Intelligent microcomputer interface for continuous registration and storage of spectra by photon counting

Based on an APPLE II microcomputer a low-cost counting system for digital recording of high-resolution spectra has been developed. The pulses originating from a photomultiplier are converted into TTL pulses by a commercial amplifier discriminator and are fed to a homemade 30-MHz BCD-counter with variable gatewidth (between 10 μs and 8 s). An interface incorporating a 256-byte buffer makes the information compatible with the 16-bit parallel port of the microcomputer. Simultaneous registration and storage of the counts during the gate width can be performed at speeds up to 250 words of 32 bits each per second. Software suitable for recording the count rates, for simultaneous storage on floppy disk, and for subsequent evaluation on the graphic display of the microcomputer is described. The software can easily be adapted to other applications, e.g., gas chromatography, nuclear-magnetic resonance, or mass spectroscopy.