To replace the not very convenient analog temperature meters, which are based on the ability of the liquid to expand and contract, the industry has proposed discrete devices. These very simple devices have a number of undeniable advantages. You can buy a meter in almost any household or climate equipment store, but it is much more interesting to make an electronic thermometer with a remote sensor yourself.
The essence of the device
Thermometer, colloquial analogue - thermometer, designed to measure ambient temperature. The first device was invented in 1714 by the German physicist D.G. Fahrenheit. At the base of his design, he used a transparent sealed flask, inside of which was alcohol. After that, the scientist used mercury as a liquid. But the analogue meter scale, which exists to this day, was developed only 30 years later by the Swedish astronomer and meteorologist Anders Celsius. For the starting points, he suggested taking the temperature of melting ice and boiling water.
An interesting fact is that initially the temperature of ice melting was noted by the number 100, and the boiling point was taken as zero. Subsequently, the scale "turned upside down." In some opinions, Celsius himself did it, in others - his compatriots botanist Linnaeus and astronomer Stremer.
Soon, the manufacture of mercury meters was widely established on an industrial scale. Over time, mercury was replaced by alcohol due to its toxicity., and then a new type of device was proposed - digital. Today, perhaps, the thermometer has become an integral attribute of any home. On the advice of the World Health Organization, the Minamata Convention was adopted, aimed at the gradual decommissioning of mercury thermometers. According to it, in 2022, the use of mercury in meters will be completely discontinued.
Therefore, because of its excellent characteristics, a thermometer with a digital circuit has virtually no competitors. The alcohol devices on sale lose to him in accuracy and convenience of data perception.
Electronic models can be located anywhere, because in a controlled room you need to place only a small sensor connected to the device. This type is used in many technological processes of industry, for example, construction, agricultural, energy. With their help, it is controlled:
- air temperature in industrial and residential buildings,
- checking the heating of bulk products,
- condition of viscous materials.
Principle of operation
Before proceeding directly to the manufacture of an electronic thermometer, you should understand the principle of its operation and determine which units the structure will consist of. Industrial-produced electronic thermometers vary in size and purpose. But they are all built on the same principle of action.
The conductivity of the material varies with ambient temperature. Based on this, the electronic thermometer circuit is designed. So, most often a thermocouple is used in the design. This is an electronic device consisting of two metals welded together. On the surface of each of them there is a contact pad connected to the measuring circuit. When the contacts are heated or cooled, a thermoelectromotive force arises, the appearance and change of which is recorded by the electronics board.
A new generation of devices uses a silicon diode instead of a thermosensitive element. A semiconductor radio element in which the voltage-current characteristic is dependent on the temperature effect. In other words, with direct connection (current direction from the anode to the cathode), the value of the voltage drop across the junction changes depending on the heating of the semiconductor.
The processed data is displayed on the display, which is already visually removed by the user. Digital thermometers allow you to measure temperature changes in the range from -50 ° C to 100 ° C.
In total, five blocks can be distinguished in the design of a simple thermometer:
- A sensor is a device that changes its parameters depending on the magnitude of the temperature acting on it.
- Test leads - used to remove the sensor and its location in various places that require temperature control. Most often, these are small cross-sectional diameters of conductors, even optionally shielded ones.
- Electronics board - contains an analyzer block that records changes in the signal coming from the sensor, and then transfers it to the screen.
- Display - monochrome or color screen, designed to display data on the measured temperature.
- Power supply - is assembled on integrated circuits typical for radio electronics. Used to stabilize and convert the power supplied to all nodes of the board.
What is it for
A similar paper product can be used in lessons and at home. A homemade cardboard thermometer will not break, even if a child drops it. In addition, a similar model of the measuring device will help teach children to determine the temperature and solve various problems. Cardboard thermometers are often used for conducting classes on maintaining a weather calendar. In addition, a paper measuring device can be hung on the wall in a children's room. This will help the child better understand what zero, negative and positive numbers are. As a result, it will be easier for your child to establish a connection between the weather changes outside the window and the readings of the measuring device.
What is needed for this
Creating a thermometer from cardboard with your own hands is not so difficult. This does not require much experience. So, to make a paper measuring device, you will need:
- A simple pencil.
- Bright felt-tip pen or ballpoint pen.
- Sewing needle with a sufficiently large eye.
- Thick threads of white and red.
- Half board or light-colored cardboard.
It is better to prepare all components in advance, so that you can not look for anything later.
Making a blank
After that, make a marking on a strip of cardboard, which will be a scale: from "minus" 35 to "plus" 35 ° C. Without fail, circle all the numbers and lines with a bright felt-tip pen or a ballpoint pen. Take the cardboard and mark with a simple pencil a strip 5 centimeters wide and 12 centimeters long. Gently cut it out.
To make a neater cardboard thermometer with your own hands, you can use a printer. To do this, simply draw a scale with all the marks using special programs. Highlight all the numbers in bright colors to make them more visible. Print the finished scale on the printer. It is worth noting that such a model of the measuring device will look more aesthetically pleasing.
Create a thermometer column
In order for the thermometer to work and show the temperature, it is necessary to create a column of mercury. To do this, take the red and white thread. Tie them together. Then take a sewing needle and thread a red thread into it. Puncture the thermometer scale at the very top. Pull the thread end from the back of the cardboard. After that, thread a white thread into the needle and pierce the scale at the very bottom. On the back of your measuring device, connect the ends of the threads, making a strong knot. As a result, the thread can be moved.
Games with a paper thermometer
You made a paper thermometer with your own hands and now you don’t know what to do next. There are many games that allow you to introduce your child to the device. First, explain to your child how the thermometer works. Move the threads so that the red becomes above zero. After this, invite the child to speculate what happens in nature at this temperature. For example, the sun shines, people put on light clothes, it’s very hot. When the red thread is below the zero mark, then tell the child what is happening with nature. For example, water freezes, everything is covered with ice, snow falls and so on.
How to make a medical thermometer out of cardboard
All children love to play role-playing games. For the "hospital", you can also make a cardboard thermometer with your own hands. To do this, you need: paper, pencil, pen or felt-tip pen, thread and needle.
To get started, take a sheet of cardboard and draw on it the contours of the future thermometer. Carefully cut the workpiece and draw a scale on it. It should be the same as on a real thermometer.
Take two threads. One should be red, and the second white. Connect them. Pass the red thread to the lowest mark of the scale, and the white thread to the top. Connect the ends on the back of the thermometer and cut off all the excess.
The principle of operation of such a model is quite simple. The thread can be moved. Red color indicates body temperature. By moving the thread, you can change the indicator.
How to play with a cardboard medical thermometer
After completing the manufacture of a cardboard thermometer, first of all explain to the child why he needs it and how to use the measuring device correctly. Also tell him what the body temperature of a healthy and sick person is. Teach your child to put the thermometer correctly. Explain to him what the increased and decreased body temperature means. Perhaps in the future your child will want to become a doctor thanks to such a game. Teach your child to use the meter correctly. At the same time, you can tell us why a real thermometer is dangerous.
The best learning option is co-manufacturing a thermometer. In the process, you can tell the child what it is, why it is needed, how to use it correctly, and also in what units the temperature is measured.
As you can see, anyone can make a thermometer from cardboard with their own hands. The whole process takes a little time. The result is an ideal fixture for illustrating and educating children. In addition, the manufacture of a thermometer requires a minimum of cost. So, now you know how to make a thermometer out of cardboard. But this is not enough. You also need to know how to use it correctly. It is worth noting that such paper models of measuring instruments contribute to the mental development of children. Be sure to involve your child in the manufacture of a cardboard thermometer. After all, do-it-yourself crafts, children like more. In addition, this encourages them to be more careful about things.
It is not difficult for a person who is fond of amateur radio to make an electronic thermometer according to the scheme, but at the same time, an ordinary consumer will need to have at least soldering skills. Today, there are quite a few different schemes that differ in both the complexity of repetition and the scarcity of radio components.
When choosing a circuit, take into account the characteristics that it can provide to the future measuring device. First of all, this is the range of measured temperatures, and secondly, the error. Structurally, you can assemble a wired and wireless model. When assembling the second type, a radio module is used, which significantly increases the cost of the product.
Due to the use of sensitive specialized microcircuits, it is unlikely that it will be possible to assemble a surface mounted circuit. Therefore, a printed circuit board is prefabricated. It is better to make it from one-sided foil-coated fiberglass using the "laser-iron technology" method.
The essence of the method is that, using, for example, Sprint Layout, a printed circuit of the device is drawn and printed in mirror image at a 1: 1 scale on a laser printer. Then, applying the printed image face down to the foil layer, iron the drawing with a heated iron. Due to the characteristics of the toner, the image of the lines is transferred to fiberglass. Next, the board is immersed in a bathroom with a reagent, for example, FeCl3.
You can use an LED matrix as an indicator, but it is better to purchase any monochrome screen. A simple screen can be taken literally for “pennies,” for example, it is suitable for old system units made in the AT form factor. If you plan to design with a remote sensor, then a good option would be to use a loop with a conductor diameter of 0.3 mm2, but in principle, any wire will do. In this case, the larger the sensor is, the larger the cross section is needed and the wire.
The circuitry of some thermometers uses microcontrollers. Their application allows to simplify the electrical circuit and increase functionality, but at the same time requires programming skills and the ability to download firmware. To do this, you need a programmer, which can also be soldered independently, for example, for LPT of five wires.
The design of a simple thermometer consists of only three parts and a tester. As a temperature sensor, the circuit uses LM35. This is an integrated device with a calibrated voltage output. The amplitude at the output of the sensor is proportional to the temperature. The measurement accuracy is 0.75 ° C. You can power the integrated circuit both from a unipolar source and a bipolar one. Measurement range from -55 ° to 150 ° C.
As a multimeter, you can use a pointer or digital device. According to the scheme, a power source is connected to the sensor. For example, CROWN or three finger batteries connected in series. The meter is connected to the V and COM terminals and transferred to the temperature measurement mode. The sensor consumption during operation does not exceed 10 μA.
The measuring range of the multimeter is set to two volts. The result displayed on the screen will correspond to the measured temperature. The last digit in the number indicates tenths of a degree.
If desired, the device can be made dual-channel. For this, it will additionally be necessary to manufacture a mechanical or electronic switch.
One of the simplest schemes consists of only a few elements. The design is based on the use of a sensor that outputs a temperature value in a digital code. The cost of the LM 335 temperature sensor does not exceed 50 cents, and after calibration, its measurement accuracy is from 0.3 ° to 1.5 ° C. The sensor can measure temperature from - 40 ° to 100 ° C. It is available in two cases - TO- 92 and SOIC. As an analogue, you can use the domestic chip K1019EM1.
During installation, the length of the connecting wires can reach five meters. The circuit is calibrated by changing the voltage applied to pin one. The required value is calculated by the formula:
Uout = Vout1 * T / To, where:
- Uout - voltage at the output of the microcircuit,
- Uout1 - output voltage at a reference temperature,
- T and To are the measured and reference temperatures.
The voltage that forms the output signal depends on the temperature, so the power supplied to the sensor must be supplied from a current source. It is assembled on two transistors KT209 and does not require additional settings. The maximum supply current does not exceed 5 mA. An increase in the output voltage by 10 mV corresponds to a temperature increase of one degree.
The use of a microcontroller in a homemade thermometer circuit involves the use of a program that controls its operation. The ATmega8 is used as the chip, and the DS18B20 is the temperature sensor.
The circuit uses a small number of radio components. It is simple and does not need any adjustment after assembly. The power supply voltage of the microcontroller is five volts. To stabilize it, the L7805 chip is used. Transistors can be used with any NPN structure. A three-digit segment display with a common cathode is suitable as an indicator.
The temperature of the device can vary in the range from -55 ° to 125 ° C in increments of 0.1 ° C. The measurement error does not exceed 0.5 ° C. Data is exchanged between the sensor and the microcontroller via the 1-Wire bus. With a large offset distance of the measuring chip DS18B20 from the ATmega8, it is necessary to select a pull-up resistance. It is better to unsolder it directly to the output of the sensor.
When programming, all the settings of the microcontroller are left at the factory, and the fuses are not changed. Then, you can add another sensor to the assembled thermometer, as well as a clock. But for this it will be necessary to have knowledge in programming in order to complete the program code.
The use of semiconductor diodes and transistors as sensors is characterized by the complexity of calibrating the readings, which ultimately leads to an error in the measurement result. Therefore, to obtain an accurate result, a bifilarly wound coil of thin conductor placed in a cylinder measuring about 4 × 20 mm is used as a meter.
The basis of the design is the ICL707 chip and a luminous indicator. Power can be supplied from any source with an output amplitude of 12 V. A normalizing converter is assembled on DA3, which changes its output voltage depending on the signal received from the sensor.
The setting consists in setting a voltage of one volt on the 36th leg of the microcircuit. Делается это с помощью резисторов R3 и R4. Вместо датчика подключают резистор на 100 Ом. Изменением сопротивления R14 устанавливают нули на цифровом индикаторе.Then the device is ready for measurements.