as moving the threshold so the timing may jitter. The spec. usually calls for it to be bypassed to ground to filter noise.
I don't see any reason the reset pin cannot be run from another supply (say 5 volts) the spec shows the trip voltage at .4 to 1 volt. I would not run it higher than the supply voltage though I don't see a number in the spec.. When negative the output is low.