Abstract: A current boosted positive feedback logarithmic transresistance amplifier is provided for currency validators. The amplifier has a photo-diode capable of producing a current in response to light, connected to an operational amplifier having both a positive and a negative feedback branch. A logarithmic density amplifier having a feedback resistor and a log diode connected in shunt with the resistor as a dynamic feedback to the amplifier is connected to the positive feedback branch of the current boosting amplifier by way of the log diode. The summing action at the inputs of the current boosting amplifier result in a current at the log diode that is a direct multiple of the current in the photo-diode.

Abstract: A communication system wherein a plurality of remote stations are serially connected in a communication loop to a Control Station. Communication of intelligence to and from the remote stations and to and from the Control Station is by way of high frequency bits which are introduced serially and circulate through the loop. An inoperative remote station is bypassed by introducing into the station to be bypassed a D.C. signal of controlled magnitude, duration and polarity, which, through the required instrumentalities, disconnects the station from the communication loop while maintaining the integrity of the loop.