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.
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.
The components List
Resistors ¼ W +5%
ZD1, ZD2_______12V 1W
Two small probe.
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