Constant-temperature heating control circuit

Abstract

The utility model relates to a constant-temperature heating control circuit, which comprises a main control chip, a temperature sensor reference voltage acquisition expansion circuit, a temperature sensor signal acquisition circuit, a monostable protection circuit and a heater control circuit, the main control chip, the temperature sensor reference voltage acquisition expansion circuit and the temperature sensor signal acquisition circuit are connected in sequence; the main control chip, the monostable protection circuit and the heater control circuit are connected in sequence; the temperature sensor signal acquisition circuit is connected with a temperature sensor in financial equipment; and the heater control circuit is connected with a heating device in the financial equipment.

Description

Technical Field

[0001] This utility model relates to the field of constant temperature heating control technology for financial equipment, and in particular to a constant temperature heating control circuit. Background Technology

[0002] Adjustable temperature control technology is widely used in real life, especially in the heating modules of bundling machines and banknote binding machines in financial equipment. The industry mostly adopts the instantaneous high current rapid heating method, which is affected by factors such as changes in ambient temperature, fluctuations in power supply voltage, and poor compatibility of consumables from different manufacturers, resulting in poor working stability. At the same time, financial equipment is used by major banks and requires high accuracy.

[0003] Financial equipment, such as banknote bundling machines, requires multi-point heating and cutting. Each heating point needs a corresponding set of heater assemblies. Existing heating control circuits cannot individually control each set of heater assemblies, leading to unstable heating operation. Especially when the number of heater assemblies changes, the existing circuit cannot be expanded, requiring redesign, which is time-consuming and labor-intensive, and cannot meet the needs of financial equipment. Utility Model Content

[0004] To address the shortcomings of existing technologies, this utility model provides a constant temperature heating control circuit that can achieve independent closed-loop control of multiple constant temperature heaters, with stable operation and strong practicality.

[0005] The technical solution adopted by this utility model to achieve the above objectives is: a constant temperature heating control circuit, including a main control chip, a temperature sensor reference voltage acquisition extension circuit, a temperature sensor signal acquisition circuit, a monostable protection circuit, and a heater control circuit;

[0006] The main control chip, the temperature sensor reference voltage acquisition extension circuit, and the temperature sensor signal acquisition circuit are connected in sequence; the main control chip, the monostable protection circuit, and the heater control circuit are connected in sequence;

[0007] The temperature sensor signal acquisition circuit is connected to the temperature sensor in the financial equipment; the heater control circuit is connected to the heating device in the financial equipment.

[0008] The temperature sensor reference voltage acquisition expansion circuit uses a first operational amplifier and a multiplexer chip.

[0009] The inverting input terminal of the first operational amplifier is connected to the output terminal, and the non-inverting input terminal is connected to the digital-to-analog converter output terminal DS0 of the main control chip through resistor R46;

[0010] The output terminal of the first operational amplifier is connected to the input terminal of the multiplexer chip; a certain output terminal of the multiplexer chip is connected to the temperature sensor signal acquisition circuit.

[0011] The enable terminal and three address selection terminals of the multiplexer are connected to the power supply via resistors.

[0012] The temperature sensor signal acquisition circuit employs a second operational amplifier and a third operational amplifier.

[0013] The positive input terminal of the second operational amplifier is connected to the temperature sensor in the financial equipment and is also connected to the power supply through resistor R62. The inverting input terminal is connected to the output terminal, and the output terminal is connected to the inverting input terminal of the third operational amplifier through resistor R51.

[0014] The positive input terminal of the third operational amplifier is connected to one of the output terminals of the multiplexer chip in the temperature sensor reference voltage acquisition expansion circuit, and the positive input terminal is grounded through capacitor C7; the output terminal of the third operational amplifier is connected to the inverting input terminal of the third operational amplifier through resistor R52 and is also grounded through capacitor C8; the output terminal of the third operational amplifier is connected to the analog input terminal of the main control chip through resistor R59.

[0015] There are multiple temperature sensor reference voltage acquisition expansion circuits and multiple temperature sensor signal acquisition circuits.

[0016] The monostable protection circuit uses a transistor and a dual monostable trigger.

[0017] The base of the transistor is connected to the output terminal of the main control chip through resistor R42, and the base is connected to the power supply in sequence through resistors R42 and R35, while the emitter is grounded; the collector of the transistor is connected to the power supply through resistors R36 and R37, and the collector is connected to the reset input terminal of the dual monostable multivibrator.

[0018] The reset input terminal of the dual monostable multivibrator is connected to the rising edge trigger input terminal TR+, and the falling edge trigger input terminal TR- is grounded; the inverting output terminal of the dual monostable multivibrator... It is connected to the power supply via resistor R39 and to the heater control circuit via resistor R43.

[0019] The heater control circuit uses an H-bridge control chip; the inverting control input terminal RINB of the H-bridge control chip is connected to a monostable protection circuit; the inverting control input terminal RINB and the forward control input terminal FINB of the H-bridge control chip are respectively connected to the power supply through resistors; the two output terminals of the H-bridge control chip are connected to the heating device in the financial equipment.

[0020] An indicator light is also connected between the two output terminals of the H-bridge control chip. Multiple monostable protection circuits and heater control circuits are used. The temperature sensor is a PT100 resistance temperature detector (RTD).

[0021] This utility model has the following beneficial effects and advantages:

[0022] 1. This utility model adopts a main control chip, a temperature sensor reference voltage acquisition extension circuit, a temperature sensor signal acquisition circuit, a monostable protection circuit, and a heater control circuit. Through constant temperature heating, multiple heating modules (monostable protection circuit and heater control circuit) can acquire and control the temperature according to the set temperature value to achieve closed-loop control and temperature stability. In practical applications, such as banknote bundling machines in the financial field, five-point heating and bonding cutting equipment needs to achieve five-point heating and bonding cutting. Each bonding and cutting heating point requires a corresponding set of heater components. Each set can be individually set to control the temperature to ensure reliable and stable operation.

[0023] 2. This utility model employs multiple temperature sensor reference voltage acquisition extension circuits and temperature sensor signal acquisition circuits, and can select the output path through a multi-way switch to achieve closed-loop control of a single heating group.

[0024] 3. This utility model adopts a monostable protection circuit and a heater control circuit to protect the heating operation and increase the stability of the entire circuit. Attached Figure Description

[0025] Figure 1 This is the pin diagram of the main control chip of this utility model;

[0026] Figure 2 This is a circuit diagram for acquiring the reference voltage of a temperature sensor.

[0027] Figure 3 This is a circuit diagram for acquiring signals from a temperature sensor.

[0028] Figure 4 This is a monostable protection circuit diagram;

[0029] Figure 5 This is the heater control circuit diagram.

[0030] Figure 6 This is a schematic diagram of the working principle of this utility model. Detailed Implementation

[0031] The present invention will now be described in further detail with reference to the accompanying drawings and embodiments.

[0032] This invention discloses an extended constant-temperature heating control circuit for controlling the constant temperature of heater assemblies. It includes: a main control chip, a temperature sensor reference voltage acquisition extension circuit, a temperature sensor signal acquisition circuit, a monostable protection circuit, and a heater control circuit, enabling closed-loop constant-temperature control of multiple heaters in the equipment. The temperature sensor signal acquisition circuit is connected to the temperature sensor in the heater assembly of the financial equipment, and the heater control circuit is connected to the heating device in the heater assembly. Multiple heater assemblies can be configured as needed. Taking a banknote bundling machine as an example, to achieve five-point adhesion and cutting, there are three heater assemblies at the top of the machine and two heater assemblies at the bottom.

[0033] like Figure 1 As shown, the main control chip is the C8051F120 microcontroller.

[0034] like Figure 2 As shown, in the temperature sensor reference voltage acquisition expansion circuit, the output terminal DS0 of the microcontroller's internal digital-to-analog converter is connected to the input terminal of operational amplifier U9A through resistor R46. The output terminal of operational amplifier U9A is connected to the input terminal of multiplexer U8, and the multiplexer selects the temperature sensor signal acquisition circuit of each group of heaters to provide a reference voltage. Operational amplifier U9A is connected as a voltage follower circuit, serving the functions of buffering, isolation, and improving load capacity. The microcontroller controls the three address selection terminals KGXZA, KGXZB, and KGXZC of multiplexer U8 to select eight switch output paths. FINHA is the enable signal for the microcontroller to control the multiplexer. The enable terminal and the three address selection terminals of the multiplexer are connected to the power supply through resistor array RP1 to provide anti-interference.

[0035] like Figure 3 As mentioned above, taking the multiplexer selection 1DA0 as an example, the temperature sensor signal acquisition circuit adopts a two-stage operational amplifier circuit. The first-stage heater temperature sensor acquisition signal WDCJ0 is input through the positive input terminal of operational amplifier U13B, and the inverted input terminal of U13B is connected to its output terminal.

[0036] The U13B is a voltage follower, serving as a buffer, isolator, and improves load capacity. The heater temperature sensor WDCJ0 collects signals and is connected to the power supply via resistor R62 at the top and to socket P2 at the bottom. Pins 1 and 2 of socket P2 are connected to the heater. When the heater assembly temperature changes, the corresponding temperature sensor resistance changes. The heater and resistor R62 are connected in series with the power supply and ground. The change in heater resistance and the voltage division by R62 result in different voltage values ​​corresponding to different temperatures. The higher the heater temperature, the higher the temperature sensor resistance, and the higher the corresponding output voltage. The resistance value of resistor R62 is chosen to be close to the resistance value of the heater at room temperature.

[0037] The second stage, U13A, uses a dual-input mode. IDA0 is connected to the positive input terminal of the operational amplifier to provide a reference voltage, while the inverting input terminal is connected to resistors R51 and R52 respectively. The output signal of U13A is connected to the analog-to-digital converter input terminal AIN0 of the microcontroller through resistor R59. The output voltage of AIN0 is approximately equal to the output voltage of the first stage plus twice the voltage of IDA0.

[0038] like Figure 4 As shown, the monostable protection circuit uses a 74HC221 chip. Its pin 1, the falling edge trigger input, is connected to the power supply ground. Its pin 2, the rising edge trigger input, and its pin 3, the external reset input, are connected to the collector of transistor T5, resistor R39, and resistor R37. The pin 4, the inverting output of the 74HC221 chip, is connected to the input of the H-bridge control chip U2 through resistor R43.

[0039] Based on the collected data, the microcontroller compares the temperature setpoint and outputs a control signal. This signal is connected via resistor R42 to transistor T5, which is then connected to the input of dual monostable multivibrator U7. The output of U7 is connected via resistor R43 to the input of the H-bridge control chip U2. A monostable multivibrator protection circuit is used to prevent the microcontroller from abnormally controlling the heater for extended periods in case of program crashes or freezes. The maximum single-operation time T of the microcontroller is limited. w =0.7CR, where C is the capacitance value of the monostable circuit, i.e., C5 in the figure, and R is the resistance value of the monostable circuit connected to the power supply pin, i.e., R38 in the figure.

[0040] Because the microcontroller's I / O ports default to a high-level state upon power-up, the soldering iron must be set to operate at a low level to prevent abnormal operation during power-up. A transistor T5 is added to achieve level switching. When RIN7 outputs a low level, transistor T5 is cut off. The collector of T5 is connected to pin 2 (rising edge trigger input) and pin 3 (external reset input) of the monostable multivibrator 74HC221, resulting in a high level. At this time, pin 4 (inverting output) of the 74HC221 chip outputs a falling edge pulse waveform. The maximum low-level duration is determined by resistor R38 and capacitor C5. Under normal microcontroller operation, RIN7 outputs a high level for 0.1ms within the maximum operating time, triggering transistor T5 to conduct. At this time, pin 2 (rising edge trigger input) and pin 3 (external reset input) of the 74HC221 are low, forcibly terminating the pulse output from pin 4 of the 74HC221. The output then returns to a high level, completing the reset. The microcontroller then cycles through high and low levels until the set temperature is reached.

[0041] Conversely, if the microcontroller exceeds its maximum operating time under abnormal conditions, the 74HC221 chip will output an abnormal high level at pin 4 and stop working. It will only return to normal operation when the rising edge trigger input at pin 2 and the external reset input at pin 3 of the 74HC221 are both at a low level.

[0042] like Figure 5 As shown, the heater control circuit uses an H-bridge control chip to control whether the heater is heating. The FIN7 positive control input and RIN7- negative control input are connected to the power supply through the RP2 resistor array. The RP2 pull-up resistor has an anti-interference function. For example, when the heater needs to work, the RIN7- terminal gets a low level, and the FIN7 terminal remains at a high level. The output terminals SZLTZZ and SZLTZF will provide a 24V working voltage for the heater. Conversely, when the heater is not working, both the RIN7- terminal and the FIN7 terminal are at a high level. D4, R27, D3, and R28 are working status indicator lights. F1 and F2 are self-resetting fuses to stop heating in case of internal short circuit of the heater. The output terminal of U2 is connected to the socket P1 to connect to the external heater.

[0043] like Figure 6 As shown, the workflow of this utility model is as follows:

[0044] Depending on the scenario or the consumables used, the constant temperature value of each group of heaters can be set separately on the display screen. At the same time, the reference level of the microcontroller output terminal DS0 is connected to the reference voltage acquisition expansion circuit of the control temperature sensor through the digital-to-analog converter output terminal U9A. It is connected through resistor R46. The microcontroller I / O output terminal is connected to the three address selection terminals KGXZA, KGXZB, and KGXZC of the U8 multiplexer, respectively, and the multiplexer enable signal terminal FINHA. The microcontroller controls and selects 8 switch output paths per unit time. For the 8 switch output paths of the multiplexer, the microcontroller's digital-to-analog converter output terminal DS0 can output 8 sets of reference voltages per unit time.

[0045] Taking the multiplexer 1DA0 as an example, it provides a reference voltage to the temperature sensor 1 signal acquisition circuit. WDCJ0 in the temperature sensor 1 signal acquisition circuit is connected to the temperature sensor via the input of operational amplifier U13B, and is connected to resistor R62 and socket P2 respectively. The other end of R62 is connected to the power supply, and the two ends of P2 are connected to the two pins of the temperature sensor respectively. The positive input of operational amplifier U13B obtains the voltage value corresponding to the current temperature through voltage division between the internal resistance of the temperature sensor and resistor R62. The inverting input and output of operational amplifier U13B are connected to resistor R51. The inverting input of operational amplifier U13A is connected to resistors R51 and R52 respectively. The output of operational amplifier U13A is connected to resistor R52, resistor R59, and capacitor C8 respectively. When the temperature sensor senses a temperature change, the sensor's internal resistance changes, the voltage at the positive input of operational amplifier U13B changes, and the output of U13B follows the voltage change. The output of U13A is connected to resistor R59 through resistor R59. When the voltage at AIN0 changes, the microcontroller's analog-to-digital converter input AIN0 receives the voltage change and compares it with the set temperature value. If the set temperature has not been reached, the microcontroller outputs a low-level signal connected to resistors R42 and R35 in the monostable protection circuit. At this time, transistor T5 is cut off, and the high-level collector of the transistor is connected to resistors R36 and R37, pin 2 of the rising edge trigger input of U7, and pin 3 of the external reset input. Then, pin 4 of the inverting output of U8 outputs a falling edge pulse waveform, the maximum duration of which is determined by resistor R38 and capacitor C5. Under normal operating conditions, the microcontroller will output a low-level signal for a shorter time than the falling edge pulse waveform output at pin 4 of the inverting output of U8. The microcontroller will output a high level for 0.1ms, forcibly terminating the 74HC221 pulse output, and then output a reset high level at pin 4. After resetting, the microcontroller will again output a low level, cycling between high and low levels until the set temperature is reached.

[0046] Conversely, if the microcontroller exceeds its maximum operating time under abnormal conditions, the 74HC221 chip will output an abnormal high level at pin 4 and stop working. It will only return to normal operation when the rising edge trigger input at pin 2 and the external reset input at pin 3 of the 74HC221 are both at a low level.

[0047] Pin 4 of the inverted output of U7 is connected to the inverted control input RIN7- of the heater 1 control circuit U2 through resistor R42. When RIN7- is low, FIN7 remains high, and the output terminals SZLTZZ and SZLTZF provide a 24V operating voltage to the heater, thus heating the heater.

[0048] The microcontroller's analog-to-digital converter input terminal AIN0 receives the voltage change and compares it with the set temperature value. When the set temperature is reached, the microcontroller outputs a high-level signal, and pin 4 of the 74HC221 chip outputs a high level. The RIN7- and FIN7 terminals of U2 are connected to the power supply through the pull-up resistor array RP2 and are both at a high level, so the heater does not heat up.

Claims

1. A thermostatic heating control circuit, characterized by, It includes a main control chip, a temperature sensor reference voltage acquisition extension circuit, a temperature sensor signal acquisition circuit, a monostable protection circuit, and a heater control circuit; The main control chip, the temperature sensor reference voltage acquisition extension circuit, and the temperature sensor signal acquisition circuit are connected in sequence; the main control chip, the monostable protection circuit, and the heater control circuit are connected in sequence. The temperature sensor signal acquisition circuit is connected to the temperature sensor in the financial equipment; the heater control circuit is connected to the heating device in the financial equipment.

2. A thermostatic heating control circuit according to claim 1, wherein The temperature sensor reference voltage acquisition expansion circuit uses a first operational amplifier and a multiplexer chip. The inverting input terminal of the first operational amplifier is connected to the output terminal, and the non-inverting input terminal is connected to the digital-to-analog converter output terminal DS0 of the main control chip through resistor R46; The output terminal of the first operational amplifier is connected to the input terminal of the multiplexer chip; a certain output terminal of the multiplexer chip is connected to the temperature sensor signal acquisition circuit. The enable terminal and three address selection terminals of the multiplexer are connected to the power supply via resistors.

3. A thermostatic heating control circuit according to claim 1, wherein The temperature sensor signal acquisition circuit employs a second operational amplifier and a third operational amplifier. The positive input terminal of the second operational amplifier is connected to the temperature sensor in the financial equipment and is also connected to the power supply through resistor R62. The inverting input terminal is connected to the output terminal, and the output terminal is connected to the inverting input terminal of the third operational amplifier through resistor R51. The positive input terminal of the third operational amplifier is connected to one of the output terminals of the multiplexer chip in the temperature sensor reference voltage acquisition expansion circuit, and the positive input terminal is grounded through capacitor C7; the output terminal of the third operational amplifier is connected to the inverting input terminal of the third operational amplifier through resistor R52 and is also grounded through capacitor C8; the output terminal of the third operational amplifier is connected to the analog input terminal of the main control chip through resistor R59.

4. A thermostatic heating control circuit according to any one of claims 1 to 3, wherein There are multiple temperature sensor reference voltage acquisition expansion circuits and multiple temperature sensor signal acquisition circuits.

5. The constant temperature heating control circuit according to claim 1, wherein The monostable protection circuit uses a transistor and a dual monostable trigger. The base of the transistor is connected to the output terminal of the main control chip through resistor R42, and the base is connected to the power supply in sequence through resistors R42 and R35, while the emitter is grounded; the collector of the transistor is connected to the power supply through resistors R36 and R37, and the collector is connected to the reset input terminal of the dual monostable multivibrator. The reset input end of the double monostable trigger is grounded with the rising edge trigger input end TR+ and the falling edge trigger input end TR-; the reverse output end of the double monostable trigger is connected with the input end of the first D flip-flop The resistor R39 is connected with the power supply and also connected with the heater control circuit through the resistor R43.

6. A thermostatic heating control circuit according to claim 1, wherein The heater control circuit uses an H-bridge control chip; The inverting control input terminal RINB of the H-bridge control chip is connected to a monostable protection circuit; the inverting control input terminal RINB and the forward control input terminal FINB of the H-bridge control chip are respectively connected to the power supply through resistors; the two output terminals of the H-bridge control chip are connected to the heating device in the financial equipment.

7. A thermostatic heating control circuit according to claim 6, wherein In the heater control circuit, an indicator light is also connected between the two output terminals of the H-bridge control chip.

8. A thermostatic heating control circuit according to any one of claims 1, 5, 6, wherein, There are multiple monostable protection circuits and heater control circuits.

9. The constant temperature heating control circuit of claim 1, wherein, The temperature sensor is a PT100 resistance temperature detector (RTD).

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