ROOM THERMOMETER

ROOM THERMOMETER

ELECTRONIC thermometers have all but replaced the old mercury or alcohol-in-glass types in most applications.The electronic types can usually respond much faster to temperature changes, and also allow the display to beremote from the sensor, allowing greater flexibility in use. They can also be more accurate and, depending on the sensor, can be used over greater temperature ranges. It has to be said, though, that the thermometer design described here is not the last word either in range or accuracy (perhaps a temperature indicator would be a more apt description), as it is intended to display the temperature of a room where neither of these attributes is particularly important. Here the range is limited to 10°C and this is displayed in one degree steps on ten l.e.d.s. These are normally turned off to save power, but may be turned on by means of a pushswitch when a reading is required. Basic Operation All electronic thermometers contain a sensor which converts a change in temperature to a change in some electrical property such as resistance, output current etc. In most cases, this is converted to a voltage which is then further processed (amplified, etc.) before being fed to some sort of analogue-to-digital converter (ADC) and output to a digital display. Of the many different sensors available, a thermistor is used here for simplicity.