Abstract: The "Automatic Newspaper Holder" is a product independently developed by the author. This paper mainly describes how the automatic control of the newspaper holder is achieved by utilizing inductive sensor technology combined with analog and digital electronic circuits. Keywords: Inductive sensor; newspaper holder; automatic control I. Introduction With the development of society and the rapid advancement of information technology, related industries have sprung up like mushrooms after rain. Sensor technology has also grown alongside the development of information technology, demonstrating its charm and style in many fields such as industrial automation, national defense, bioengineering, and transportation. It works in conjunction with electronic circuits to achieve intelligent automatic control. The "Automatic Newspaper Holder" designed in this paper can realize automatic newspaper clipping and automatic newspaper storage and retrieval. The device mainly consists of two parts: a mechanical transmission system and a circuit control system. It has the functions of storing seven newspaper clips, automatic newspaper clipping, and intelligent automatic newspaper clip selection. II. Circuit Composition The automatic newspaper clip storage and retrieval control circuit mainly consists of an inductive sensor, a counter, an encoder, a comparator, a decoder driver, and a digital display. The principle block diagram is shown in Figure 1, and the circuit diagram is shown in Figure 2. 1. Inductive Sensor: An inductive sensor is a non-contact detection device. Its internal structure, as shown in Figure 3, consists of a high-frequency oscillator, detector, amplifier, trigger, and output circuit. The high-frequency oscillator generates an alternating electromagnetic field at the sensor's detection surface. When a metal object approaches the sensor's detection surface, the eddy currents generated in the metal absorb the oscillator's energy, weakening or even stopping the oscillation. These two states—oscillation and cessation—are converted into electrical signals, which are then shaped, amplified, and converted into binary switching signals. After power amplification, the output is either high or low level. Specifically, when the newspaper clip approaches the inductive sensor's detection surface, the sensor output is high (power supply voltage 24V); when the newspaper clip deviates from the sensor's detection surface, the inductive sensor output is low (0V). 2. The control circuits S1-S7 form a keypad, representing seven different newspaper clips in the newspaper compartment. This keypad is a decimal number, which is encoded into a four-digit hexadecimal number by encoder U1 (74LS147). The hexadecimal number is output from pins 14, 9, 7, and 6 of U1, and then amplified by inverter U2 (74LS04). The signal is then split into two outputs: one is sent to decoder/driver circuit U3 (74LS48), which decodes it into a decimal number that the digital tube can recognize and drives the digital tube to display the decimal number pressed on the keypad; the other is sent to comparator U4 (74LS85) as reference data for comparison with the data acquired by the inductor sensor. When the newspaper clip passes the inductive sensor, the pulse generated by the sensor is sent to counter U6 (CD4518) for counting. U6 then translates this pulse into a four-digit hexadecimal number, which is output as two signals. One signal is sent to comparator U4 for data comparison. When the two input signals are equal, pin 6 of comparator U4 outputs a high level, which, via R1, saturates and turns on Q7. J6 and J7 then control the motor to stop. The other signal, along with the detection signal from the motor control circuit J6, simultaneously enters the logic control circuit U5 (74LS08) for logic condition detection and judgment. When the count pulse is 7 and J6 is activated, the logic circuit outputs a high-level signal, commanding the reset circuit to reset the counter for 2 seconds. The specific operation is as follows: (1) When the number pressed on the keyboard is less than "7" and the counter count is also less than "7", for example, when the key press is "5", the encoded DCBA is 1010, and the inverted DCBA is 0101. One signal is sent to the decoding drive circuit for 4-7 line decoding and drives the common cathode digital tube to display "5"; the other signal enters the comparator. At this time, the inductor sensor detects the pulse of the newspaper clip, counts it through the counter and sends it to the comparator. The comparator compares the two signals. When the counter output is not equal to "5", the comparator OA=B is at a low level, Q1 is cut off, J6 is not energized, J7 is energized, and 220V power is applied to the motor through J7, and the motor continues to run. When the number of pulses output by the counter is equal to "5", the comparator OA=B is at a high level, Q1 is turned on, J6 is energized, its normally closed contact is open, J7 is not energized, the normally open contact is open, and the motor stops. (2) When the keypad and counter output states are both equal to 7, comparator OA=B is at a high level, Q1 is turned on, J6 is energized, its normally closed contact opens J7, J7 is not energized, its normally open contact opens, and the motor stops. At this time, if any key on the keypad other than 7 is pressed, comparator OA=B is at a low level, Q1 is cut off, J6 does not operate, its normally closed contact closes, J7 is energized, the normally open contact of J7 connects the power supply, and the motor runs. At this time, since the counter outputs "7", pins ① and ② of U5A are at a high level, pin ③ outputs a high level, pin ④ of U5B is at a high level, pin ⑤ is also at a high level, causing pin ⑥ to output a high level, and pin ⑨ of U5C is also at a high level. Since J6 is not energized, its normally open contact is open, causing pin ⑩ of U5C to be at a high level. Therefore, pin ⑧ of U5C outputs a high level, Q2 conducts, J8 is energized, and its normally open contact closes. The +12V power supply powers the timer reset circuit via J8, which is supplied by J1 and J2. The reset circuit (Figure 4) composed of Q4, U9 (CD4541BE), etc., starts working. J1 activates, its normally closed contact opens, U6 starts resetting, and the timing circuit starts counting. When the count reaches 2 seconds (which can be achieved by adjusting R13), pin 8 of U9 outputs a high level, Q4 conducts, J2 activates, its normally closed contact opens, cutting off the power supply to the timing circuit. J1 and J2 reset, the counter reset ends, and U6 starts counting again. At this time, Q2 is cut off, J8 is not energized, and the timing circuit does not work until the counter output equals the number pressed on the keyboard, at which point the motor stops. When the keyboard and counter output states are both equal to 7, and any key other than 7 is pressed, the timing reset circuit repeats the above reset operation. 3. Power Supply Circuit The power supply circuit is shown in Figure 5. It consists of transformer, rectifier, filter, voltage regulator, and AC/DC power conversion circuits. The 220V AC power is transformed to 12V AC voltage by transformer T1, rectified by a bridge rectifier circuit composed of D1-D4, and then filtered by C1, converting the 12V AC voltage to approximately 15V DC voltage, which is then fed into the conversion circuit. The AC/DC conversion circuit mainly consists of D5, D6, D7, C1, C2, and battery BT1. When the mains power (220V) is supplied, the rectified and filtered voltage is greater than the battery voltage, so D5 and D6 conduct, and D7 is cut off. The rectified and filtered voltage supplies power to the motor control circuit and charges battery BT1. When the mains power is interrupted, the 12V DC power supply from the battery supplies power to the counter through D7 and U7 (regulated 5V), maintaining the counter's memory. To address the momentary power outage that may occur during AC/DC conversion, capacitor C2 (100uF) is added to the circuit. The discharge time of capacitor C2 is greater than the power outage time, thus maintaining power supply to the counter. III. Selection and Debugging of Main Components The inductor sensor (LV) uses the SIEN-M30B-PS-KL inductor sensor from FESTO. Since this sensor operates on a 24V power supply, U12 is added between them for voltage regulation to better connect the sensor and the counter and protect the counter. If a 5V inductor sensor is used, its output can be directly connected to pin ① of U6 (CD4518BE), omitting U12. U1 can be a 74LS147, a 10-4 line priority encoder; this circuit is only configured as a 7-4 line encoder. U2 is a hex inverter... The following components are selected: 74LS04; U3 is a 74LS48, a 4-7 segment common cathode decoder driver circuit; U4 is a four-bit data comparator, which can be a 74LS85; U5 is an AND gate circuit, which can be a 74LS08, used in the design of a condition detector; U6 can be a CD4518, a CMOS45 series product, a hexadecimal counter, configured as a pulse rising edge counter in this circuit; U9 is a CD4541BE, a programmable oscillator/counter; U7 and U12 use the AN7805 three-terminal voltage regulator IC; U8 uses the AN7812; U11 uses the AN7824. Most of these components are digital integrated circuits. When soldering integrated circuits, it is best to use IC sockets to avoid damage from static electricity from the soldering iron. During debugging, the power supply circuit should be adjusted first, followed by the control circuit. A multimeter is generally sufficient for adjusting the power supply circuit. For the control circuit, a combination of multimeter and oscilloscope is used. First, simulation (using iron to simulate the newspaper clip passing through) is used, and then actual application is carried out. The circuit design is verified step by step. Since the adjustable components of this circuit are extremely small, the circuit control effect is relatively easy to achieve. IV. Conclusion This circuit uses an inductive sensor to detect the number of pulses of the newspaper clip and uses ordinary digital integrated circuits to realize the automatic newspaper clipping and automatic selection control. This design idea and circuit design can be further improved and perfected by the developers and can also be applied to other automation fields. 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