Heater program design and development

1. Brief introduction of portable heater

With the progress of the times, people's living standards have also been significantly improved. In the cold winter, people could only burn coal in their own homes for heating, which had a certain impact on people's respiratory health. The temperature inside the house was sometimes relatively high. low. In modern times, there are many heating methods. People can feel the warm temperature inside the house as long as they pay the heating fee, and it has no effect on their own health. However, it is inevitable that the heating effect is not satisfactory. Therefore, heaters have been developed to help people through the cold winter. Portable heaters are small in size, light in weight, easy to use, and are well received by consumers.

Second, the classification of portable heaters

There are six main types of portable heaters: pocket heaters, rechargeable hot water bottles, oil-filled electric heaters, PTC heaters, convection heaters, and electric film heaters.

(1) Huailu: What is Huailu? It sounds like it will only appear in yellowed books. The hand warmer, also known as the hand warmer, is the smallest portable heater. It is suitable for people with hands and feet, neuralgia, colds, rheumatism and backaches. The furnace mainly relies on the burning of oil to generate heat. The furnace body is used as a container for storing oil. Some high-quality furnaces with two or two oils can be used for 8 hours without cooling, but you must be careful to prevent oil leakage during use.

(2) Rechargeable hot water bottle: In the past, people relied on hot water bags for heating. Fill the hot water bag with boiling water and put it into the bed before going to bed every day to make the bed warmer without the cold touch. The invention of the rechargeable hot water bottle solves the shortcomings of ordinary hot water bags that have short heat preservation time and rely on boiling water for heating. The rechargeable hot water bottle mainly uses electric heating wire heating as the main control method, but if the electric heating wire hot water bottle does not undergo multi-layer processing, the safety of the inner tank is also prone to leakage and explosion.

(3) Oil-filled electric heaters: Oil-filled electric heaters are also called electric heaters. The volume of this kind of electric heater is not very large. It heats the surrounding new type of heat transfer oil through the heat pipe after it is energized, and dissipates the heat from the heat pipe or diffuser, thereby increasing the temperature. When the internal oil temperature reaches 85 degrees, its temperature control system will automatically cut off Power supply to prevent danger. Because the portable electric heater has a high safety factor, a long service life, and is convenient to use, it is suitable for families with elderly and children living at home. Although the oil-filled electric heater is easy to use and does not need to replace the heat transfer oil, its heat dissipation effect is not good and consumes a lot of electricity.

(4) PTC heater: PTC heater, as the name suggests, it can blow out high-temperature wind to increase the heat in the air. PTC is an abbreviation for ceramic heating element. Its temperature system uses a fan to blow air through the PTC heating element to force convection. The inside of the PTC heater is equipped with a temperature limiter, and when the tuyere is blocked, it will automatically cut off the power, and some also adopt the method of dumping and powering off. PTC heaters generally have good waterproof function, so they are more suitable for use in the bathroom. It has high safety performance, low price and high cost performance. It is a popular portable heater in modern times.

(5) Convection heater: The upper part of the convection heater is the air outlet, and the lower part is the air inlet. When the power is plugged in, the air around the heating tube is heated, and the air rises and is removed from the air outlet, while the surrounding cold air is taken from the air inlet The replenishment of the inlet and the circulation is the concept of the convection heating temperature system design. It also has a certain degree of safety. When the outlet is blocked and the temperature rises rapidly, the temperature control element will automatically power off. The noise of this kind of electric heater is very small, but the heating speed is slow.

(6) Electric film heater: The electric film heater is the most advanced portable heating technology. It uses a completely transparent electric heating film as the heat-generating material, uses a hot air duct structure inside, and adopts an enhanced convection method. The temperature rises quickly, and it can reach more than 100 degrees in 3 minutes. Electric film heaters are generally small in size, long in service life, novel in shape, and one of the best-selling portable heaters.

3. Design of temperature control system for portable heater

The temperature control systems of portable heaters can be divided into the following categories.

(1) Electric heating wire heating element: the heating wire is used to generate heat, and the generated heat is radiated through the fan, which is mainly used in the heater. After the product upgrade and reform, some portable electric heaters use reflective distance to dissipate the heat generated by the heating wire. Generally, the body can be rotated at a certain angle for multi-directional heating. At the same time, it also has advanced safety performance. Adopt a temperature control system that automatically cuts off the power supply when it is dumped or when the temperature is too high.

(2) Quartz tube heating element: This type of product is composed of basic components such as a sealed electric heating element, a parabolic surface or reflector, and a protective strip. The quartz radiant tube is the main temperature control element, and the energy-saving technology is heated by far infrared rays. The infrared radiation emitted by the infrared radiation can be absorbed by the object and directly turned into heat to achieve the purpose of heating. Because this kind of technology is very advanced, and infrared rays can produce physical therapy on the human body, it has always been one of the portable electric heaters favored by consumers.

(3) Metal tube heating element: same as heating wire heating, similar to electric fan. The principle of metal tube heating is used to dissipate the heat energy by the reflecting surface, thereby playing a role of heating. The design of this temperature control system is longer and safer than heating wires. But its shortcomings are the same as the heating wire heating, it needs continuous work, power consumption is large, and the temperature drops quickly after power failure.

(4) Halogen tube heating element: The halogen tube is a kind of luminous and heat-generating tube with closed property, with a tungsten wire in the middle, which is filled with halogen element inert gas. The halogen tube does not oxidize when heating, so it has a long service life, fast heating speed and high work efficiency.

(5) Carbon fiber heating element: It is made of carbon fiber to make a tubular heating element, which uses the heat generated by carbon fiber to diffuse on the reflecting surface to achieve the purpose of heating. This type of product generally uses a single tube for heating, which has a fast temperature rise and high efficiency. However, compared with other portable products, the current heaters using carbon fiber heating are slightly larger.

At present, there are temperature control systems such as thermal oil heating and ceramic heating on the market. Their heating principles are slightly different, and there are also certain differences in function and practical value. Consumers can choose the most practical portable heater based on their own needs.

Fourth, the design of energy-saving remote control electric heater

At present, the electric heaters used in large quantities are manually controlled, with high power and high energy consumption. The energy-saving remote control electric heater introduced in this article is controlled by infrared remote control, and several preset temperature values are set according to user requirements. When the room temperature during heating reaches the preset temperature, the power will be cut off automatically, and it will be heated again after the temperature drops, so as to achieve the effect of energy saving and comfort. The control system is composed of power supply circuit, main control circuit, remote control transmitter circuit, single threshold temperature control circuit, fan and residual heat dissipation protection circuit. The complete circuit is shown in Figure 1.

4.1 Power supply circuit of electric heater

After the 220V power supply voltage is dropped by the transformer, it is bridge rectified by D1-D4, filtered by C1 to generate a voltage of about 19V, and then regulated by the N3 (7812) three-terminal regulator to obtain 12V voltage, C2 filter, and Zener diode The voltage regulation value of D20 is 5.6V. Since the voltage between the emitter of the transistor V1 and the base is about 0.6~0.7V, the voltage drop between the anode of D5 and the emitter of V1 is 5V. After the C3 and C4 The first level of filtering, R3, C5 and the second level of filtering are supplied to the main chip N1, R4, C6 and the second level of filtering is supplied to the receiving head Z1. It is worth noting that the 5V power supply of N1 and Z1 are both floating power supply, which means that the negative terminal is not connected to the ground of the power supply, but the negative terminal 2 pin is connected to 7V, the positive terminal 5 pin is connected to 12V, and the voltage difference is 5V. 5V power supply.

4.2 Main control circuit of energy-saving heater

This circuit mainly adopts PT2128A-C31 integrated chip to control. C7, C8, X1, and N1 form a 455KHZ crystal oscillator to generate the clock signal required for chip operation. The receiving head Z1 receives the signal from the infrared remote control transmitter, amplifies, demodulates, and decodes it and sends it to pin 1 of PT2128A-C31. According to the information of the temperature preset value in the infrared remote control signal, pins 16 and 17 of PT2128A-C31 One of the 18 pins must be low level, and the other two pins are high level. When pin 18 is at low level, through resistor R6, the transistor V3 is saturated and turned on, its saturation voltage drop is 0.3V, and the diode D10 conduction voltage drop is 0.7V, so the negative voltage of D10 is 11V, divided by R9 and R15 Send it to the eponymous end of LM324 with 10 feet. In the same way, when pin 17 is low level, the transistor V4 is saturated and conducted through the resistor R7, and then the voltage drop through the diode D11 is sent to pin 10 of the LM324 through the partial pressure of R10 and R15. When pin 16 outputs a low level, through R8, the transistor V5 is saturated and turned on, and the voltage is reduced by diode D12, and then sent to pin 10 of LM324 through R11 and R15. These three voltages are the reference voltages for temperature settings.

When two sets of heating plates are required to heat together, the receiving head Z1 receives the infrared signal and sends it to pin 1 of the integrated block PT2128A-C31 after amplifying, demodulating and decoding. Pin 10 of PT2128A-C31 outputs low level, and the transistor V6 is made through R13. Saturation is turned on, relay J2 is closed, and PTC2 is energized and heated.

D6, D7, and D8 form an AND gate circuit. As long as one of the outputs is low, V2 will be turned on, J3 will have current, the switch will be closed, and the fan will rotate to send out the heat of the PTC heating element in the heating state , Blow out hot air.

Whenever pin 1 of PT2128A-C31 receives an instruction from Z1 and its pin 6 outputs a low level, the buzzer L1 will beep once.

4.3 Remote control transmitter circuit of heater

The infrared remote control transmitter is composed of PT2268 integrated circuit. The transmitted signal is transmitted through the D2 infrared light-emitting diode SE303 to transmit the coded signal. Each transmission is twice, one of which is inverted to prevent the receiver from receiving the wrong code. The infrared remote control transmitter circuit is shown in Figure 2.

4.4 Energy-saving heater single-threshold temperature control circuit

This circuit is mainly composed of temperature sampling circuit and comparison control circuit. The temperature sampling circuit is mainly composed of R16 and R17, among which R17 is a negative temperature coefficient thermistor, which is installed at the air inlet of the heater to sample the indoor temperature.

The comparison circuit is composed of LM324. After the indoor preset temperature is set for the heater, the 10 pin of LM324 sets a reference voltage accordingly. The sampling voltage generated by the sampling circuit is sent to pin 9 of LM324. When the indoor temperature does not reach the set temperature, the voltage of pin 10 of LM324 is greater than that of pin 9, so pin 8 outputs high level, pin 5 and pin 3 output fixed voltage. Level 5.5V, so pin 7 outputs low level and pin 1 outputs high level. The fourth op amp is connected as an emitter follower, so pin 14 also outputs a high level. At this time, the transistor V7 is turned on, the relay J1 is closed, and the heating plate starts to heat. When the indoor temperature reaches the set temperature, the voltage of pin 10 of LM324 is less than that of pin 9, and the output of pin 14 is low, the transistor V7 is cut off, the relay is disconnected, and the heating plate stops heating. But when the temperature drops slightly, the comparator flips, the relay pulls in, and the heating plate starts heating again. When the temperature reaches the set temperature, the comparator flips again, the relay is disconnected, and the heating plate stops heating. The relay keeps beating in such a short period of time and is easily damaged. To this end, an RC delay circuit composed of R20 and C9 is set up. First, the time required for the temperature in the room to drop by 2 degrees is tested through experiments, and then the resistance and capacitance are selected according to the time, and the RC delay circuit is designed. The temperature control is converted to the time control, so that when the indoor temperature is lower than the set temperature by 2 degrees, the comparator will flip and the relay will start to jump, thereby reducing the frequency of the relay jumping and ensuring the relay The working life of the unit has realized single-threshold temperature control.

4.5 The fan and the residual heat dissipation protection circuit of the electric heater

When the receiving head receives the power-on signal, one of the pins 16, 17, and 18 of the main chip is converted from high to low. Through the AND circuit, the base of the transistor V2 is low, and V2 is saturated and turned on. The relay is closed, so that the fan starts to work. When the connector receives the shutdown signal, the pins 16, 17, and 18 of the main chip are all high, and the V2 base of the triode is extremely high through the AND circuit, the triode is in the off state, the relay is disconnected, and the fan stops working.

Diodes D6, D7, D8 and resistor R5 form an AND gate circuit, so that when the heater is running at any of the low, medium, and high temperatures, the AND gate circuit outputs low level to ensure the correct operation and operation of the fan circuit . The diode D9 is to protect the transistor V2, because when the transistor V2 changes from on to off, the current flowing through the relay coil will quickly decrease from the maximum value to zero. Due to the sudden change of the current, the coil will have a high self-inductance. The electromotive force is superimposed on the power supply voltage between the C and E levels of the transistor V2, which may cause the transistor to break down. After the diode D9 is connected in parallel, the self-induced electromotive force of the coil can be clamped at the forward voltage of the diode to avoid the breakdown. Wear a diode.

The residual heat dissipation protection circuit uses the RC delay circuit to delay the shutdown of the fan, so that the fan can continue to work for a period of time after the heater is turned off, and dissipate the heat of the heater and the nearby plastics to prevent them from overheating. damage. When the receiving head receives the shutdown signal, the three pins of the main chip 16, 17, and 18 all turn from low level to high level, and because the voltage at both ends of C10 cannot change suddenly, it is considered low level, so the base of the transistor V2 It is still low level, and the transistor V2 is still conducting, so that the relay J3 is still closed, and the fan continues to rotate, so as to dissipate heat for the heating plate of the heater. At this time, the 12V voltage of the emitter of the triode charges C10 through the E and B poles of the triode V2 and the resistor R22. When the capacitor C10 is fully charged, the triode V2 is cut off, the relay is disconnected, and the fan stops working. The length of the fan's delayed operation is determined by the time constant of resistor R22 and capacitor C10. Changing the value of capacitor C10 or resistor R22 can change the length of the delay time. Increasing the value of capacitor C10 and resistor R22 will make the delay time longer. Otherwise, the delay time becomes shorter.

to sum up

The energy-saving remote control electric heater is designed with automatic temperature control and protection system, which is suitable for the upgrading of ordinary electric heaters. The temperature automatic control system is set by the remote control transmitter to control the temperature. The sensor samples and compares with the set value, analyzes, and determines the working state of the heater, which is different from the traditional dual-threshold control circuit. The system adopts single threshold value judgment and temperature-time conversion circuit to realize, optimize and simplify the circuit. The fan automatic delay protection function of the protection system has a novel, simple and convenient design idea. The whole machine has low cost, complete functions, and high performance-price ratio. Has high practical value.

In my country, the market for small home appliances has begun to take shape, and consumers' demand for portable heaters has increased significantly. Therefore, it is necessary to strengthen innovation and research on portable heaters to produce safer, more effective, convenient and faster heating products.