Home weather station. Scheme, description

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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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Home weather station. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Power regulators, thermometers, heat stabilizers

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To observe the weather, several instruments are usually used, each of which measures one parameter. Recently, foreign-made portable electronic weather stations have appeared on sale, but they are quite expensive. The author of the proposed article tried to develop an amateur design of such a device.

The weather station can measure three parameters: wind speed, temperature and atmospheric pressure. Information alternately (after 6 s) is displayed on a four-digit seven-element LED indicator. Four more digits constantly display the current time: hours and minutes with a flashing decimal point.

The scheme of the weather station is shown in fig. one.

(click to enlarge)

The device is based on a microcontroller (single-chip microcomputer) KM1816BE51 or KM1816BE751 (DD1). A three-channel multiplexer on DD5, DD6 chips provides serial connection of one of the three sensors. Next, the signal is fed to the amplifier DA2, and then to the input of the voltage-frequency converter DA3.

The configuration of the weather station may be different. For example, two channels can measure temperature (in the street and in the house), and the third - pressure

Information on the eight-digit display comes from the controller via a serial link. This allows you to move the display (together with the registers and decoders DD2-DD4) to a considerable distance.

All control (setting hours, minutes, turning channels on and off) is carried out by three buttons SB1-SB3. The SB1 button selects the hours, minutes, measurement channel, sets the hours or minutes downward or turns off the channel if the decimal points of the selected parameter are flashing. The SB3 button corrects the clock upwards and turns on the channel if the decimal points of the selected parameter are flashing. The SB2 button performs the "set/select" function. It works in trigger mode. If, after selecting a parameter (one of the buttons SB1, SB3), press SB2, the decimal points of the selected parameter start flashing, now it is possible to set the parameter using the SB1 and SB3 buttons.

The signals from the controller sequentially, after 6 s, connect the next sensor to the input of the amplifier DA2. Synchronously with the selection of the sensor at the input DA3, the positive bias changes. This microcircuit generates a signal at the output, the frequency of which depends linearly on the input voltage.

It is necessary to set the initial offset for all sensors, including sensors operating from zero (wind speed sensor), since the constant 3000 (decimal) is subtracted from the obtained result to determine the temperature sign, and the program for processing the measurement result is the same for all three channels. This makes the device more flexible: there is no rigid binding of sensors to certain channels, it is possible to connect temperature sensors on two or three channels, you can use any of the channels for self-made experimental sensors (a humidity sensor, for example).

From the output of the DA3 microcircuit, the pulse signal is fed to the input of the first timer / counter of the microcontroller. In this case, the second timer is programmed as a clock divider and generates a 625 Hz signal for dynamic indication (display scanning) and a time interval of 1 s, during which the first timer counts pulses from DA3. Further, the constant 3000 (decimal) is subtracted from the received two-byte number in the first timer, the absolute value of the result is divided by 4, rounded off, decimal correction is performed and insignificant zeros are cancelled.

Information is output via the serial port in synchronous transfer mode (shift register). Channel information, changing every 6 s, is displayed on the right four-digit indicator (HG3, HG4), and hours and minutes - on the left (HG1, HG2).

Capacitor C9 is frequency-setting, hence the special requirements for its accuracy and TKE. You can apply K31-10. The capacitance of the capacitor C9 is 4020 ± 40 pF. Capacitor C8 - with a tolerance of 5%. The expensive KM1816BE751 chip (ceramic UFPZU package) can be replaced with an AT89S52 with flash program memory. The table shows the firmware of the DD1 controller.

(click to enlarge)

The temperature sensor RK1 is a copper resistor ESM-03-GR23. It is easy to make it yourself: from a copper wire with a diameter of 0,15 mm, wind a coil with a diameter of 50 mm and, giving it an elongated shape, place it in a ballpoint pen case, after pouring the VGO-1 sealant into it. If the device is supposed to use only one temperature sensor, there is no need to fine-tune its resistance kg: R = 50 ± 5 Ohm. You can also use the integrated temperature sensor K1019EM1, but since at a rated current of 1 mA and zero temperature, the voltage on the sensor, equal to 2,73 V, will saturate the amplifier DA2, the initial bias must be applied to the inverting input DA2. In this case, you need to install a resistor R' and unsolder R18.

Absolute atmospheric pressure sensors are produced by domestic companies: MIDA-DA-53 (MIDA, Ulyanovsk), TDM2-A, PAD-K01 (CJSC "ICNT", Zelenograd). Sensors from foreign companies Bosch and Motorola are more expensive than domestic ones. For example, Motorola's MPX 2200AP sensor costs $15 and is inferior to our sensors in terms of the main parameters: sensitivity and temperature dependence. Such a sensor can be bought on radio markets.

A possible design of the wind speed sensor is shown in fig. 2.

Home weather station

Here: 1 - a cone made of galvanized iron (diameter at the base - 80 mm, height - 75 mm); 2 - a protective screen made of galvanized iron (soldered to the axis); 3 - caprolon bearings; 4 - axis with a diameter of 8 mm from stainless steel; 5 - tachogenerator G1 (electric motor DPN-ZON-19); 6 - rubber hose coupling (it is better to use vacuum rubber); 7 - bracket; 8 - cylinder; 9 - steel spokes with a diameter of 4 and a length of 320 mm.

Setting up a weather station consists in calibrating it using industrial thermometers and barometers. It is more difficult (due to the lack of a reference instrument) to calibrate the wind speed measurement channel. When indicated in Fig. 2 dimensions and using the electric motor DPM-ZON-19 as a tachogenerator, the following dependence was experimentally obtained: U-740 n, where U is the voltage generated by the tachogenerator in millivolts; n is the wind speed in meters per second.

Trimmer resistors R24-R26 adjust the offset, and R12-R14 - the slope of the conversion.

The anemometer will be much more accurate and make it easier if, instead of a tachogenerator, an LED-photodiode optocoupler is used with a shutter rotating between them. The signal from the photodiode can be applied directly to the input of the microcontroller.

Firmware table

Author: S. Semiletnikov, Moscow

See other articles Section Power regulators, thermometers, heat stabilizers.

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