distance meter for thunderstorms

lektor july/august 1983 LiI distance meter for thunderstorms The clouds in the sky are dark, giving an ominous warning of the thunderstorm that is on its way. Sure enough, the first flash of lightning is seen; it would be interesting to know how far away the thunderstorm is. The circuit described here is intended to provide the answer to that ques- tion. Light (including lightning) travels at a speed of 300,000 m/s. Sound, in this case thunder, travels in air at an average speed of 333 m/s, depending on the ambient temperature. This is the reason why the thunder is usually heard a few seconds after the light- ning flash is seen. The thunder needs about three seconds Jonger to travel one kilometre than does the lightning; this is the same as 0.3 seconds per 100 metres. The circuit puts this theoretical knowledge into practice. The 555 timer IC operates as an astable multivibrator with a frequency of 3.33 Hz; the period is 0.3 s. This is exactiy the time differential between the pro...