The pulse counting and delay circuitry for a threshold photoelectron-photoion coincidence mass spectrometer is presented along with the automation system using a CEC LSI 11/23 computer and CAMAC instrumentation. A switching input register and logic circuits are used to measure alternately a time of flight coincidence mass spectrum and a background accidental coincidence spectrum, at selected photon energies. The high voltage, fast rise time pulse used for time of flight analysis creates special signal isolation problems which are handled with unique pulse blanking techniques.