Clock & Timer Circuit DiagramsOscillators Circuit Diagrams

Gated Alarm Schematic Circuit Diagram

Creating a Simple Gated Pulsed Alarm

In situations demanding a straightforward gated pulsed alarm, this circuit stands out for its minimalism. Comprising only four components and a piezo sounder, it is exceptionally simple and unlikely to be surpassed in terms of simplicity. Although it may not deliver the most powerful output, it proves sufficient for a multitude of applications. The core of this design utilizes a dual CMOS timer IC, specifically the 7556, with each of its two sections configured as a basic astable oscillator. It is crucial to note that a standard 556 IC or two standard 555 ICs won’t function in this setup. Additionally, the CMOS7556 is available from various manufacturers, each having their unique type code prefix and suffix.

Utilizing the Dual CMOS Timer IC

This circuit employs a dual CMOS timer IC, the 7556, to achieve the desired functionality. Each half of the IC serves as a straightforward astable oscillator, forming the foundation of this design. Despite its modest output power, this setup is likely to meet the requirements of numerous applications. It’s worth noting that a standard 556 IC or two standard 555 ICs won’t perform as intended in this configuration. Moreover, the CMOS7556 is offered by multiple manufacturers, each labeling it with their distinct type code prefix and suffix.

Selecting the Appropriate CMOS Timer IC

For this design, a dual CMOS timer IC, the 7556, proves instrumental. Each of its sections operates as a basic astable oscillator, contributing to the circuit’s simplicity. While it may not deliver the most robust output, it suffices for many practical applications. It’s important to emphasize that standard 556 ICs or two standard 555 ICs won’t suffice for this specific circuit. Additionally, the CMOS7556 variant is available from various manufacturers, each using their specific type code prefix and suffix. Choosing the right IC variant is crucial for optimal performance.

Gated Alarm Schematic Circuit Diagram

Identifying the Appropriate Texas Instruments Product

The Texas Instruments product corresponding to this configuration will bear the designation ‘TLC556CN’. This specific circuit setup is relatively uncommon, mainly due to the oscillator’s limited load capacity without affecting its timing. Despite this, it proves highly valuable for high impedance logic inputs. This configuration offers a straightforward method to generate a square wave with a 1:1 mark-space ratio, a feat not easily achieved by the conventional setup. IC1.A serves as a slow oscillator, activated when reset pin 4 is set to High and deactivated when it’s Low. The output from pin 5 of IC1.A triggers audio oscillator IC1.B. IC1.B operates similarly: enabled when reset pin 10 is set to High and inhibited when it’s Low.

Utilizing Piezo Sounder as Timing Capacitor and Sounder

To simplify oscillator IC1.B, the piezo sounder (X1) performs the dual function of both timing capacitor and sound emitter. This arrangement is feasible because a passive piezo sounder typically exhibits a capacitance in the range of a few tens of nanofarads, although this value can vary significantly. As the capacitor-sounder charges and discharges, it emits a tone. To optimize the output, the value of resistor R2 must be chosen carefully to match the resonant frequency of the piezo sounder and achieve its maximum volume. The circuit operates effectively within a supply voltage range of 2 V to 18 V. While satisfactory output is attainable at higher supply voltages, it is crucial not to exceed 18 V to maintain the circuit’s stability and reliability.


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