Realization of precision temperature controller with general single chip microcomputer

1. Overview:

In some special fields and occasions, we need precise temperature control, such as bioscience experiments, biological tissue research, medical clinical testing, environmental science testing, biological enterprise testing and so on. The experimental equipment in these fields needs the experimental equipment with wide temperature range and precise temperature control. The NC dry heating controller is the most suitable equipment. We use a general single chip microcomputer plus an ad conversion chip to realize this function. It has high cost performance and accurate temperature control. The design requirement is ± 0.3 ℃, and the precision control of ± 0.2 ℃ or even ± 0.1 ℃ can be realized in most cases. Wide controllable temperature range, single-phase power supply is used, and large fluctuation of power supply voltage is allowed. At the same time, customers can calibrate and memorize the calibration value at any temperature point, and the calibration data can be maintained for decades even if the power is off. Biological experimental equipment is also often called dry heater, dry bath or metal bath.

2. Technical indicators:

Temperature range: room temperature + 5-150.0 ℃

Temperature control resolution: 0.1 ℃

Temperature control consistency: ± 0.2 ℃

Temperature control accuracy: ± 0.3 ℃

Service voltage: 220V (50Hz) or 110V (60Hz) ± 15%

Heater power: 100W

Display mode: LED or LCD

3. Control block diagram:

4. Circuit structure:

In order to reduce the cost, we do not use the MCU with built-in AD converter, because the price of the MCU with built-in 12bit AD converter is generally high. We still use a general low-cost single chip microcomputer and a small ad converter to realize it. This product has the highest cost performance. There are many models that can be selected by general single chip microcomputer. As long as its resources are basically sufficient, such as I / O pin, timing interrupt or external interrupt resources, there is no need for redundant resources in this product, so as to reduce the cost as much as possible and improve the competitiveness of the product. Because as long as the accuracy and stability of the AD converter meet the requirements, the single chip microcomputer processes the digital signal, which has no impact on the measurement accuracy.

AD converter can be selected: ad7091,12bit, 1ch 8-Lead lfcsp package.

AD converter can be selected: ad7170,12bit, 1ch lfcsp package.

AD converter can be selected: ad7171,12bit, 1ch lfcsp package.

AD converter optional: ad7153,12bit, differential input, 2.7-3.6v, 1ch, 10-msop package.

AD converter optional: ad7276,12bit, 1ch SOT23-6 package. wait

AD converter can be selected: ads1110,12-16bit, 1ch SOT23-6 package. wait

There are many models that can be selected by single chip microcomputer. Considering the requirements of this circuit, 4-bit 7-segment nixie tube is used to display the temperature value. 12 I / O port lines are required for LED display, 3 I / O port lines for communication with AD transponder, 3 I / O port lines for LED indicator light, 2 buzzer control and output control, 3 keyed input and 2 I2C communication with memory. A total of 25 I / O port cables are required. Of course, the circuit can also be designed to share some I / O ports for partial output and input, or use a single chip microcomputer with a low-resolution AD converter (the price is also very cheap) to use an ad port line to complete the function of multiple input keys. It can be used as multiple I / O ports by writing the corresponding piezoelectric identification code in the program.

This kind of single chip has optional models for almost any series of single chip microcomputer, such as ATMEL's AT89C51 with C51 core, Winbond's w79e2051, ht48 series and ht46 series of Taiwan hotekg company. Elan's em78p447, of course, microchip's corresponding MCU also has many optional models. The corresponding single-chip microcomputer model can be selected according to the preference of design engineering, the choice of cost performance and the difficulty of procurement.

When using, as long as we need to set the desired temperature value, it can be accurate to 0.1 ℃. Press the "start" key, and the heating body (aluminum metal module) can reach the set temperature value in about 20-30 minutes. The 4-bit 7-segment nixie tube displays the current temperature value. At this time, the experimental carrier can be put into a constant temperature heater for experiment and test.