Hi All, I did not want to high-jack someone else's thread so started a new one. I have here a an ST 555, I have:


R1 = 2700 Ohms
R2 = 330 Ohms
C1 = 47 uF

with that Im getting a cycle time of 104.1ms with a duty cycle of 94.6% I have been trying all day to get a cycle time of aprox 1.1s with a slightly lower duty cycle of say 85%, on time of 990 ish ms & off time of 100 ish ms but Im not having any luck , could some please help me out here

Thanks


EDIT, Sorry I think I have worked it out, the 47uF should be a 470uF should it not ?

 

According to my calculations, when R1 = 2700, R2 = 330, and C1 = 470, the cycle time is 1097 ms. and the duty cycle is 90.18% on.

But when R1 = 2400, R2 = 470, and C1 = 470, the cycle time is 1090 ms. and the duty cycle is 85.93% on, which seems a little closer to your goal.

However, I just woke up from a nap and may have a brain fog.

 

The datasheet is your friend, although it could confuse the hell out of you. The TI and old National datasheets say that the duty cycle is Ra/(Ra+2Rb). This is true for Doff=(off time/period).
For the ON time, Don=(on time/period)=(Ra+Rb)/(Ra+2Rb).
If you want an 85% dutycycle (Don=.85), you can calculate that
Ra=4.67Rb.

The period T is T=0.683(Ra+2Rb)C.
If you let T=1.1, and C=47uF, then Ra=23.6kΩ and Rb=5.06kΩ.

Closest 5% R values are Ra=24k and Rb=5.1k.

See attachment

 

Thanks guy's everything confuses the hell outta me, as for brain fog I get that as well but it seems like its there from the moment I wake up and stays with me all day

Thanks