Hi. I'm trying to trigger a 555 timer setup to output a single-shot 12V pulse. The problem I have is, the trigger is a 3.3V output, which isn't high enough to pull the trigger input high, so my 555 is always triggered. This circuit works perfect for me when I use a 12V trigger, but not the 3.3V. I don't think my 3.3V output is open-collector. A 12V 10K pull-up didn't work. Any help appreciated.