1Hz to 1MHz Frequency Meter with Digital Display

Figure 1 

The circuit was designed to create a low cost frequency meter that will cover the range of 1 Hz to 1 MHz with a digital indication using three 7-segment displays.

• 7805 – a 3-terminal 1A positive voltage regulator with output transistor safe area compensation, internal short circuit current limiter, output voltage of 5V, 12V, and 15V, internal thermal overload protection, no external components, and current output in excess of 0.5A
• 4026 – a decade counter where the count advances as the clock input becomes high and has a maximum current of about 1 mA with a 4.5 V supply and 4 mA with a 9 V supply, which can light the appropriate segments of a common cathode 7-segment display
• 4583 – a 4-bit single-chip microcomputer designed with CMOS technology using a simple, high-speed instruction set, equipped with four 8-bit timers, a 10-bit A/D converter, interrupts, oscillation circuit switch function, and used in application with remote control transmitter
• 4007 – a 1000 Watt solid state band-specific amplifier that covers a frequency range of 400-450 MHz and provides an excellent 3rd order intercept point, high gain, and a wide dynamic range by utilizing Class A/AB linear power devices
• 556 – a dual timer that is highly stable device for generating oscillation or accurate time delays used in pulse width/position modulation, sequential timing, time delay generation, linear ramp generator, precision timing, and pulse generation due to its features such as normally open and normally off output, temperature stability, output and supply TTL compatible, adjustable duty cycle, and operates in both astable and monostable mode

The input signal is being regulated by IC1 as it performs the functions of a Schmitt trigger which is a discrete comparator with hysteresis, whose output has two possible states just like other multivibrators. The hysteresis refers to the difference between the positive and negative thresholds. It changes the signal to a level that is acceptable as an input for IC2-3-4. The input of pin1 on IC2 contains the tenth pulse which produces the carry pulse in the pin5 of IC3. Simultaneously, this scenario causes the zero indication in DIS1 while the IC3 causes a one indication of DIS2. In the event that the tenth pulse is reached by the input of IC3, DIS2 will indicate zero while the DIS3 will show one. With the display in the right order, the total indication would be 100.

The output of IC4 pin5 can be used to turn ON the decimal point in DIS1, showing the exceeding measurements. One half of double timer IC5A begins the timing while switch S1 interrupts the time in 1sec or 1ms. The second half IC5B produces an indication in 2 or 3sec during the interruption with the interruption initiated by a RESET pulse. The connection of Q1 & IC1 should be far from input jack to prevent high frequency parasitic signals. A low frequency in the input is applied by using S1 while the TR2 regulates the suitable frequency meter source with a 9V supply.

R1= 8.2Mohm
R2-9= 100Kohm
R3= 470Kohm
R4= 470 ohm
R5-6-7= 10Kohm
R8= 3.3Mohm
C1-2= 1uF 63V Mylar
C3= 47uF 16V
C4= 100nF 63V

C5= 2.2uF 16V
C6= 10uF 16V
C7= 10nF 63V Mylar
C8-10= 1nF 63V Mylar
C9= 1uF 16V
TR1= 1M ohm trimmer
TR2= 1Kohm trimmer
Q1= 2N930
IC1= 4583

IC2-3-4= 4026
IC5= 556
IC6= 4007
IC7= 7805
DS1-3=Display 7 Seg. Comm. Cath.
S1= ON-OFF mini switch
S2= 1X2 mini switch

The digital frequency meter can be reliably used in laboratories by covering the frequency areas of all the trade generators. Other types of frequency meters are used in a variety of industries such as monitoring of vibration levels from heavy equipment, verifying the RF frequency signals of electronic circuitry, and used with RF signals to provide high degree of measurement accuracy with data calibration.

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