How does one trigger a 555 timer with another 555 timer

Thread Starter


Joined Nov 5, 2021
I have two 555 timers, both in one shot (monostable) mode.

The first has a 90 second high time, the second is 1 second. I had the output pin 3 going to the second 555's trigger pin 2. In theory, a I see it, the high to low transition should trigger the second 555 but it doesn't. I think this may be because the trigger is stuck low because the first 555's output pin 3 is low.

To try to overcome this, I put a .1uF cap from the output of first 555 to trigger pin of second 555 plus a 10K pullup on trigger pin. Still not working :-(.


Joined Mar 19, 2019
Here is the schematic. Note the pull-up resistors on the Pin 2 Trigger. Not exactly sure what you are doing. Can you post your schematic?
There are also some tricks that can be used with Pin 5 Control Voltage but those are rare and typically for audio outputs.