Thermometer

from an idea by P Needham At the heart of this simple cir- cuit is the well-known Type KTY10 temperature sensor from Siemens. This silicon sensor is essentially a temperature-de- pendent resistor, which is con- nected as one arm in a bridge circuit here. Preset Pi functions to balance the bridge at 0°C. At that temperature, moving coil meter Mi should not deflect, i.e., the needle is in the centre position. Temperature vari- ations cause the bridge to be unbalanced, and hence pro- duce a proportional indication on the meter. Calibration at, say, 20°C is carried out with the aid of P2. D2 The bridge is fed from a stabil- ized 5.1 V supply, based on a temperature-compensated zenerdiode. It is also possible to feed the thermometer from a 9 V battery, provided Di-D3, 111 and Ci are replaced with a Type 78L05 voltage regulator, because this is more economic as regards current consump- tion. TW 9V RI F0711 fix 1N4001 • pi DI 5V1 720p I6V 86503-1 Cl 1=1