Need to "Extend" a Arduino Digital Signal
The scenario you are referring to - connecting one output to many devices - is called the fan-out. Yes, a GPIO pin has a limited amount of drive which limits the number of devices in the fan-out. 

There are two problems that are caused by excess fan-out:


Excess current draw from resistive loads
Excess capacitance from logic loads


The former is evident when you have too many LEDs connected directly to an output (with resistors, of course). The combined current draw of the LEDs exceeds the current the IO pin can provide and either damage the pin or the LEDs go dimmer than would be desired.

The latter is more evident when working with communication signals. The excess capacitance imposed by each gate attached to the output causes a low-pass filter effect which can filter out high-frequency signals or corrupt the waveforms by removing higher frequency components and "curving off" the nice clean square waves.

In normal logic systems it's common to use line drivers or buffers to allow the connection of more devices to a single signal. Devices such as the 74HC244, which is 8 buffers in one chip, are commonly employed. You can connect the inputs of all 8 buffers to one Arduino output, and each output from the buffer mirrors the input exactly and can connect to more devices than an Arduino can (each output has an extra 10mA steady-state drive capacity than the Arduino).

And yes, you can even connect the output of one buffer to the inputs of other buffers to give even more capacity.







simulate this circuit &ndash; Schematic created using CircuitLab