Hall effect ICs are used as proximity sensors for applications such as proximity detection and angular velocity measurement of rotating mechanisms. Hall effect devices can detect mechanical rotation without mechanical contact. This harmless detection is based on the magnetic properties of the Hall effect. Current flowing through a semiconductor in the Y direction produces a negligible potential difference in the X direction (Figure 1). When there is a magnetic field in the right direction (Z direction) of the current, a displacement voltage appears in the semiconductor in the X direction. This effect is the Hall voltage VH.

Hall effect ICs detect electrical displacement, signal adjustment, and increase hysteresis. Basically, the device measures the electric field generated by the magnetic field in the X direction on the semiconductor. Therefore, if you place the semiconductor in an electric field with sufficient amplitude in the X direction, the Hall effect device can also detect the electric field.

The design of the internal combustion engine requires a precisely controlled firing sequence. Microcontrollers that control engine parameters not only have to modify the ignition relationship for the piston position, but also require feedback on various valve timings in more advanced engines. In addition, this novel method is a simple way to measure the ignition timing, which is useful for diagnostic aids and engine troubleshooting hardware. Even the most basic carburetor adjustment on the mower requires a measure of the engine's speed per minute. A four-stroke small engine produces a spark every time the engine turns. Therefore, the detection of this spark is a direct representation of the engine's speed per minute.

Simply place the Hall effect IC in the correct direction next to the spark plug line and use its electric field to measure the spark plug pulse. Simple isolation between the device and the spark plug wire is achieved with electrical tape. Since the Hall effect IC has internal signal conditioning and hysteresis, the fundamental frequency can be read from the device without adding components, which is completely different from the traditional current transformer method.

The circuit in Figure 2 converts the pulse from the Hall effect into a DC voltage that most common voltmeters can read. The Hall effect IC provides an open collector output. You only need one pull-up resistor. Select C1 and R1 to adjust the output voltage based on the frequency range that the charge pump section of the device will encounter. For a four-stroke single-cylinder engine, 5000 r/min is sufficient.

The circuit provides an output voltage of up to 5V and requires a 9V battery supply voltage. Working in a straightforward manner: pressing the Hall effect IC on the spark plug line, the voltage on the DVM (DMM) can be interpreted as the number of revolutions per minute. Since the measurement is non-intrusive, this method can be easily reproducible or analyzed for multi-cylinder engines. The measurement of the car engine is slightly different. The car engine has a mechanical switchboard that produces a spark every two engine revolutions. An ignition system without a switchboard and an ignition coil per cylinder produces a spark every two engine revolutions.

The circuit itself provides high voltage insulation due to no electrical contact with the ignition system. Therefore, only the logic level compatibility problem remains with the interface to the microprocessor and microcontroller. The Hall-effect IC's supply voltage ranges from 4.5 V to 24 V DC, making it suitable for standard 5V processors and automotive voltages. Multiple sensors can be connected to provide ignition diagnostics and timing analysis for automotive applications.