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...