[SOLVED] what to do with ne555 unused pins

[Zak28]

I have an oscillator were both reset and cont aren't used. Is it safe to just leave them unconnected?

 

[c_mitra]

For a conventional NE555 it does not matter. But it is not a good habit because

1. if you do not want the device to get reset by spurious signals, you should tie reset high (it is active low). That should be the default case.

2. Same with cont, if you are not using it, just leave it open or simply connect to ground via a small cap.

 

[BradtheRad]

The ctl pin usually has a capacitor attached in most schematics. By applying a voltage to this pin you can change the duty cycle. As far as I can tell, the voltage needs to be at sufficiently low impedance so it has an effect on the internal workings.

 

[Zak28]

The ctl pin usually has a capacitor attached in most schematics. By applying a voltage to this pin you can change the duty cycle. As far as I can tell, the voltage needs to be at sufficiently low impedance so it has an effect on the internal workings.

what would be the proper way to impliment that duty cycle pin into this.

 

[BradtheRad]

what would be the proper way to impliment that duty cycle pin into this.

555 IC schematic:

View attachment 144203

 

[d123]

Hi,

???You actually have asked in a forum what to do with pin 4 and pin 5 of a 555??? You need to be fast-tracked to the finalists of Engineer of the Year if such a prize exists. It's well-intentioned leg-pulling, not trolling, friend.

There are loads of online datasheets (mainly older datasheets for the 555) and application notes with good explanations, a variety of standard timer IC circuits used/in use. Sometimes it's worth searching the Internet yourself. Here are two. I can add others if you're interested and find the required time to read up on what you're doing before doing it .

View attachment Timer 555 sa and se na and ne TI.pdf pages 14 and 15, figures 18 and 19, plus explanation.


View attachment Signetics555556Timers.pdf page 11 of the pdf, figure 5a, it has an explanation too. This document is a piece of history, to be valued and shared.

Enjoy your circuits, Zak!