Adjustable threshold temperature alarm

As the resistance (Rl) increases with a decrease in temperature, the output of integrated circuit IC1 becomes positive, activating transistor Q1. When Q1 conducts, it also triggers transistor Q2, which in turn activates the audible alarm. The threshold level for this operation is adjusted using potentiometer R2.

The circuit described operates as a temperature-sensitive alarm system. In this configuration, the resistance Rl is inversely related to temperature, meaning that as the temperature drops, Rl increases. This increase in resistance affects the voltage level at the output of IC1, which is likely a comparator or operational amplifier configured to monitor the voltage across Rl.

When the output of IC1 goes positive, it indicates that the measured temperature has dropped below a predetermined threshold. This output is used to turn on transistor Q1, which acts as a switch in this circuit. The conduction of Q1 allows current to flow to transistor Q2, which is connected to the audible alarm. Thus, when Q2 is activated, it completes the circuit for the alarm, resulting in an audible signal indicating a low-temperature condition.

The threshold for triggering this alarm is adjustable through potentiometer R2. By varying the resistance of R2, the reference voltage at the input of IC1 can be altered, allowing for customization of the temperature level at which the alarm will activate. This feature is essential for applications requiring specific temperature monitoring, such as in refrigeration systems or environmental controls.

Overall, this circuit provides a simple yet effective means of monitoring temperature changes and alerting users when conditions fall outside of a desired range. The use of transistors for switching and an adjustable potentiometer for threshold setting enhances the flexibility and functionality of the design.When Rl increases as temp decreases, the output of IC1 goes positive, turning on Ql. Ql conducts and causes Q2 to conduct, turning on the audible alarm. The threshold is set with potentiometer R2. 🔗 External reference