Micro-Computer Control for a HB501 STEM

Abstract

Micro-computers conveniently provide the basis of a powerful data collection, display and storage system for an electron microscope. In the example described here a Vacuum Generators HB501 STEM has been interfaced with an APPLE II micro-computer. The APPLE, with 48k of available core memory and a single mini-diskette system of 256k. byte capacity, was fitted with 16 input channels of analog-to-digital conversion (Interactive Structures AI-Ø2) and 8 output channels of digital-to-analog conversion (Interactive Structures AO-Ø3).Figure (1) shows a block diagram of the system and its interconnections to the microscope. ADC channels Ø to 5 monitor the excitations of the six lenses (two condenser, one objective and three post specimen) of the HB501. These inputs are taken directly from the feedback shunt resistors in the lens power supply and fall directly in the range 0 to +5 volts required for the ADC. Channels 6 to 9 measure the X,Y coordinates and X,Y tilt-coordinates of the specimen stage, by monitoring the voltages derived from the position-sensing potentiometers on the stepping drive motors. These signals in the range ±0.5V are converted to the required 0 to + 5V level by operational amplifiers.