555 pocket digital frequency meter circuit diagram

The circuit uses an ordinary digital quartz electronic watch, solders the crystal, and connects the circuit as shown in the figure to form a digital frequency meter .

Add the signal to be measured to the E and F terminals, limit it through R6, D3, D4, etc., and adjust RP1 to control the intensity of the input signal. When measuring, press K5 once, the monostable delay circuit of IC 2 is set, CK 2 and CK3 in the four analog switches IC3 ( CD 4066) are closed, CK1 is disconnected, the "memory" circuit in the watch core is cut off, and the signal to be measured After CK2, R5, and C4 are added to the D point of the watch core, the frequency division and counting circuit of the watch core starts to work. When the preset time is up, pin 3 of IC 2 turns to low level, CK2 and CK3 are disconnected, CK 1 is closed, and the signal to be tested is transferred to the "memory" state. When reading, just press K4, and the frequency of the signal to be measured will be displayed on the LCD panel. The timing time of switch K6 is divided into two levels: 33 seconds and 328 seconds. During debugging, when adjusting RP3 to the 2nd gear, the timing time is 328 seconds; when adjusting RP2 to the 1st gear, the timing time is 33 seconds.

Point A in the picture is connected to the positive electrode of the electronic watch, point B is connected to the upper function key of the watch core, point C is connected to the negative reed of the watch core, and point D is connected to any solder joint of the quartz crystal. When the reading on the LCD screen is at level 1, the frequency value must be multiplied by 1000Hz, and when the reading on the LCD screen is at level 2, the frequency value must be multiplied by 100Hz.

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