Programmable timer temperature controller

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Programmable timer temperature controller [Copy link]

1. Overview:
The programmable timing temperature controller is developed by Shenzhen Zhongyuan Single Chip Computer Development Co., Ltd. The controller has two sets of programmable timers, one set can set the scheduled time for power on, that is, the preparation time, and the other set is the working time. A constant temperature value that can be set arbitrarily. When the scheduled time is up, the output starts to be turned on. The output end can be connected to loads such as heating devices and coolers, and outputs a set of 220V power supply, thyristor or relay as a control element. After the output is turned on, the working time begins to enter the countdown state. During this process, the single chip microcomputer continuously detects the heating or cooling temperature. When the temperature exceeds the constant temperature range, the single chip microcomputer will make corresponding controls and turn on or off the output. Ensure that the controlled temperature is constant within a certain set range. The main functional characteristics are briefly described as follows:

The right figure is a simplified diagram of the control function. The HT46R47 is a high-performance single-chip microcomputer with 4 9-bit (8-bit resolution) channels. It has a very high cost-effectiveness, 13 I/O ports, 8-bit timer/counter, 2k ROM capacity, 64 RAM bytes, and PWM output channels. Such an excellent single-chip microcomputer can be fully applied to general consumer appliances and medical and health care equipment that need to detect analog voltage. The whole machine is managed by an 8-bit microprocessor HT46R47. Two sets of time and temperature values are displayed on the LCD. The LCD driver uses the low-priced HT1621. The HT46R47 and HT1621 are combined to realize the sampling of analog signals and LCD display. This combination makes the price of the whole machine low. The HT46R47 is connected to the HT1621 by three lines, namely chip select (CS), WR (write) and DATA (data line). The display data output by the HT46R47 is decoded and driven by the HT1621.

The whole machine is equipped with 5 buttons, namely the power switch, the start button, the upward setting number key, the down button and the setting key. The setting key can be used to cycle through the appointment time, working time and temperature value. The appointment time and working time can be set arbitrarily from 1 to 9 hours and 59 minutes, and the setting step is 1 minute. The temperature value can be selected arbitrarily from -20 to 99℃. An LED is also set for the backlight illumination of the LCD. When the system is turned off, it will constitute the LED power supply, the LED will go out, the backlight LED will also go out at the same time, and the microcontroller will be in sleep mode. Pressing any key can wake up the system. After setting the appointment time and working time, press the start button to start working, the appointment time starts to count down, and the colon ( between the digital characters of the appointment time will flash at a frequency of 1 second. When the appointment time ends, the buzzer will sound, and the system will enter the working state. The working time starts to count down, and the colon ( between the digital characters of the working time will flash at a frequency of 1 second. The output end outputs a high level, making Q1 conductive, the thyristor conductive, the load is connected to the 220V power supply, and the heating or cooling device works. At this time, the system starts the temperature detection function and closely monitors whether the actual temperature is within the set range. If it exceeds the set range, the output is automatically connected or disconnected to keep the detected temperature within the set range to achieve the purpose of constant temperature. When the entire working time is over, the buzzer will alarm 10 times in succession to prompt the operator to pay attention. At the same time, the output will be cut off, and the system will restore the original set data. At this time, pressing "START" again can also continue the next work. Since the HT46R47 has a total of 4 9-bit A/D channels, we can use one channel to set up a set of power supply voltage detection circuits, so that the entire machine can add an overvoltage protection function by adding only a few resistors and capacitors, so that the load will not continue to be used under overvoltage conditions, effectively protecting the heating or cooling devices.

Since the working current of the whole machine is small, only about 20mA, in order to reduce the product cost, the method of RC voltage reduction can be used to obtain the working power supply of the system, without the need for expensive and large transformer voltage reduction to obtain power. After RC voltage reduction, the three-terminal voltage regulator LM78L05 stabilizes the voltage and provides power to the system. Here we did not use a simpler voltage regulator diode to stabilize the voltage because the reference power supply of the A/D converter in the single-chip microcomputer is taken from the system voltage, which requires a high stability of the power supply to avoid errors in A/D sampling. The temperature sensor uses a low-cost negative temperature coefficient NTC component, which is small in size and has good linearity. In practical applications, selecting a component with good linearity can easily obtain an accuracy of ±0.5℃. This can meet the requirements for general simple controllers.