Heating Timer

051 GENERAL INTEREST D4 11441 48 I S1 15 09 013 1C3 4060 PI 0 5V 0 Bz O R8 680n BC547B 11•111•11 894071 - 11 DL TOnTOOR 16V 03 Re1 1N4148 D2 T2 3130 1.l6e R4 2 7 55 HEATING TIMER 14 •• 30mA 5V This timer has temperature and time settings. The temperature range is about 150 °C and the time delay is around 25 minutes. The temperature controller, IC2, is driven by sensor IC1, the familiar Type LM35, which produces an output voltage of 10 mV / °C. This voltage is compared with a reference potential provided by a high-stability, temperature-compensated zener diode, Dl. Presets P1 and P2 form the fine and coarse controls respectively for setting the tmperature. The comparator switches on T2 whenever the temperature measured by IC1 is below the set value. This causes the relay, Rel, to be energized so that the heater element is powered via the relay contacts. The timer function is based on oscillator/divider IC3, whose clock frequency is determined by the variable RC network be...