DIY Wavemaker/Powerhead Pulse Device?

[Bedroomgangsta]

Im curious to know if anyone has blueprints or has ever dried making their own wavemaker from electronics, like a pulsing potentiometer or something. I essentially would like to build something that can put the flow forward for 2-4 seconds and then reverse the flow at the same rate etc...I have a Koralia 4 in my 55DT and I tried adding a second one but it was overkill. I just would like to create more random flow then what I have got now so whos got some ideas?! If it will cost me close to as much to build one I might as well just buy one but I like doing stuff like this so im hoping theres someone whos took the time and done something like this.

[mpc]

It can be done by an inverter circuit. You have to be able to change the frequency of the supplied current. A true sin wave inverter is preferable. So you just have to search for a schematic and principles. I can say that it will be a microcontroller based circuit.
Some theory can be found here (http://www.wpi.edu/Pubs/E-project/Available/E-project-042507-092653/unrestricted/MQP_D_1_2.pdf) and few additonal lines about the topic are located here (http://www.brighthub.com/hubfolio/swagatam-majumdar/articles/74552.aspx) and here (http://www.datasheetarchive.com/dc-ac%20inverter%20PURE%20SINE%20WAVE%20schematic%20diagram-datasheet.html).