RFID Smart Key Detector - The hobby circuit below was designed to indicate if a key held over the small coil of wire contains a 125KHz RFID chip. These chips are often used in smart car ignition keys. The left side circuit forms a 125KHz power oscillator, which drives the 680uH a . . . Hobby Circuit designed by Dave Johnson P.E.-July, 2006 Ringing Phone Light Flasher - This is very useful in a situation were there is lots of noise and it is impossable to hear the phone, such as a workshop. Here is such a device. The ring detect part of this circuit came from [url]http://www. hut. fi/Misc/Electronics/circuits/telephone_ringer. html[/url]. Notes: 1. You may need to use a lower voltage zener for D1 and D2.2. You can use a regular relay instead of a solid state relay, but the arcing accross the contacts may destroy it pretty quickly.3. Be very sure that you have not accidentally connected 120V to the phone line when building and installing this __ Designed by Aaron Cake
RS232 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 David A. Johnson P.E.-December, 2007
RS-232 Serial Interface Status Indicator Circuit - 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 volts. Two dual color LEDs are used as indicator lights . . . Hobby Circuit designed by David Johnson P.E.-December, 2007
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.-December, 2007
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.-December, 2007
Simple Stereo Level Indicator - Usually, low-priced home stereo power amplifiers don’t have output level indicators. An output power level indicator can be added to each channel of these stereo power amplifiers. As low levels of...__ Electronics Projects for You
Simple Water Temperature Indicator - When bathing a baby, it’s important that the water is neither too cold nor too hot. You test the water by dipping your fingers in the bath tub before putting the...__ Electronics Projects for You
Simple Circuit Battery-Status Indicator Uses Two LEDs - 08/12/10 EDN-Design Ideas Use LED brightness to indicate battery charge. Design by Abhijeet Deshpande, People’s Education Society Institute of Technology, Bangalore, India
Simple Circuit Blown-Fuse Indicator Sounds an Alarm - 10-Jul-08 EDN-Design Ideas A simple blown-fuse-indicator circuit sounds a buzzer and flashes an LED when a fuse blows Design by Vladimir Oleynik, Moscow, Russia
Simple Circuit Detects Current Pulse - 01/06/94 EDN-Design Ideas The pulse detector provIdeas a visible indication of positive and negative current pulses. The pulses amplitudes can vary from20 to150 mA. The pulses durations can range from10 to40 msec, and their repetition rate can span40 to180 pulses/minute Design by Richard McGillivray, Grey Bruce Regional Health Centre, Owen Sound, Ontario, Canada
Simple Circuit forms peak/clipping indicator - 11/22/01 EDN-Design Ideas 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 capacitor. All the adjustments in the circuit simultaneously apply to both left and right stereo inputs Design by Steven Hageman, Agilent Technologies, Santa Rosa, CA
Simple Circuit indicates a low battery - 02/03/14EDN-Design Ideas 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 Design by James Wood
Simple Circuit Indicates Health of Lithium-Ion Batteries - 05/14/09 EDN-Design Ideas A simple inexpensive circuit quickly indicates a battery pack's health Design by Fritz Weld, Friedberg, Germany
Simple Circuit Moisture indicator - No circuit description, schematic only__ CdS Electronic
Single LED Indicates Two Power States - 12/05/96 EDN-Design Ideas Uses a single bicolor LED to indicate both power-on and blown-fuse conditions. Design by Jim Hagerman, Hagerman Technology, San Diego, CA
Solar Battery Charging Indicator - T.K. HAREENDRANHere is the circuit of a simple charging monitor that indicates whether the storage battery of a solar power unit is being charged or not. It, however, does not tell...__ Electronics Projects for You
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 sound levels but it increases its range 20dB for loud sounds. __ Designed by Audioguru
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 __ Designed by Audioguru
Sound to Light - This circuit gives out a short pulse each time the 220v supply passes through zero. __ Designed by © David Hoult
Stabilised Power Supply with Short-Circuit Indication - Here is an efficient 4-stage stabilised power supply unit for testing electronic circuits. It provides well regulated and stabilised output, which is essential for most electronic circuits to give proper results....__ Electronics Projects for You
Status Indicator Flags Five Discharge States - 01/20/94 EDN-Design Ideas 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%,5-Hz flashing is a warning to have a spare battery on hand. A brief flicker Design by Glen Chenier, Fitel Photomatrix, Nepean, ON, Canada |