Universal tester circuit with VCO(voltage controlled oscillator)

This is Universal tester circuit with VCO or A voltage controlled oscillator circuit that called as VCO. The voltage signal level from input to control an amount of frequencies that generate an output, or the output frequency transform by voltage.

The basis of a function generators circuit, or an oscillator generator circuit applied in testing a lot of circuits. It can generate frequency to provides the Square wave, triangle wave, or sine wave.

The circuit in Figure 1. It is the VCO circuit to test the working of electronics circuit. Which the maximum generated frequency about of 1.2 KHz. For testing voltage under 9 volts.

Moreover, the first probe will connect directly to 9V battery terminal to the circuit tested or is input. Next, another probe is a tester for the voltage level that out of from the tested circuit or its output.

Universal tester circuit with VCO system

Figure 1 Universal tester circuit with VCO

This working principle
First, the working of the circuit has the IC1-CD4046. It is a CMOS MICROPOWER phase locked loops IC. It will be a Frequency generator controlled by voltage.

While no voltage at pin 9 of IC1. So the VCO circuit will not produce a different frequency.

Then, with a frequency of up to 1.2 kHz audio output with a piezo-BZ1. We can determined the output frequency by C1, and the resistor-R1.

Which R1 connect to the pin 11 of IC1. It controlled a the greatest frequency. But if we connect the R1 to pin 12, the output will be lowest frequency.
Next, the Zener diode-ZD1 and ZD2 prevent damage from the incoming voltage at the input of VCO. Then, the potentiometer – VR1 adjust the current level that we is testing.

This is useful when testing the circuit with high impedance. While work circuit will consume weak current, only about 3 mA.

Besides, the C1 filter current to IC1. At the same time, diode D1 is connecting to block the wrong power supply terminal.

How to build this circuit

We experiment this projects on universal PCB as Figure 2. Which they has a few components layout.

components-layout-of-circuit tester projects-by-vco
Figure 2 the components layout of this projects.

The components List

Resistors ¼ W +5%
R1: 5K
R2: 1K
VR1: 10K Potentiometer.
C1: 10uF 16V, Electrolytic
C2: 0.1uF 50V, Polyester
D1: 1N4148
ZD1, ZD2: 12V 1W
IC1: CD4046
BZ1: Peizo speaker
Two small probe.
PCB universal.

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This Post Has One Comment

  1. Your circuit is both naive and quite dangerous. “Universal” can lead the novice builder to think that this circuit could be used on line voltage. At 120 VAC, R2 will dissipate approximately 120^2/1000 = 14.4 watts. That should produce a nice light and sound show! Hopefully the exploding resistor won’t metalize the perfboard enough to maintain current flow.

    For our international friends, the show will be much more spectacular: 240^2/1000 = 58 watts!

    This danger can be avoided by including a unity gain op amp in front of the 4046 with 2 47k resistors in series with each probe input. Two resistors are used in case one fails shorted. An optional TVS behind the resistors would make the circuit even safer.

    Safety matters aside, this circuit probably will not work in the general case. Looking at a Fairchild data sheet, I see that 1uF for Cx is a boundary condition. With a 5k R1, and zero input volts if the circuit oscillates at all, it will be in the 100 to 200 Hz range – too low for any meaningful output from the piezo speaker.

    Experienced designers know to stay away from boundary conditions. Even a 0.47uF might not be low enough for this to be a generalized circuit.

    The 4046 is a poor choice for this application. The VCO isn’t designed to maintain a certain frequency for a given set of R and C. The actual frequency varies fairly widely from one manufacturer to another and even from lot to lot.

    An actual VCO chip such as the 74LS628 would be much more suitable. Even a lowly 555 would be better.

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