solid state tachometer

105 solid state tachometer Only a handful of components are needed to produce this tachometer which is useful both in the car and on machine tools that require a speed indication. The visual indication is by means of a row of LED"s in a vertical or horizontal column (or even a 270° arc). The number of LED"s lit at any one time correspond to the measured rotational speed at that time. IC1 is a frequency to voltage converter. If used in a car, its input can be connected (via R1) to the contact breaker terminal of the coil (commonly marked "CB"). The output of IC1 is fed to the inputs of both IC2 and IC3. These two IC"s are cascaded, that is the ten LEDs controlled by each IC form a single line. In this case, the LEDs from IC3 will Corm the first ten in the line. The cascading link is between pin 6 of IC3 and pin 4 of IC2. An input voltage of about 1.2 V will succeed in lighting all the LEDs from IC3, above this level will be L f321 ••• R1 DI D2 D3 D4 D5 D6 D7 D8 D9 18 17 16...