Combining 2 sound waves

[MCH170]

Hello, I am studying electrical engineering and don't know anything about music. My current project is to combine 2 square waves of different frequency (generated by 555 timers) into a single wave that I can then use on a speaker. Do I need to combine them using OR logic, or do I need to add them (if both waves are HIGH at a particular moment I give the speaker double the voltage)? Thanks for your help



Edited to display picture - JP

[Wonks]

You add the two outputs together.

[MCH170]

Thanks! Have a nice day.

[James Perrett]

Grab a copy of The Art Of Electronics (which is an essential text book if you are studying the subject), turn to page 234 (in the third edition - it will be different in others) and look at diagram 4.24 which shows a summing amplifier.

[Wonks]

But you could also AND them together (especially if both the waves are of the same frequency), to get a pulse wave. Change the phase of one square wave relative to the other and you can get a varying width pulse wave, which is a standard analogue synth waveform (picture from Wikipedia).



Or you can sum the waves and still change the phase of one of them to get variations in sound. It all depends on the end result you are trying to achieve.

[Wonks]

You could always split the output from the two 555s and feed into sum, OR and AND circuits and have a 3-way switch to select which output you want.