flashing telephone light - see the phone ringing

see the phone ringing In many instances it is not only the hard of hearing who are unable to hear the telephone ringing: even with normal hearing it is often impossible to detect above the noise from the vacuum cleaner or the radio. The present circuit enables the ringing of the phone to be seen with the aid of a flashing lamp. It is perfectly feas ible to put a number of lamps in parallel and place them in different locations. Inductor L1 is attached to the telephone by a suction pad: it may be necessary to try out several pos itions on the telephone to obtain best results. A reference voltage of about 4.8 V is provided by potential divider R1/R2 and applied to the non-inverting in put of opamp IC1 directly and to the inverting input via L1/P1. The preset is adjusted to give equal levels of direct voltage at both inputs of the opamp: the output of IC1 is then logic low. When the telephone rings, an alter nating voltage is induced in L1, caus ing the potential at the non-inverting...