Self Powered AC Indicator -  Often there is a need to monitor when AC current flows into a load. The circuit below works well for this application. It uses an off-the-shelf torrid type AC-1020 current transformer from Triad, available from Mouser. A wire carrying the AC current is . . . [Hobby Circuit designed by Dave Johnson P.E.,  12/30/07]

Self-Powered AC Current Indicator -  Often there is a need to monitor when AC current flows into a load. The circuit below works well for this application. It uses an off-the-shelf torrid type AC-1020 current transformer from Triad, available from Mouser. A wire carrying the AC current is . . . [Circuit by Dave Johnson P.E.,  12/30/07]

Serial Data Bus Status Monitor -  I designed this circuit many years ago and have used it several times since. It uses a single logic IC to indicate the TXD and RXD line activity of a typical RS-232 serial data communications link. The thresholds are set at plus 3 volts and minus 3 volt . . . [Circuit by Dave Johnson P.E.,  12/09/07]

Simple Battery-Status Indicator Uses Two LEDs -  08/12/10  EDN Design Idea   Use LED brightness to indicate battery charge. Properly maintained rechargeable batteries can provide good service and long life. Maintenance involves regular monitoring of battery voltage. The circuit in Figure 1 works in most rechargeable batteries. It comprises a reference LED, LEDREF, which operates at a constant current of 1 mA and provides reference light of constant intensity regardless of battery voltage. It accomplishes this task by connecting resistor R1 in series with the diode. Therefore, even if the battery voltage changes from a charged state to a discharged state, the change in current is only 10%. . .  [by Abhijeet Deshpande, People’s Education Society Institute of Technology, Bangalore, India]

Simple Blown-Fuse Indicator Sounds An Alarm -  10-Jul-08 EDN Design Idea   A simple blown-fuse-indicator circuit sounds a buzzer and flashes an LED when a fuse blows. . .  [by Vladimir Oleynik, Moscow, Russia]

Simple Circuit Detects Current Pulse -  01/06/94  EDN Design Idea   The pulse detector provides a visible indication of positive and negative current pulses. The pulses Amplitudes can vary from 20 to 150 mA. The pulses durations can range from 10 to 40 msec, and their repetition rate can span 40 to 180. . .  [by Richard McGillivray, Grey Bruce Regional Health Centre, Owen Sound, Ontario, Canada]

Simple circuit forms peak/clipping indicator -  11/22/01  EDN Design Idea   The simple peak detector in Figure 1 is the result of a need for a single-5V-supply, level/clipping indicator for a multimedia-PC sound system. The design is unique in that it detects both stereo channels on a single peak-hold. . .  [by Steven Hageman, Agilent Technologies, Santa Rosa, CA]

Simple circuit indicates a Low battery -  02/03/14 - EDN Design Idea   It may seem a bit counterintuitive to power on an LED when a battery is already low, but this Design Idea does it with aplomb. . .  [by James Wood]

Simple Circuit Indicates Health of Lithium-Ion Batteries -  05/14/09  EDN Design Idea   A simple inexpensive circuit quickly indicates a battery pack's health. . .  [by Fritz Weld, Friedberg, Germany]

Simple moisture indicator -  No circuit description, schematic only. . .  [CdS Electronic's website]

Simple Stereo Level Indicator -  Usually, low-priced home stereo power amplifiers do not have output level indicators. An output power level indicator can be added to each channel of these stereo power Amplifiers. As low levels of the output power are not disturbing and damaging to the people, there is no need to add a preamplifier and low-level detector before IC LM3915. But you should know when the output power becomes considerably high. . . .  [© EFY Enterprises Pvt. Ltd. All rights reserved.]

Simple Water Temperature Indicator -  This circuit can also be used to ensure optimal temperature for a room, greenhouse, pool, geyser, fish-tank or freezer. . . .  [© EFY Enterprises Pvt. Ltd. All rights reserved.]

Single LED Indicates Two Power States -  12/05/96 EDN Design Idea    Uses a single bicolor LED to indicate both power-on and blown-fuse conditions. . .  [by Jim Hagerman, Hagerman Technology, San Diego, CA]

Solar Battery Charging Indicator -  Here is the circuit of a simple charging monitor that indicates whether the storage battery of a solar power unit is being charged or not. . . .  [© EFY Enterprises Pvt. Ltd. All rights reserved.]

Sound Level Indicator -  This project uses an LM3915 bar-graph IC driving two sets of ten LEDs for a 30dB range. The circuit is unique because it has an additional range of 20dB provided by an automatic gain control to allow it to be very sensitive to low. . .  [Circuit from Audioguru]

Sound to Light -  This circuit gives out a short pulse each time the 220v supply passes through zero. . . .  [© David Hoult 2013]

Stabilised Power Supply with Short-Circuit Indication -  . . . 

Status Indicator Flags Five Discharge States -  01/20/94  EDN Design Idea   The circuit actually indicates five conditions of the battery. A steady glow assures the user that the battery is strong and healthy. A2-Hz brief flicker off indicates that the battery is starting to show age. A more insistent, 50. . .  [by Glen Chenier, Fitel Photomatrix, Nepean, ON, Canada]

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