Hi all,

Sorry for such a hash of a thread title, but it's what I'm looking for, and I know it exists, because on of my devices has it. The device is a ring launcher, which consists of an iron core surrounded by a solenoid, the whole works encased in plastic. You can place a light aluminum ring around the core, and when the button is pressed the ring flies out. Your basic Eddy Current demo.

Thing is, the button is really clever, because when you press it, the system activates. But if you just press and hold it, the system will activate ONCE. Holding the button down will not fool it into providing power (and heat). In effect, the device ignores holding the button down, or repeated key presses after activation. The ignore time is about 2 seconds or so, and the active time is probably 1/10 second approximately.

I really would like to know how they did this, because we're working on an air gun connected to a compressed air tank. When the trigger is pulled, a solenoid valve will activate for roughly .25 second, to give the missile a good shove down the barrel. But, we don't want to waste compressed air, so the user should have to release the trigger before the system responds to him/her. In essence, we want the user to have to deliberately keep squeezing the trigger to get the solenoid to fire.

I originally tried this with a 555 chip, and was able to get the system to fire for .25 seconds, but unfortunately nothing I tried would make the circuit ignore a continuously pressed button.

Any ideas on where to go with this would be much appreciated.

Thanks.

 

Use an RC circuit to trigger the 555 such as below:
It will ignore the PB being pressed indefinitely.

 

Use an RC circuit to trigger the 555 such as below:
It will ignore the PB being pressed indefinitely.

View attachment 155217

Thank you VERY much. It works perfectly!