Frequency meter circuit

Posted on Feb 4, 2014

The input signal it is applied to a gate G and then to a counter, for a precisely period of time After this period of time, the input signal it is stopped for a while and then the cycle it is repeated. In the time of break the content of counter it is transferred in buffer memory and then it is displayed. After the load of buffer memory, the con

Frequency meter circuit
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tains of counter is reset of reason to can begin a new count cycle. The successions of this signals are conform the follows diagram : The signals COUNT, LE, RESET are generated from the base of time. A very simple base of time which contains 2 ICs can be build using the folow schematic: Unfortunately this schematics have a long time of cycle Tc = 2s. In order to make this time shorter we can modified only the times Tle and Treset. But that means to use more CIs or another solution is to use a microcontroller with the necessary software. I have used a PIC microcontroller type PIC16F84A because it is easy to programm and the power consumption is low. The program is written for the PIC16F84A but cheaper PICs (as PIC16C61) can be used. ;= Base of time =18/06/00= ; rb0 1s ; rb1, rb2. 75ms ; internal clock ; standard crystal 4 MHz XT ; ;- ; configure programmer list p=16f84A;f=inhx8m _CP_OFF equ H`3FFF` ;code protect off _PWRTE_ON equ H`3FFF` ;Power on timer on _WDT_OFF equ H`3FFB` ;watch dog timer off _XT_OSC equ H`3FFD` ;crystal oscillator _CONFIG _CP_OFF & _PWRTE_ON & _WDT_OFF & _XT_OSC ;- ; cpu init portb equ 06 count1 equ 0C count2 equ 0D count3 equ 0E ;- ; bit init w equ 0 f equ 1 ;- org 0 ; ;- init movlw 0 tris portb ; set portb as output movwf portb start bsf portb, 0 ;rb0=1 call pause ;wait 1s bcf portb, 0 ;rb0=0 bsf portb, 1 ;rb1=1 call pauza ;wait. 75 ms bcf portb, 1 ;rb1=0 bsf portb, 2 ;rb2=1 call pauza ;wait. 75 ms...

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