Select your stopping place
For transport service, block the transfer. To repair the piston, block the control pulses. To protect a full warehouse, stop the source of production or transfer the flow to a backup storage facility. One lever on the exit hopper does not solve all three problems. Reference: Minecraft: hopper.
Indicate the states with a “WORK” and “STOP” sign. If the power supply means blocking, it is logical to sign the position of the switched lever “STOP”, rather than counting on other players to guess the inversion.
Simple stand with hopper
Aim the hopper into the chest and place 16 stone. While it is not powered, the stone leaves. Use the lever to apply power directly to the hopper or its control unit: the amount inside should stop decreasing.
Now place the stone in the container on top. Please note that other mechanisms may continue to insert items into the blocked hopper. For disassembly repairs, also turn off the input stream and unload the remainder from the buffer.
To connect the receiver to the chest, the following instructions will be useful: Hoppers: send items to the right container.
Clock and safe restart
A blocking repeater can be used in a pulse line: a powered repeater or comparator directed to its side holds the current state. But blocking the high state will leave the output on; it is not a guaranteed “everything is off.”
For a stop with a guaranteed zero, use the break provided by the circuit or logically inhibit the output. After stopping, wait for the remainder on the road, check that the piston has completed movement, then service. Before leaving, carry out a complete stop → start cycle with a small batch and make sure that the automation has resumed.
Direction, gain and delays are discussed separately: Repeaters: direction, delay and long signal lines.
