An apparatus for automatic control of current electrodes in a measuring system for a geophysical survey, the apparatus comprising: a circuit having a first terminal connectable to a first supply terminal of a power supply and a second terminal connectable to a second supply terminal of the power supply, the circuit further comprising: a plurality of pairs of MOSFETs (metal oxide semiconductor field effect transistors) (MHO, ML0; MH1, ML1; MH2, ML2;...; MHn, MLn), each pair from the plurality of pairs of MOSFETs directly connected between the first terminal and the second terminal such that a first pair from the plurality of pairs of MOSFETs is connected in parallel with a second pair from the plurality of pairs of MOSFETs; and a plurality of current electrodes (C0, C1, C2,..., Cn) for connecting to a load (LOAD), the load being an earth formation; and a controller configured to control ON/OFF of each MOSFET (MHO, ML0; MH1, ML1; MH2, ML2;...; MHn, MLn); wherein: for each pair from the plurality of pairs of MOSFETs (MHO, ML0; MH1, ML1; MH2, ML2;...; MHn, MLn) each MOSFET forming the pair shares a common node, each common node connected to one from the plurality of current electrodes (C0, C1, C2,..., Cn), each current electrode being connectable to a different part of the load (LOAD) thereby forming a configuration comprising an array of H-bridges, said configuration of the controller being such that alternating forward and backward currents may be applied to a part of the load (LOAD) via a predetermined pair of current electrodes (C0, C1, C2,..., Cn). a circuit having a first terminal connectable to a first supply terminal of a power supply and a second terminal connectable to a second supply terminal of the power supply, the circuit further comprising: a plurality of pairs of MOSFETs (metal oxide semiconductor field effect transistors) (MHO, ML0; MH1, ML1; MH2, ML2;...; MHn, MLn), each pair from the plurality of pairs of MOSFETs directly connected between the first terminal and the second terminal such that a first pair from the plurality of pairs of MOSFETs is connected in parallel with a second pair from the plurality of pairs of MOSFETs; and a plurality of current electrodes (C0, C1, C2,..., Cn) for connecting to a load (LOAD), the load being an earth formation; and a plurality of pairs of MOSFETs (metal oxide semiconductor field effect transistors) (MHO, ML0; MH1, ML1; MH2, ML2;...; MHn, MLn), each pair from the plurality of pairs of MOSFETs directly connected between the first terminal and the second terminal such that a first pair from the plurality of pairs of MOSFETs is connected in parallel with a second pair from the plurality of pairs of MOSFETs; and a plurality of current electrodes (C0, C1, C2,..., Cn) for connecting to a load (LOAD), the load being an earth formation; and a controller configured to control ON/OFF of each MOSFET (MHO, ML0; MH1, ML1; MH2, ML2;...; MHn, MLn); wherein: for each pair from the plurality of pairs of MOSFETs (MHO, ML0; MH1, ML1; MH2, ML2;...; MHn, MLn) each MOSFET forming the pair shares a common node, each common node connected to one from the plurality of current electrodes (C0, C1, C2,..., Cn), each current electrode being connectable to a different part of the load (LOAD) thereby forming a configuration comprising an array of H-bridges, said configuration of the controller being such that alternating forward and backward currents may be applied to a part of the load (LOAD) via a predetermined pair of current electrodes (C0, C1, C2,..., Cn). for each pair from the plurality of pairs of MOSFETs (MHO, ML0; MH1, ML1; MH2, ML2;...; MHn, MLn) each MOSFET forming the pair shares a common node, each common node connected to one from the plurality of current electrodes (C0, C1, C2,..., Cn), each current electrode being connectable to a different part of the load (LOAD) thereby forming a configuration comprising an array of H-bridges, said configuration of the controller being such that alternating forward and backward currents may be applied to a part of the load (LOAD) via a predetermined pair of current electrodes (C0, C1, C2,..., Cn).