An OR gate takes in two (or more) inputs, and if one or more input is 1, the output will be 1. This would require 3x 555’s as shown below. To keep things uniform, the AND blocks are represented in their single 555 configuration (ie. the TRIG/THRES input is inverting).

It seems like a waste to do this when we can accomplish the same result with some diodes and a pull-down resistor. However, this gate cannot be cascaded due to the forward voltage of the diodes, doing so may change the logic level of the output. As a precaution the diodes should have low Vf and leakage current.

One last comment is that we can make a NOR gate using two 555’s as shown below. Both the 555 NOR gate and diode or gate will be used in this design. In general, the 555 OR gate will be avoided to help reduce the overall footprint and cost of this widget.