In actual production and life, it is often necessary to test the continuity of the line. The commonly used method is to use the multimeter's resistance file detection, which is simple and practical but has its limitations. Usually, the pen of a multimeter is only about 1 meter. It is difficult to detect when the distance between the two terminals exceeds two meters. If the ends of the line being tested are in different rooms, then you have to use other methods. In response to the above problems, this new circuit on-off detector was designed.
First, the working principle
This phenomenon is often found in electronic production. When we touch one input of the power amplifier circuit by hand, the speaker will have noise due to human clutter. If so, why can't we use this phenomenon to detect the continuity of the circuit?
First we enter an audio signal at the end of the line under test. { can only be low frequency, not high frequency. If the frequency is too high, it will affect the correct rate of detection.) If the circuit has no open circuit fault, this audio signal will be transmitted to the other end of the wire through the wire, and we will use the audio amplifier to detect it. The audio amplifier will sound to indicate that the circuit is normal. On the contrary, if the circuit has an open circuit failure, no sound will be produced.
Circuit continuity detector working principle diagram
This is how the circuit continuity detector works.
Second, the circuit diagram
The circuit continuity detector consists of two parts, an audio signal generator and an audio signal amplifier.
1, audio signal generator
The audio signal generator is mainly composed of KD-9300. The KD-9300 series music integrated circuit is a large-scale CMOS integrated circuit. It stores a world famous song or popular song, such as Happy Birthday, Honghushui, etc. The typical working voltage is 1.5. V-3V, triggers a memory cycle once.
The audio signal generating circuit made by using the chip is as shown in FIG. 2:
Audio signal generating circuit made of the chip
The audio signal generator has few external components, only one triode and one switch. When welding, the tripolar battalion can be directly soldered to the hole reserved by the music chip, and then a line is drawn from the collector of the triode to connect the crocodile. Clip, the power supply uses a 7th battery, the circuit current is very small, so there is no power switch. When the switch K is pressed, the circuit is triggered and the collector of the triode produces an audio signal that is output through the alligator clip.
2, audio signal amplification output
The circuit principle is shown in Figure 3.
The audio signal is sent to the power integration block TD2822 through the probe, and the weak audio signal is amplified, amplified, and output through the pins 1 and 3 to drive the speaker to sound. The speaker volume here is very small.
Therefore, it is recommended to use a buzzer instead. The shortcoming is that the circuit after the replacement has poor sound quality and serious sound distortion, but our circuit can say that there is no requirement for sound quality.
Third, the selection and installation of components
This circuit continuity detector does not require high component components, and the required components are available from the local electronics market. The printed board I provide is for reference only. The only principle is to make the on-off detector into a pen type for easy carrying.
If there are no conditions, the components can be directly soldered to the universal board, and the effect is the same. This circuit turns on and off the detector, not only is the principle simple to make, but also very simple, as long as the welding is correct, it can be successful without debugging.
Finally, the audio signal amplifier of the circuit continuity detector is placed in a used whiteboard pen and fixed, and the probe is taken out from the refill. The audio signal generator can be placed in an 80mm x 25mm self-made small box, and the alligator clip is taken from one end of the small box. The battery is loaded and the entire production is completed.
Fourth, the use of methods and precautions
Press the switch K before use to give the audio signal generator a trigger signal so that it emits an audio signal, then clamp the end of the line with the alligator clip, and finally touch the other end of the line with the probe of the audio amplifier. If the circuit has no open circuit failure, the music audio signal generated by the audio signal generator will be transmitted to the other end of the line through the line, and the audio amplifier will receive a wonderful music when it receives the signal. Conversely, if there is an open circuit fault in the circuit, the audio signal amplifier will not emit a musical sound, or only a small noise.
Special attention is given to this detector pair detection 1OOm
The line within is very effective, and the correct rate can reach 100% when the operation is correct. However, if the line under test exceeds this range, or if the bypass of the line is particularly complicated, its correct rate will decrease, so it should be noted in actual use.
When making an audio signal amplifier, the grounding end of the circuit should be taken out and made on the outer casing, which is in contact with the human hand during use, which can increase the volume of the speaker and increase the sensitivity of the detector.
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