Circuit Project: Heat Detector Alarm using UM3561

A very simple heat detector alarm electronic project can be designed using the UM3561 sound
generator circuit and some other common electronic parts . This heat detector electronic circuit
project uses a complementary pair comprising npn and pnp transistor to detect heat Collector of
T1 transistor is connected to the base of the T2 transistor , while the collector of T2 transistor is
connected to RL1 relay T3 and T4 transistors connected in darlington configuration are used to
amplify the audio signal from the UM3561 ic.

When the temperature close to the T1 transistor is hot , the resistance to the emitter –collector
goes low and it starts conducting . In same time T2 transistor conducts , because its base is
connected to the collector of T1 transistor and the RL1 relay energized and switches on the siren
which produce a fire engine alarm sound. This electronic circuit project must be powered from a
6 volts DC power supply , but the UM3561 IC is powered using a 3 volt zener diode , because
the alarm sound require a 3 volts dc power supply. The relay used in this project must be a 6 volt
/ 100 ohms relay and the speaker must have a 8 ohms load and 1 watt power.