Phone in use indicator by LED
The circuit described functions as an indicator for a busy line, utilizing two surface-mount technology (SMT) transistors for its operation. The primary purpose is to illuminate LEDs when the voltage across the circuit decreases to 40 V, signaling that the line is currently in use.
In terms of components, the circuit includes two SMT transistors configured in a common-emitter arrangement. This setup allows for effective switching of the LEDs based on the voltage levels detected. When the input voltage exceeds 40 V, the transistors remain in the off state, preventing current flow through the LEDs. Conversely, as the voltage drops to 40 V or below, the transistors turn on, allowing current to flow through the LEDs, thus illuminating them.
The LED indicators provide a clear visual representation of the line status, which can be particularly useful in communication systems or other applications where line availability is critical. The choice of SMT transistors is advantageous for compactness and efficiency, allowing for a smaller circuit footprint while maintaining performance.
Additional considerations may include ensuring that the transistors are rated appropriately for the expected voltage and current levels, as well as incorporating suitable resistors in series with the LEDs to limit current and prevent damage. Proper thermal management may also be necessary to maintain the reliability of the circuit under prolonged use.This circuit is useful to show chen your line is busy. I used for this a pair of smt transistor, the leds on when the voltage drop down to 40 v. 🔗 External reference
Related Circuits
A repeater or other unattended equipment can be activated or deactivated using a standard telephone. The process involves calling the remote station, allowing it to ring three times, hanging up, waiting for 20 seconds, redialing the number, and letting...
This is a JFET AC Coupled Integrator circuit. This circuit is used to achieve very high voltage gain. To achieve very high voltage gain, this circuit uses... The JFET AC Coupled Integrator circuit is designed to provide significant voltage amplification...
This stroboscope circuit utilizes 16 high-brightness white LEDs housed within a torch structure. It also offers a signal output to a frequency counter to indicate revolutions per minute (RPM). The stroboscope circuit is designed to provide visual indication of rotating...
.jpg)
This article contains an assembly language listing that requires MAC/65 or the Atari Assembler Editor, along with access to an EPROM burner. The previous three installments were published in the January, February, and March 1985 issues of Antic. This...
An emitter-coupled differential amplifier circuit is designed to suppress zero drift through circuit symmetry. The effectiveness of zero drift suppression improves with better symmetry; however, in practice, achieving complete symmetry is not feasible. Consequently, the basic differential amplifier circuit...
This circuit diagram represents a logic probe based on a single CMOS integrated circuit (IC). The logic probe indicates three conditions: High, Low, and Pulsing. Additionally, no LEDs will illuminate when the probe input is in a high-impedance state,...