TS 555 CN 50 duty cycle problem

[boylesg]

Can any body tell me what I have done wrong with this circuit - I just cant see it.

I am trying to implement this circuit.

Here it is on my bread board. The transistor circuit is not connected atm. R1 = 100k as per above schematic. R2 is a 10k trimpot. C1 = 10nF
But I am getting a steady 5V out of pin 3 - no oscillation whatever.

 

[KlausST]

Hi,

what does the red wire on pin5 do? It´s not according the schematic.

Klaus

 

[crutschow]

Turn the pot to its maximum resistance.

 

[boylesg]

It was connecting it to the collector of the BC548. But I disconnected it until I could figure out why the 555 was not oscillating.

 

[Easy peasy]

Put a 10uF cap from pin 8 to pin1 for starters ....

--- Updated Oct 29, 2022 ---

make sure pin 4 goes to pin 8 ...

 

[boylesg]

Put a 10uF cap from pin 8 to pin1 for starters ....

--- Updated Oct 29, 2022 ---

make sure pin 4 goes to pin 8 ...

Specifically connect pin 4 to pin 8? Instead of just to the 5V power rail?

 

[boylesg]

It was a stuffed 555 timer chip.

 

[BradtheRad]

More than once I've hooked together a 555 pulse generator (hardware) and I saw constant supply voltage on the oscilloscope. When in truth it was about 99 percent duty cycle! Low state lasted so briefly it didn't appear onscreen at first until I adjusted a few dials.

By applying various volt levels to pin 5 (Ctl pin), I change duty cycle. The 555 is constructed to do that. Yet most designs just put a capacitor to ground.