Intelligent detection and control circuit of water boiler based on AT89C2051

An "intelligent detection control circuit" for the water heater is designed and manufactured using the AT89C205l single-chip computer chip. It can monitor the water level in the water tank and the working status of each group of electric heating tubes in real time. Once the water level in the water tank is abnormal or the electric heating tube fails, it can automatically complete the protection action and give the corresponding sound and light alarm signal to prompt the maintenance management personnel to carry out maintenance in time. The circuit has the advantages of simple structure, easy production and convenient use.

1. Main functions and features

(1) The circuit is simple. The entire circuit uses a "single-chip computer" chip and two auxiliary chips, and a small number of peripheral discrete components to complete the relevant control functions.

(2) When the power is initially turned on, the system will detect the water level in the water tank. Only when the water level in the water tank is normal (the water level switch SVV is closed) will the three-phase solid-state relay SSR be turned on and the electric heating tube will be powered on and work. After that, the system will monitor the water level in the water tank in a loop. Once the water level in the water tank is lower than the preset minimum water level (i.e., the automatic water supply pipe system fails), causing the SVV switch to disconnect, the system will immediately cut off the power supply to the electric heating tube and give a sound and light alarm signal of "lack of water".

(3) When the electric heating tube is powered on, the system will monitor the working status of the three groups of electric heating tubes connected to the three-phase electricity and give corresponding light-emitting tube indications on the control panel. When each group of electric heating tubes is working normally, the three groups of electric heating tube working status indicator lights on the panel will light up at the same time. If a group of electric heating tubes is damaged, the corresponding group of electric heating tube indicator lights on the panel will start to "flash", indicating that the group of electric heating tubes is faulty and needs to be repaired and replaced. However, the water boiler can still work barely at this time, but the time for the water to boil will be correspondingly extended. If two or three groups of electric heating tubes are damaged at the same time, the three groups of electric heating tube indicator lights on the panel will "flash" at the same time, and the buzzer will also emit alarm sounds of "beep, click, beep", indicating that the electric heating tubes of the water boiler can no longer work properly and must be repaired and replaced immediately.

(4) When the temperature switch WK is in the on state, it means that the water in the water tank has not yet boiled. If the water level in the water tank is normal at this time, the system will control the three-phase solid-state relay SSR to conduct, so that each group of electric heating tubes can be powered on.

At the same time, the "heating" indicator light on the panel will be lit. When WK is disconnected, it means that the water in the water tank has boiled. At this time, the "heating" indicator light on the panel will automatically go out, the "keep warm" indicator light will be lit, and each group of electric heating tubes will stop being powered on.

(5) The input and output of this circuit all adopt the working mode of photoelectric isolation, with strong anti-interference ability and stable and reliable operation.

2. Circuit principle

The circuit is shown in the figure below. The AT89C2O51 "single-chip microcomputer" chip IC1 is the core of this circuit, and C3 and R3 constitute a simple power-on automatic reset circuit. JT, C1, C2 and the related pins of IC1 constitute the clock circuit of the "single-chip computer". Only 13 of the 15 I/0 ports of IC1 are used, among which P1.1 to P1.6 are used as the output control ports of the indicator lights on the control panel. They are connected to the negative pole of an LED light-emitting diode through a current-limiting resistor respectively. The low level is effective and directly drives the LED display. P1.7 is the load (electric heating tube) control port, which is connected to the 2nd pin of the photoelectric coupler GO1 through a current-limiting resistor, and its 1st pin is connected to +5V. When P1.7 is at a high potential, GO1 and the three-phase solid-state relay are cut off, and each electric heating tube is not powered on. When P1.7 is at a low potential, GO1 and the three-phase solid-state relay are turned on, and each electric heating tube is powered on. P1.0 is the alarm signal control output port, connected to the 15th pin of IC2. The 10-14 pins of IC2 are connected to the outer ring components to form a controllable audio oscillator. Its 15th pin is the control terminal (high level is effective). The 9th pin is the output terminal. The output signal is amplified by the audio low-power amplifier composed of IC3 and then drives the speaker to make a sound. Usually, the P1,0 of the single-chip microcomputer outputs a low level under software control, and the controllable audio oscillator is in a stopped state, so there is no sound in the speaker. When the circuit needs to send out an audio alarm signal, the P1.0 of the single-chip microcomputer outputs a high level signal intermittently through software control, and the controllable audio oscillator will work intermittently, causing the speaker to emit a beep, beep, and hum alarm sound. The 1-7 pins of IC2 form a level conversion circuit for the monitoring signal of the working status of the electric heating tube. The working status sensor of the electric heating tube adopts the TAl420 type, which is a vertical, core-through (?5), and can be printed The small precision AC current transformer (HGQ1~HGQ3) directly welded and installed on the circuit board has the characteristics of fully enclosed, good mechanical and environmental resistance, strong voltage isolation ability, beautiful appearance, high precision, wide sampling range, flexible application, etc. When in use, a power lead in each group of electric heating tubes should be passed through the core hole of the current transformer corresponding to the group. In this way, when each electric heating tube works normally, AC current will pass through the power connection line of the electric heating tube passing through each current transformer. Due to the mutual inductance, a mutual inductance AC signal will be generated at the coil end of each current transformer. The signal is converted into a high-level DC signal voltage by the three groups of rectifier bridges Q1-Q3, and connected to the 2, 4, 6 (7) pins of IC2 respectively. After the high level is converted into a low level by IC2, it is output from the 1, 3, and 5 pins respectively and connected to the single Obviously, if a group of electric heating tubes does not work, the corresponding current transformer will not have an induction signal output, and IC2 and its corresponding output terminal will not have a low-level signal output. In this way, by cooperating with the software, the working status of each electric heating tube can be accurately identified and the corresponding light-emitting diodes can give corresponding indications. The DWI~DW3 voltage-stabilizing diodes mainly play a protective role, used to prevent the output signal of the current transformer from exceeding the VCC working voltage (+5V) of IC2 and causing damage to the relevant input terminals of IC2. The water level signal sensor uses a normally-on (connected when the water level is normal) float-type liquid level switch, which is connected in series in the input control circuit of GO2. The output terminal of GO2 is connected to an "inverter" circuit, which is output from pin 5 and connected to P3 of the single-chip microcomputer. ,3. By cooperating with the software, the water level status can be accurately identified and the corresponding LED can be used to give a "water shortage" alarm luminous signal. As mentioned above, the sound signal of the water shortage alarm is a discontinuous high-level signal output by the software to control the audio oscillator to work intermittently, so that the speaker can emit a beep, hum, beep alarm sound. The temperature signal sensor uses a normally-on {connected when the temperature is not reached) type temperature control switch WK with a temperature value of 980C, which is connected in series in the input control loop of GO3. The output end of GO3 is also connected to an "inverter" circuit, which is output from pin 5 and connected to P3.2 of the microcontroller. By cooperating with the software, the water temperature status can be accurately identified and the output control end can be used to control whether the electric heating tube is powered on or not, and the corresponding LED can be used to give a "heating" or "keeping warm" status indication. The power transformer T1, bridge rectifier QZ, 7805 three-terminal regulator WY and C1, C2 form a power supply circuit, which can provide a stable +5V DC working power supply for the entire circuit.

The specifications of the components required in the circuit are marked in the figure below. 3. Program Introduction This program is written in assembly language. The flow chart is shown in the figure below. After the program runs, in the initialization program, the allocation and definition of the on-chip RAM space are completed. In the main program, the state of P3.3 port must first be detected to determine whether the water tank is "lack of water". If it is "lack of water", the "lack of water" alarm control program will be immediately entered, the output control will be turned off, and the power to the electric heating tube will be stopped. Then, the sound and light alarm signal of "lack of water" will be issued to prompt inspection and repair. If it is not "lack of water", it will turn to the "temperature status" detection program to detect whether the temperature switch WK is closed. If WK has been disconnected, it means that the water has boiled, then the "keep warm" status indicator light will be directly turned on and return to continue detection. If WK has not been disconnected, it means that the water has not boiled, then the output control terminal will be immediately opened to power the electric heating tube, and at the same time, the "keep warm" status indicator light will be turned off and the "heating" status indicator light will be turned on. Then the system enters the "electric heating tube working status detection" program, and detects the sensor signals of each electric heating tube status in turn. If the sensor signal of a group of electric heating tubes disappears, it means that the group of electric heating tubes is faulty, and the corresponding working status indicator light of the electric heating tube will flash immediately. At the same time, the faulty electric heating tubes will be counted. When the number of faulty electric heating tubes is equal to or more than 2 groups, the output control will be immediately turned off to cut off the power of each electric heating tube. At the same time, the indicator lights of the working status of the three groups of electric heating tubes will flash at the same time, and intermittent audio alarm signals will be issued, indicating that the electric heating tubes need to be replaced and repaired. In order to improve the anti-interference performance of the entire circuit and prevent the program from "running away", "delayed defibrillation" and "software traps" are set in various relevant parts of the program, which can further improve the stability and reliability of the system.

4. Program List