A simple architecture for a fully customizable cortical stimulator is presented. The whole device uses a 3D penetrating multielectrode array, which will be implanted in primary visual cortex (V1), offering different signal amplitude and waveforms sets. The system has been proved for injecting current (charge) in a safe, secure and precise way during acute animal experimentation. The architecture is based on a transistor based current injection stage and a microprocessor circuit with programmable waveforms. The dynamic characteristic of the stimulator provide the possibility to adapt the current level to the different working electrodes and tissue impedances. The system is specific tailored for a cortical visual neuroprosthesis for the blind.