Listened short-circuit tester ----- Short-Circuit Tester

Keywords: canned short circuit tester Listed short circuit tester This is a very simple low-cost radical tester that requires only one four-comparator chip LM339 (IC1), and several resistors and a piezoelectric buzzer can be easily produced. Circuit operating power is 9V battery. In fact, there is only one comparator in the 4 comparators to play a main role, and the other three comparators are connected to the driven power piezoelectric buzzer PZ1. The voltage composed of R1 and R2 sets the voltage of the inverting input pin 8 of the comparator A to 190 mV, and R3, the R4 fixed voltage divider sets the voltage of the same phase input foot ⑨ at 30 mV. The resistor R5 is connected between the comparator A output and the same phase input foot ⑨ to provide the necessary feedback. Reducing the bounce effect when triggering, the most effective solution is to use positive feedback to introduce a small amount of lag, this hysteresis can separate the switching point of the upper swings of the input voltage and the switching point of the hem, so that the circuit starts the switching process, the input voltage An important backhaul must be experienced before the reverse switching process occurs, so that the input voltage is swayed and uncomfortable. In standby, due to the potential (190 mV) of inverted input foot 8 above the potential (30 mV) of the same phase input foot ⑨, the comparator A is output to a low potential, and the low potential is sent to the opposite of comparator B, C, D After the phase input feet, the output of the three comparators is high, so the voltage of the piezoelectric buzzer is almost equal. The buzzer is not awkward. Be Only when the resistance connected between the two probes is less than 15 Ω, the potential of the inverted input foot 8 of the comparator A can become less than 30 mV from 190 mV. The output polarity of the comparator A is reversed. The output of parallel comparators B, C, D is low, and the piezoelectric buzzer is called, indicating that the conduction between the probe is good. The three comparator outputs a total of 50 mA currents, which is enough to make the piezoelectric buzzer. Use this tester to determine if the resistance is less than 15 Ω. If you want to be more or smaller than 15Ω, you can change the resistance of R1 to R4 to meet. Author: Zi Liang

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