In the following article you will find a new practice of electronics . Many times we need to measure the temperature of a circuit or somewhere and do not have a thermometer, since only some – usually more sophisticated and expensive- multimeters have it . So that we will not pass share this circuit, together with a voltmeter commonly used in the range of 20 volts DC, it will give us a fairly approximate value of the temperature value . Let’s do it!
Again we shared a practical project electronics , very useful for both amateur and professional. A montage included in one of the magazines Todoelectronica , in which each number can be found several practical projects. We started …
They are needed to build a few components of general use and are very easy to find. It can be constructed in a universal plate islands or on a breadboard. The only special consideration is that the transistor 2N2222 must be as close as possible to the circuit, to avoid possible interference with the measurement value for noise pickup. It is advisable to use a metal encapsulated transistor , but in case you can not get into the electronics store, the plastic will also work.
For mounting on a plate islands, one must be careful not to overheat much or transistor or operational amplifier.
Its operation is very simple. The operational amplifier serves as the voltage comparator at its inputs marked ‘+’ and ‘-‘. The noninverting input voltage has a fixed, adjustable by a variable resistor 10K , which will use it to calibrate the circuit.
A connect to the other input transistor, which varies its ‘internal resistance’ as the temperature varies. In conclusion, the circuit compares two resistors , set by us in the calibration and giving us the transistor. If we connect the output to a voltmeter on the scale of 20 volts DC, the voltage at the output of the operational result in a temperature measured at the voltmeter.
For those who want greater accuracy, it is recommended to replace the transistor by a thermo-braked and use resistors of a 1% tolerance.
For the adjustment should take two measurements and contrast with other temperature meter. With the two variable resistors to halfway, a measurement with a calibrated thermometer at a temperature of about 0 ° and the potentiometer connected to pin number 5 of the operational amplifier is regulated be taken.
Once such regulation will be measured about 90 and the potentiometer connected to voltmeter to measure 90 is regulated.
Regarding circuit power is recommended to do with a voltage regulator of the type 7812 or 7815 to obtain a stabilized voltage. Thus if this value varies also vary measuring and misreads be obtained.
Once regulated the circuit with a voltmeter always certain measures should be done with it. Should change its internal parameters vary instrument, so it would have to return to contrast the instrument.
Electronic learning continues
If you found interesting this assembly, remember that each issue of the magazine Todoelectronica contains proposed by us and by readers circuits. In addition, if you want to keep learning electronics, we recommend performing Course Electronics theoretical and practical Todoelectronica.