@@@F_Titel rev(olution) counter @@@F_Text @@@Bild 51.TIF The proposed circuit is a general-purpose rev(olution) counter for cars. It is suitable for 4-, 6- or 8-cylinder engines. In a traditional manner, a direct voltage is derived from the ignition pulses. The voltage level is directly proportional to the number of pulses per unit time. The direct voltage is converted by an ADC (analogue-to-digital converter) into a BCD (binary- coded decimal) signal, which is read with the aid of a decoder and a set of 7- segment displays. The requisite pulses are taken directly from the circuit breaker (CB) in the engine compartment and applied to K1. Any unwanted peaks are removed by low-pass filter R3-C6, while the level is held to a safe value by D1. The signal is subsequently amplified by T1 and then applied to monostable multivibrator (MMV) IC1. This stage converts the signal into a series of regular pulses, which are integrated by C1. In other words, the potential across this capacitor is a measure of the number of pulses, that is, engine revolutions. This voltage is measured by ADC IC3. This circuit has four BCD outputs and three digit- drives and, in conjunction with IC2, a BCD-to-7-segment decoder, drives displays LD1-LD3. The number of engine cylinders is determined by correcting the potential across C1 with the aid of divider R4-R9. Four-cylinder engines produce four pulses, six- cylinder engines, six pulses, and eight-cylinder engines, eight pulses, for every two revolutions. In the case of a four-cylinder engine, JP2 is short-circuited and the potential across C1 is applied to IC3. With six-cylinder engines, JP3 is short- circuited so that the voltage across C1 is divided by 4/6, and with eight-cylinder engines, JP3 and JP4 are short-circuited which results in the potential across C1 being divided by two. To calibrate the circuit, remove any jumpers and short-circuit the input of IC3 (R1) to earth. Adjust the offset with P3 until the display reads '000'. Next, apply a voltage varying from 0 V to 1 V to the input of IC3, measure every step with a DVM (digital voltmeter) and adjust P1 for a display of exactly the same voltage. Finally, use a good-quality rev counter as reference, or apply a suitable voltage from a function generator with digital display to K1, and adjust P2 until both readings are the same. The printed-circuit board, which is not available ready made, may be cut into two to separate the display section from the remainder. The two parts should then be interconnected by a length of flatcable between K5 and K6. In case it is desired to get a display of '3400' instead of '340' when the number of revolutions is 3400, add LD4. When only three displays are used, place JP1 as indicated. This causes the decimal point of LD1 to light to show that the display reading must be multiplied by 1000. [LEMMENS - 974072] @@@F_Klickfont @@@Klicktext U2.TXT Parts list @@@F_Text @@@F_Klickfont @@@Klickbild 11.EPS Circuit diagram @@@F_Text @@@F_Klickfont @@@Klickbild C1.EPS Component mounting plan @@@F_Text @@@F_Klickfont @@@Klickbild L1.EPS Track layout @@@F_Text
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