# How can I null the output of this circuit when a switch is activated?

Specifically, how would I cancel the Redstone signal going to the stone block? What type of logic gate would I need?

I want to be able to active a switch on the right input (in the screenshot) that will null the resulting output:

• The exact wiring requirements may depend on how you want the thing to function overall. Do you mean to turn off the signal to the branch heading to the stone block while leaving the rest of the circuit on? Do you just want the switch to turn off that torch? Commented Jan 17, 2014 at 3:54
• Turn off the signal branch heading to the stone block. I want to leave the circuit on. Commented Jan 17, 2014 at 3:55

Based on your description, you are looking for either a NAND gate, a XOR gate, or an IMPLIES gate. Which one you choose will depend on how you want the logic gate to behave when the main (A) circuit is off.

## NAND gate:

• A is on and B is on = off
• A is on and B is off = on
• A is off and B is on = on
• A is off and B is off = on

## XOR gate:

• A is on and B is on = off
• A is on and B is off = on
• A is off and B is on = on
• A is off and B is off = off

## A IMPLIES B (inverted output)

One last possibility for completeness sake is the A implies B circuit, although for the purposes of your desired output I'm inverting the output.

• A is on and B is on = off
• A is on and B is off = on
• A is off and B is on = off
• A is off and B is off = off

While I'm not too happy with the XOR gate demonstrated (it seems to be comparatively large and clunky), the Minecraft Wiki article does demonstrate a few variants for each logic gate.

• Thank you! I ended up using the IMPLIES Gate. Never heard of it until now. Commented Jan 17, 2014 at 6:47

I believe to have a much simpler solution to the problem. Have input A go directly to the output except for one piece of wire. You should dig out 1x1 block out of the ground and place the redstone in that hole. You currently input should = output, i.e input on = output on. Now 2 blocks to the side of the 1x1 hole place a sticky piston facing the hole and any full block in front. This does not include half blocks, glass or stairs. Now have input B power the piston. This cuts off the power from input A. Now...

if B=off, O=A if B=on, O=off

O is the output