Jump to content
Electronics-Lab.com Community
Sign in to follow this  
autir

555 with unconnected trigger

Recommended Posts

Hello all.
I have built a simple circuit with a 555 as a monostable multivibrator on my breadboard. The circuit is the one documented in TI's 555 datasheet. The output goes to a 0-999 counter (three 7447s and three 7490s ICs). The 0-999 counter is a seperate circuit built on stripboard and works fine. I have a problem with the 555, though. When the "trigger" pin is unconnected and close to my hand the circuit starts to oscillate or counts double (produces twin pulses?). What happens?
The final circuit I want to build is one where the counter will advance by one every time two metal wires touch each other. But leaving the trigger wire unconnected causes all sort of problems. I connected a 4069 IC to the trigger wire, so as to ensure that triggering will take place only with voltage and not by accidental grounding. But the problems persisted.
I am thinking to build a 555 astable circuit with the junction of the metal wires as its power line. Or perhaps a transistor working as a switch...
Any thoughts?

Share this post


Link to post
Share on other sites

It has been several days since you posted your question, and you may have already solved your problem.

The simplest fix is using an NPN transistor, such as the 2N2222 in an emitter follower configuration.

Share this post


Link to post
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

Loading...
Sign in to follow this  

×
×
  • Create New...