Coin box telephone pay signal system - gives signal at fixed time before credit expiry and independently of tariff rate

摘要

Telephone subscriber clock pulses are fed by way of one input of an AND gate and also by way of a delay device to a separator stage which is also fed from a pulse generator by way of the AND gate. A dual-operating counter receives the delayed subscriber clock pulses and also the output pulses from the separator stage and feeds a memory by way of a code converter and an AND gate. The output from the memory is combined with a signal from a coin-box credit store and delayed subscriber clock pulses to give a pay tone at a predetermined interval before the expiry of the credit. The credit expiry time depends on location of the two call participants.