Abstract: A current controller interface accepts a variable voltage at its input and develops a current at its output which corresponds directly with the input variable voltage. Its apparatus is usually associated with a program controller as an input and a microscope which has a heated element as the output. The apparatus uses a control circuit which is coupled to a controllable resistance semiconductor device, which device has an output which varies in resistance in accordance with variation in input current. The output of the variable resistance device is coupled in series with the heating coil of the microscope, the power supply and current sensing resistor. The resistor develops a feedback voltage which is applied to the control circuit so that when a change in voltage is applied to the input the output from the current sensing element will change until it balances the current being applied at the input. When the balance occurs, no further change in output current will occur.