LCD thermometer

This 3 and half digit SP521PR based digital thermometer, it is possible to measure from -40 to +150 degree celsius. It uses S8100 or 1S1588 as thermal sensor. The power consumption is very small and it is possible to operate about 3 months continuously from a 9-V cell.

The forward voltage of the silicon diode changes in the coefficient of -2mV/°C when the temperature with joint changes.

Generally, the 20°C forward voltage is about 600 mV. The forward voltage becomes about 400 mV(600^mV-(2^mV/°C x 100^°C)) when the temperature with joint rises by 100°C and becomes 120°C. At the thermometer this time, it is displaying the change of this voltage as the temperature. The temperature range which it is possible to measure is within the allowable temperature of the diode. It depends on the kind of the diode but it is possible from about -20°C to 150°C. Generally, a diode is enclosed with the package of glass or plastic. So, even if the ambient temperature changes, the voltage of the diode doesn't sometimes change immediately.