1MHZ Digital Frequency Meter

Source :: http://users.otenet.gr/~athsam/frequency_meter.htm


This circuit is a frequency meter, low cost. It covers region 1HZ until 1MHZ. The IC1 schmitt trigger that it regulates the signal of entry and him changes in reasonable level suitable for the IC2-3-4. With the tenth pulse in the entry of IC2/1, is produced a pulse '' carry '' in the IC3/5. The same moment the IC2 causes the depiction in the DIS1, show [0], the IC3 causes the DIS2, to show [ 1 ]. When in the entry of IC3 it reaches and the tenth pulse, the DIS2 show [ 0 ] and the DIS3 show [ 1 ], (with total depiction 100, having the display in right order). The exit '' carry'' off IC4/5, can be used in order to it turns on the decimal point (comma) the DIS1, in order to it shows a situation over the limits of measurement. The timed begins with the one of half double timer (IC5A). Switch S1 select the interruption the time in 1sec or in 1ms. At the duration of this interruption, second half the (IC5B), it produces a interruption of depiction 2 or 3sec., at the duration which counter cut off by the entry and the displays remain OFF. In the end of depiction, a pulse RESET, begins the interruption of time/depiction. The critical point is round the Q1-IC1, which should be placed as long as it becomes more near in the jack of entry, to reject of parasitic signals of high frequency. For the regulation, we can use a frequency meter good precision (if you do not have you are lented) and a generator of signal. We put switch S1, in place [HZ], we apply in the entry a low frequency and we regulate the trimmer TR2, so that we take the right clue, which should suit with source frequency meter. We repeat also the regulation for the department of KHZ, with a higher frequency. The supply of circuit becomes with a battery +9V, if it is used as portable or from suitable power supply if it is incorporated in some unit that exists already.


Part List

R1= 8.2Mohm C5= 2.2uF 16V IC2-3-4= 4026
R2-9= 100Kohm C6= 10uF 16V IC5= 556
R3= 470Kohm C7= 10nF 63V Mylar IC6= 4007
R4= 470 ohm C8-10= 1nF 63V Mylar IC7= 7805
R5-6-7= 10Kohm C9= 1uF 16V DS1-3=Display 7segment Comm. Cath.
R8= 3.3Mohm TR1= 1M ohm trimmer S1= ON-OFF mini switch
C1-2= 1uF 63V Mylar TR2= 1Kohm trimmer S2= 1X2 mini switch
C3= 47uF 16V Q1= 2N930
C4= 100nF 63V IC1= 4583 [Dual Schmitt Trigger]