Communications

Abstract

strated makes use of an unusual kind of modularity, which is inherent in the properties of operational amplifier circuits. A very flexible system results, valuable both for experimental bread-boarding and for more permanent equipment. A 'library' facility emerges naturally, which allows the function of any module to be changed by plugging in off-theshelf circuit boards.The over-all transfer function of an operational amplifier circuit is dominated by its passive feed-back components. By splitting the feedback components from the amplifier so that they are physically independent of it, and easily accessible, it becomes possible rapidly to convert a constructional module containing the amplifier to any of a wide range of devices: integrator, differentiator, band-pass filter, precision amplifier, attenuator, multi-vibrator, flip-flop, etc. Construction is such that feedback components can be wired up experimentally on the front panel or can be accommodated neatly on a plug-in function card (the 'library edition' of the circuit). Rotary switches, potentiometers and power supply outlets are provided on the front panel and are electrically accessible both via panel sockets and at the function cards. Input and output signals communicate with the card via further panel sockets, and these also permit intermodule connexions.The system has been in use for more than 4 years, and has adequately met most instrumentation requirements of a physiological research unit. It is probable that a significant cost saving has resulted from the ability to recirculate amplifiers, function cards, and modules, rather than leaving them permanently wired for specific applications.An experimental F.M. recording system based on a low-cost cassette tape recorder.