Hi so I am a Civil engineering student with very little knowledge in circuits so I apologize if this question is redundant or common. I am trying to apply a current through a soil sample in order to consolidate it faster using Electro-Osmosis. Polarity Reversal should theoretically speed the process of consolidation. Hence I need a circuit that will allow me to apply 10V but alternate polarity every minute for example. My sample has an anode and cathode at each end of the soil sample in a tube. I basically just need a circuit that reverse the polarity past the power supply. I need to make a circuit that applies voltage but will reverse polarity with a given time interval and I cannot seem to find a solution for this. I am applying about 10V through DC and need to have like a programmable or modular circuit where we can change the timing of the polarity reversal, say 1min for 10V and then 1min for negative 10V and back to 1 minute of positive 10V. The timing has to be long (so no AC), this is what my trouble is in. I believe the device link below is what we need but it is way to expensive for me to buy. http://www.ebay.com/itm/NEW-DIGITAL...EVERSING-RELAY-CONTACTOR-SWITCH-/190585630987 So can someone possibly give me a possible circuit with details to conduct this polarity reversal for longer intervals. Also, if you know of any cheaper devices that can do this, that would be also ideal. If you need more details let me know.