Spannungs-/Frequenz-Umsetzer (BC557B, BC547B)

Using a National LM39 l l IC, a l mA meter and a few resistors it is a simple matter to construct a thermometer to measure over the temperature range -20° to +S0°C, which should be adequate for all but polar climates! As the circuit is intended as a room thermometer the entire circuit operates at the temperature which is being measured, so the resistors used should be low-temperature coefficient types to maintain the accuracy of the circuit.