Digital tachometer circuit diagram based on magnetic sensor design

　　The circuit of the digital revolution meter is shown in the figure. It is mainly composed of a disk equipped with a permanent magnet, a Hall integrated sensor, a strobe gate circuit, a time base signal circuit, a power counting and a digital display circuit, etc. The counting and digital display circuit uses CMOS-LED digital display component CLlO2, which can count and display numbers.

　　The input shaft of the turntable is connected to the measured rotation axis. When the measured axis rotates, the turntable is driven to rotate accordingly. When the small permanent magnet on the turntable passes the Hall integrated sensor IC 1, IC1 converts the magnetic signal into a rotational speed electrical signal. The signal is inverted and input to the input end of NAND gate 3 through NAND gate 1, and the other input terminal of NAND gate 3 is connected to the square wave pulse signal from time base circuit IC2. This time base signal is used to control the opening and closing of NAND gate 3 to form a strobe gate to control whether the speed signal can be output from NAND gate 3.

　　When the power is turned on, the speed signal is immediately sent to the input end of NAND gate 3. If the time base signal is low level at this time, the gate is closed and the speed signal cannot pass through the gate. When the first time base signal arrives, the strobe gate is opened, and at the same time, the LE terminals of the CMOS-LED digital display components IC4, IC5, and IC6 are in a registered state. The rising edge of the time base signal also triggers the inverter composed of NAND gates 4 and 5 and the differential reset circuit composed of R4, R5, R7, C3, VD2 and VD3. The reset pulse is output by VD3 and then added to IC4, The R terminals of IC5 and IC 6 reset and clear the address counter. After completing the above functions, the time base signal remains high level within a unit time (such as lmin). During this period of time, the strobe gate NAND gate 3 is always open, and the speed signal is sent to the LED digital display component through the strobe gate, realizing counting within a unit time. At the end of the unit time, the time base signal returns to low level. At this time, the strobe gate is closed and the LE end of the counting circuit is automatically set to the strobe state. At this time, the counting content of the counter is sent to the register and its content is displayed at the same time. When the second time base signal arrives, the contents of the counter are cleared and the above process is repeated. However, the contents of the register and display remain unchanged at this time. Only after the second sampling is completed, the new test results will be updated and displayed.