Development of single chip microcomputer for intelligent exhaust fan controller

1、 Overview:

We designed an intelligent exhaust fan controller with HT46R23 single chip microcomputer. The controller can control the exhaust fan speed (automatic mode) according to different temperatures. At the same time, it has infrared remote control function. It can manually control its working state (divided into I, II and III gears), and can also control its on and off. The infrared control distance can reach about 7m. The control also has the function of temperature and humidity indication. The temperature display accuracy can reach ± 1 ℃ and the humidity display accuracy can reach 5%. At the same time, it has the alarm and control function of dangerous gas (which can be sensitive to natural gas, liquefied petroleum gas, gas, carbon monoxide, alkanes, alcohols, gasoline, liquid vapor and smoke). Once the dangerous gas is detected, it will automatically work in the forced gear III state and exhaust to the maximum extent. At the same time, the buzzer will give an alarm..

We use the PA port of HT46R23 as the bit port line to output digital bit data, and other spare ports (depending on the convenient PCB layout, any five I / O ports can be used) as the segment drive output. The display unit adopts dynamic scanning display.

PA port is used as the output port. Dynamic scanning requires that the scanning frequency should not be too low, otherwise the displayed number will flicker. Generally, if the frequency is not lower than 50Hz, the flicker can not be felt, which is relatively easy to realize in the program.

Pb0 (an0) - PB2 (an2) is the analog input of temperature mode signal, humidity analog signal and dangerous gas detection signal. It scans and queries the three analog quantities in different periods, converts the temperature analog signal and humidity analog signal into BCD code after a / D conversion, and displays them on LED in time sharing. The signal output by humidity sensor has large nonlinear error and is sensitive to temperature, At the same time, the humidity sensor needs to be driven by AC. we have designed a special amplification, processing and compensation circuit to process and compensate its signal, so that the analog output is basically linear, and the actual measurement shows that the error can reach 5%. This can meet the requirements for general monitoring.

The right figure is the panel diagram of the controller. We set up 5 groups of working status indication LEDs, including power LED, I-III working status indication and Auto LED indication, so that users can see it at a glance. Temperature and humidity show that we use larger led, because the exhaust fan is generally placed in a higher position, and the digital LED is larger for easy observation.

All sensors are equipped with external sockets, which is convenient to place the sensors on the panel and outside of the fan, so as to prevent the temperature and interference of the controller (motor itself) from affecting the measurement accuracy.

Of course, the output current of this control is only about 1a (220V), and a smaller relay is used. If you need to control a larger fan and the output current is large, you can consider changing the relay of the output board, and other hardware and software should not be changed.

The left figure shows the rear output board of the control. The two boards are connected by connectors. The three sensors are printed with wires respectively, and the controller needs a group of 12V (DC, 500mA) power supply. As the gas sensor needs power preheating, the power consumption is relatively large, and about 150mA current is required under + 5V power supply, we use a lm7805 three terminal voltage regulator to supply power, and add an appropriate radiator to ensure reliable and stable operation for a long time. Practice has proved that the measurement of temperature and humidity is accurate, rapid and effective, and is also very sensitive to gas detection. In case of dangerous gas, it can reliably send out an alarm and automatically turn on the fan for exhaust, which plays a high-sensitivity detection and protection role for personnel safety.

It is worth mentioning that the dangerous gas sensor needs preheating, which generally takes about 10 minutes to stabilize, so our gas detection part is effective only after 10 minutes of power on, but it has no impact on use.