This paper reports the results of the operation, under active computer control, of a high‐voltage (400 kV) injector. The automation system uses a microcomputer placed on the high‐voltage deck of the ion source, which takes over some of the process control decisions, and a master IBM‐PC at ground potential. Various ion beams (p, H+2, H+3,d, He+, He2+) have been produced, proving the reliability of the system. A maximum value of 460 kV accelerating potential has been reached during the tests. The beam fulfills the requirements for the operation of a room‐temperature IH linac. By using a modular expandable computer system the acceleration voltage is continuously adjusted keeping its standard error within 0.1%. A future enlargement of the injector has been taken into account and the upgrading of the control system for an electron cyclotron resonance ion source would be very simple. ©1996 American Institute of Physics.