Motor Circuit Diagrams

# Tachometer Pulse Divider Schematic Circuit Diagram

#### Author’s Background in Classic Motorbike Racing

The author is an active participant in the Classics class of the Dutch Motorcyclists Association, with a particular interest in motorbike racing. Recently, this racer undertook a significant upgrade on their motorcycle, specifically the engine. Their bike, a 500-cc BSA Goldstar featuring a single-cylinder four-stroke motor, underwent a transition from traditional contact points to a modern electronic ignition system. This alteration significantly impacted the frequency of spark production, now generating a spark for every single rotation of the motor as opposed to one spark for every two rotations with the conventional contact points. Consequently, this modification led to inaccuracies in the tachometer readings.

#### Affordable Tachometer Solution for Electronic Ignition

Purchasing a new tachometer compatible with electronic ignition systems, like the Krober unit, can be quite expensive, costing around \$250. To tackle this challenge economically, the author turned to past issues of Elektor from July & August, seeking a suitable divider circuit. The goal was to find a simple electronic solution, and it didn’t take long to identify a viable option: a monostable multivibrator circuit. With minor modifications to the original design, the tachometer now accurately displays the motor speed. The ingenious fix cost a mere \$7, resulting in substantial savings of \$243, and offering the priceless satisfaction of resolving the bike’s issue personally.

#### Understanding the Tachometer

A tachometer is a crucial instrument used to measure the operational speed of an engine, typically expressed in revolutions per minute (RPM). It finds application in various vehicles such as cars, boats, and planes. Tachometers commonly feature either an analog (dial) or digital (LCD or LED screen) display. The instrument’s semicircular design incorporates numbers from 1 to 8, with a needle indicating engine speed changes. For instance, when the needle points to 2, it signifies the engine operating at 2,000 rpm.

#### Origin and Significance of Tachometers

The term “tachometer” originates from the Greek words “tachos,” meaning “speed,” and “metria,” meaning “measure.” Its importance lies in its ability to alert operators to unexpected drops in engine speed, allowing them to anticipate potential engine failures, thereby preventing troubles related to engine performance.

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