Frequency Meter With HCMOS SMD Components

A digital frequency meter is useful in the workshop of any electronics builder or ham radio operator.

Such a device made with integrated circuits from the HCMOS series (high speed and low consumption), 6 LED digits, in SMD technology (small dimensions and lower cost price than in the case of THT technology) is described below.

The device is built in two versions, with common cathode digits or common anode digits.

All electronic components are in current production and can be purchased from here.

PCBs can be ordered from here.

Both electronic components and PCBs can be purchased from other places, there are many sites specialized in this.

The device is made in two versions that differ only in the type of LED display: with common cathode (Variant 1.1) or common anode (Variant 1.2).

Var1.1 : we start from a 4MHz oscillator made with quartz crystal X1 and NAND gate no.4 from U20.

Through gate 3 of U20, the 4 MHz signal is applied to pin 12 of U19, which is a frequency divider by 4, so that at the output we have a signal with a frequency of 1 MHz. This signal is applied to pin 1 of U18.

The lower part of the chain of integrated circuits U18...U13 forms the decadic divider of the time base.

At its input, the 1MHz signal is applied, and at pins 1 U14 and 1 U13, signals with a frequency of 100HZ, respectively 10Hz are obtained, which corresponds to a duration of the time base of 0.01s, respectively 0.1s. These two are the signals used as the time base, selectable by switch SW2.

This signal is applied to pin 9 of U21 which performs a division by 2 and gives signals with a fill factor of 50% at pins 5, 6.The signal from pin 5 of U21 opens the main gate of the frequency meter made with NAND gate no. 2 in U20, pin4. The signal whose frequency must be measured is applied to the pin 5 of this gate, applied to input J1.Through Q3, the time base signal causes LED2 to blink in time base rhythm.

The signal from pin 6 of U21 is applied to the input of the automation circuit of the counter of imput pulses, formed by gates 1,2,3 of U22 and gate 1 of U20. This circuit gives short pulses of LE (latch enable) for the memories in U7...U12 (pin5) and then resets the input pulse counter formed with the upper part of the integrated circuits U13...U18 (pin14).R47, C14 causes the counter reset pulse to have a certain delay compared to the latch enable pulse.

After counting a certain number of input pulses, during the given time base, number of pulses found in the main counter made with 74HC390, the CD4511 memory is loaded, after which the counter is reset and the cycle starts again.

U7...U12 do the binary-decimal decoding of the number of pulses stored in the memories. Also here are the drivers for lighting LEDdisplays, common cathode, U1...U6.

The current through them is limited to approx. 10mA from R1...R42.

There is also a circuit for signaling the exceeding of the measurement range formed by section 1 of U21, D1, D2, Q1 and the related passive components. This circuit, in the case of exceeding the measurement range, flashes LED1 through Q2.

The whole circuit is powered at +5V at the P2 plug.

D5 has a protective role in case of overvoltage or reverse connection of the power supply.

C1, C3, C4, C5, C11, C12, C13 (100nF/16V) are capacitors for decoupling the power supply.

Var1.2 works the same as the previous one, even if the notations are different.

The difference is that we used common anode LED displays, which are available in large numbers as components recovered from old TVs, old analog satellite receivers, or others.

The use of these LED displays requires the use of nivel inverters, in our case U7...U12 type ULN2003. Otherwise, things are the same.

Electronic components:

Var 1.1

1 330 R1,R2,R3,R4,R5,R6,R7,R8,R9,R10,R11,R12,R13,R14,R15,R16,R17,R18,R19,R20,R21,R22,R23,R24,R25,R26,R27,R28,R29,R30,R31,R32,R33,R34,R35,R36,R37,R38,R39,R40,R41,R42,R46,R57,R69 R1206 45

2 1nF C14 C1206 1

3 HDR-F-2.54_1x2 J1 HDR-F-2.54_1X2 1

4 100nF C1,C3,C4,C5,C11,C12,C13 C1206 7

5 10nF C2,C9,C10 C1206 3

6 47pF C7 C1206 1

7 BC847 Q1,Q2,Q3 SOT-23-3_L2.9-W1.3-P1.90-LS2.4-TR 3

8 10k R43,R44,R45,R48,R49,R52,R56,R58,R59 R1206 9

9 1N4148W D1,D3,D4 1N4148-SMD-KALIKYAN 3

10 10uF C6 C1210 1

11 10-40pF C8 CAP-TH_JML06-1 1

12 1N4148 D2 1N4148-SMD-KALIKYAN 1

13 Owerflow LED1 LED-SMD_L3.2-W1.5-RD 1

14 Gate LED2 LED-SMD_L3.2-W1.5-RD 1

15 10K R47 R1206 1

16 15k R50 R1206 1

17 33 R51 R1206 1

18 220 R53 R1206 1

19 10M R54,R55 R1206 2

20 T.B.0.1/0.01 SW2 SW-TH_6P-L7.2-W7.2-P2.00-LS5.0 1

21 4011AS U1,U2,U3,U4,U5,U6 7 SEGMENT DIGIT CC 6pcs.

22 CD4511 U7,U8,U9,U10,U11,U12 SOP-16_L10.0-W3.9-P1.27-LS6.0-BL 6

23 74HC390 U13,U14,U15,U16,U17,U18 SOIC-16_L9.9-W3.9-P1.27-LS6.0-BL 6

24 74HC107 U19,U21 SOIC-14_L8.7-W3.9-P1.27-LS6.0-BL 2

25 74HC00 U20,U22 SOP-14_L8.6-W3.9-P1.27-LS6.0-BL 2

26 4.0MHz X1 HC-49US_L11.5-W4.5-P4.88 1

27 5V6 D5 DO-15_BD3.1-L6.7-P10.70-D0.9-RD 1

28 DC-005-5A-2.0 P2 DC-IN-TH_DC-005-5A-2.0 1

Var1.2:

1 330 R1,R2,R3,R4,R5,R6,R7,R8,R9,R10,R11,R12,R13,R14,R15,R16,R17,R18,R19,R20,R21,R22,R23,R24,R25,R26,R27,R28,R29,R30,R31,R32,R33,R34,R35,R36,R37,R38,R39,R40,R41,R42,R46,R57,R59 R1206 45

2 1nF C13 C1206 1

3 BC847 Q1,Q2,Q3 SOT-23-3_L2.9-W1.3-P1.90-LS2.4-TR 3

4 10k R43,R44,R45,R49,R48,R60 R1206 6

5 HDR-F-2.54_1x2 J1 HDR-F-2.54_1X2 1

6 100nF C1,C2,C4,C5,C11,C12 C1206 6

7 10nF C3,C9,C10 C1206 3

8 47pF C7 C1206 1

9 Owerflow LED2 LED-SMD_L3.2-W1.5-RD 1

10 10K R58,R47 R1206 2

11 10uF C6 C1210 1

12 Gate LED1 LED-SMD_L3.2-W1.5-RD 1

13 DC-005-5A-2.0 P2 DC-IN-TH_DC-005-5A-2.0 1

14 10-40pF C8 CAP-TH_JML06-1 1

15 1N4148W D2,D1,D3,D4 1N4148-SMD-KALIKYAN 4

16 15k R50,R52,R56 R1206 3

17 33 R51 R1206 1

18 220 R53 R1206 1

19 10M R54,R55 R1206 2

20 HL1131 U1,U2,U3,U4,U5,U6 LED-SEG-TH_10P-L12.4-W17.6-P2.54-S15.24-BL 6 pcs. (reused).

21 ULN2003 U7,U8,U9,U10,U11,U12 SOP-16_L10.0-W3.9-P1.27-LS6.0-BL 6

22 CD4511 U13,U14,U15,U16,U17,U18 SOP-16_L10.0-W3.9-P1.27-LS6.0-BL 6

23 74HC390 U19,U20,U21,U22,U23,U24 SOIC-16_L9.9-W3.9-P1.27-LS6.0-BL 6

24 74HC107 U25,U27 SOIC-14_L8.7-W3.9-P1.27-LS6.0-BL 2

25 74HC00 U26,U28 SOP-14_L8.6-W3.9-P1.27-LS6.0-BL 2

26 4.0MHz X1 HC-49US_L11.5-W4.5-P4.88 1

27 T.B.0.1/0.01 SW1 SW-TH_6P-L7.2-W7.2-P2.00-LS5.0 1

28 5V6 D5 DO-15_BD3.1-L6.7-P10.70-D0.9-RD 1

PCBs it is ordered or executed according to the indications from Step3.

Materials, Tools:

Materials and tools specific to working with SMD, described here:

https://www.instructables.com/IR-Tester-With-SMD-Components/

Power supply 5V/1A as in Photo 4.3

Oscilloscope band minimum 10MHz. Any kind.

Digital frequency meter minimum 6 digits, well calibrated. Any kind.

Pulse generator. Any kind.

The entire project for Var 1.1 can be found here.

The entire project for Var 1.2 can be found here.

In both variants we find the electrical diagram, BOM, and PCBs with Gerber files and 2D , 3D views.

They can be ordered directly here from the factory or for those who have the opportunity to make their own.

I personally ordered PCBs from the factory. They can be seen in Photo 3.1.

Photos 3.2, 3.3 show a 2D view of the PCBs, designed in EasyEda.

A very good tutorial for assembling PCBs with SMD components is given here.

I used the manual soldering method with tin. The location plan of the components on the PCB is given in the project whose address I have shown above, or we can use Photos 4.1 , 4.2.

The assembled PCBs can be seen in Photo 4.3 (top view) and Photo 4.4 (bottom view).

Photo 4.4 shows the (optional) use of RC5 type plastic spacers, mounted in the holes specially provided for this in the PCBs.

Putting to work is done with the oscilloscope, after supplying the device with +5V.

We successively check the electrical signals at the output of the 4MHz oscillator (pin 8 of U20), the 1MHz signal at pin1 of U18 and the 100Hz and 10Hz signals (pin1 of U14 and pin1 of U13).

Check the existence of short LE pulses (pin5 of U7...U12) and Rst2 (pin14 of U13...U18).

The absence or improper shape of these signals may be due to improper tin soldering, faulty or misplaced components. These will be checked.

With the pulse generator, the correct lighting of the LED displays and the operation of the signal circuit for exceeding the range will be checked. The signal generated by these (TTL level) will be applied to input J1.

Calibration of the device is done with a well-calibrated frequency meter, of at least 6 digits.

Both devices are powered and after a time of at least 15 minutes, necessary for thermal stabilization, connect the input of the standard frequency meter to pin 8 of U20.

By adjusting C8, the goal is to bring the oscillator value as close to 4MHz as possible.

The range of frequencies that can be measured with these devices is from approx. 10Hz to over 65 MHz, as much as the HCMOS circuits used here allow. The waveform is TTL.

The frequency will be displayed in KHz .

If it is desired to measure other signal shapes or levels, input signal formers will be used.

If they are followed by high frequency dividers, an increase in the maximum measurement frequency will be obtained.

To lower the value of measured frequencies,with good resolution, the former will be followed by a frequency multiplier.

About this in a future article.

The consumption from the power source is approx. 450 mA, most of it being given by LEDdisplays.

The gauge dimensions are: 87X65X10 mm. for Var1.1

87X75X10 mm. for Var1.2