LED revolution counter

EE July/August 1986 881LED revolution counter A close look at the dashboards of a number of cars may reveal the use of three basic types of rev counter: first, the still most commonly found needle and round scale, analogue combination; second, a set of digital displays (often LCDs); and third, a pseudo-analogue meter in the form of multi-coloured LED bar, looking much the same as a LED-based VU meter on modern recording equip- ment. The circuit presented here belongs to the third category. However, con- trary to the straight LED bar indi- cation, this design features a round scale with a coloured LED needle imitation, just as the good old mechanical rev counter. The circuit is based on the Telefunken Type U1096B analogue input LED driver which can light one of 30 LEDs on the rpm scale, whose lower and upper indication limits may be set to individual re- quirements; e.g. the 30 LEDs may merely indicate a limited rpm range 2 1 108 R1 R2 1,15 R3 R4 R6 R7 3 R13 062 C9 12V 00 I.30mA 1N...