Telephone charge meter with four minute cycle - has several timers and optical or acoustical signal generators to warn user of approach to end of timed period

摘要

The telephone charge meter circuit divides the time interval corresponding to one charge unit in at least two parts. Before the last part expires, or during the last part an optical and/or acoustical signal is delivered. The charge motor carries out this function without limitation, once it has been started. In a typical cycle, a green lamp is illuminated during a 3 1/2 minute interval. At this stage a multi-vibrator becomes unstable and changes the indication to another optical or, alternatively an acoustic signal, until a 4 minute complete timing cycle is completed. Another system has a green LED illuminated for 3 minutes followed by a red LED for one minute.