Design of intelligent detection control circuit using AT89C205l

　　An "intelligent detection control circuit" for the water boiler 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 corresponding sound and light alarm signals 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.

　　AT89C205l "single-chip computer" chip IC1 is the core of this circuit, and C3 and R3 form a simple power-on automatic reset circuit. JT, C1, C2 and the related pins of IC1 form 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 electrode 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 both 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 1, and 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 software control makes the P1.0 of the single-chip microcomputer output a high level signal intermittently, and the controllable The audio oscillator will work intermittently, making the speaker emit a beeping alarm sound. The 1-7 pins of IC2 form the level conversion circuit of the electric heating tube working status monitoring signal. The electric heating tube working status sensor adopts the TAl420 type, which is a small precision AC current transformer (HGQ1~HGQ3) that is vertical, through-core, and can be directly welded and installed on the printed circuit board. It has the characteristics of fully enclosed, good mechanical and environmental resistance, strong voltage isolation ability, beautiful appearance, high precision, wide sampling range, and flexible application.

　　The specifications of the components required in the circuit are marked in the figure below.

　　

　　When in use, one 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 is working 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 through the three groups of rectifier bridges Q1-Q3 and connected to the 2nd, 4th, 6th (7th) feet of IC2 respectively. After IC2 converts the high level into a low level, it is output from the 1st, 3rd, and 5th feet respectively and connected to P3.4, P3.5, and P3.70 of the single-chip microcomputer. 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 end 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 corresponding indications can be given through the corresponding light-emitting diodes. The DWI~DW3 voltage stabilizing diodes are mainly used for protection, to prevent the output signal of the current transformer from exceeding the VCC working voltage (+5V) of IC2 and damaging the relevant input terminals of IC2. The water level signal sensor uses a normally open (connected when the water level is normal) type 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 P3,3 of the microcontroller. 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 water shortage alarm is a discontinuous high-level signal output by software-controlled P1.0, which controls the audio oscillator to work intermittently, so that the speaker emits 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 the "inverter" circuit, which is output from pin 5 and connected to P3.2 of the single-chip computer. By cooperating with the software, the water temperature state can be accurately identified and the output control end can be used to control whether the electric heating tube is powered on or not. At the same time, the corresponding LED gives 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.