The first CFAM1 prototype was designed by D E Maynard in 1975 in response to requests from anaesthetists working with intravenous anaesthetics. The amplitude distribution of the CFM was modified to give a better indication of trends and the percentage activity in each of the basic EEG frequency bands was added to the display. Also added were percentage time suppression below 1 microvolts peak to peak, a direct measure of scalp muscle activity and the level of mains (line) interference. The monitor was eventually manufactured by Health Care Developments Ltd. It was replaced by the CFAM2 in 1989.
The CFAM1 trace was produced by scanning a hot pen across thermal chart paper. Slow scan enabled the pen to write, a fast movement left a blank. The system used analogue filters to pre-process the data, followed by analogue to digital conversion into a Motorola 6808 8 bit processor. The processor determined the response to control buttons and provided the galvanometer drive through digital to analogue converters.
