minecraft-java-editionminecraft-redstone
Is it possible to send a redstone pulse as a wire turns off?
I have a machine I'm trying to build that uses a timer and I'd like for something to happen at the very end of the timer running down after it has turned off.
The only way I can think to do this is to somehow build a machine that inverts the on circuit to power a piston and when the circuit turns off the piston retracts for a while and then powers on again.
The most reliable redstone timer is this:
It seems pretty weird but chicken are the most reliable source of random! Let it wander in it's 2x1x2 cage and it will be definitely random!
When the piston is not extended, the wire is cut and goes straight to the block beside the piston, thus powering it. So the piston extends...
And the two wires get connected, so the wire no longer goes to the block, and the piston is not powered anymore, so it retracts.
The cycle repeats, making a pulser.
The concept of "blocks being powered" is quite slippery unless you fully understand it. This great video really helped me complete my understanding of it.
There is also another strange thing. It is possible to stop the pulser by putting another block near the moving one and then removing it. Even though that block is powered, the piston is not extended. However, when you cause a redstone update (by placing/removing a block or changing a redstone current) near it, it starts going again. This concept is used in Piston-based BUD Switches.
Best Answer
As mentioned by @zzzzBov, what you are looking for is called falling edge detector. The wiki has a section on these, with multiple options to choose from, like these two:
On the left, the sticky piston retracts the diamond block, allowing a signal to go through before the repeater turns off. When the power is turned on, the diamond block cuts off the signal before the repeater turns on.
The design to the right works using locked repeaters. When you unpower the input, the repeater on the right is unlocked just briefly enough to allow a signal through. On powering the input, the repeater is locked before it can change state.
Another option you have is to use a rising edge detector, also known as a monostable circuit, and invert the input using a redstone torch. There's plenty of designs available online.