Message Waiting Flasher:  This circuit starts flashing a neon light when the phone rings and continues flashing it until the phone is picked up to remind you to check your voice-mail. The flashing neon light drives a voltage doubler (Q2) which keeps it flashing. Q1 ensures that the flashing is stopped when the phone is picked up.  (Circuit / schematic design added 6/06)

Model Aeroplane Navigation Strobe/Battery Level Indicator :  Fair Waring, site contains annoying popups.  If you are interested in model aeroplanes and have the capital, a radio controlled electric park flyer is a must have.  An RC aeroplane under 400 grams floats around like the rubber models of my youth and contact with the ground doesn't seems to involve that sickening crunch that comes with larger models. Finding a deserted park in which to fly one (that propellor can still be dangerous) and waiting for a windless day isn't always that easy but it sure beats driving an hour to a club field.  Park flyers are definitely stress beaters and are also just plain fun. (add 5/05)

Off Hook Phone Line Supplies 150 MW:  09/01/94 EDN-Design Ideas / (Circuit / schematic design added 6/06) For systems that require 150 mW or less, the power supply in Fig 1 draws power from ordinary phone jacks without interrupting the voice signal, thereby eliminating the need for batteries and ac adapters. Built into peripheral equipment such as PCMCIA modem cards, this circuit can spare the battery in a host computer. The circuit is useful in portable systems that connect to subscriber (household) telephone lines, such as modems and telephone test sets....    

Opamp Rectifier Signals Input State:  07/21/94 EDN-Design Ideas / (Electronic Circuit diagram added 03/03) The op-amp rectifier in Fig 1 operates from a single supply and provides a logic output and an LED that indicate the state of the input voltage. The input-state indications are handy for calibration. Because the circuit operates from a single supply, the 2.5V reference determines the level around which the circuit rectifies input waveforms.... 

Park Aid:  3-LEDs signal bumper-barrier distance Infrared operation, indoor use (Circuit added 9/04)

Peak Level Indicator:  Dot-mode three-LED display.  9V battery powered portable unit (circuit design added 3/05)

Phone Busy Indicator:  simple busy indicator, does not meet regulations of many countries because this circuit draws excessive continuous current from the ph1-line even when not active and this can cause problems with Telephone system (Electronic Schematic / circuit added 4/02)

Phone in Indicator:  (circuit added 7/02)

Power Amplifier Clipping Indicator:  (added 9/02)

Rainbow LED Indicates Voltage with Color:  12/07/04 EDN Design Ideas  / (added 1/05)  Meters that indicate analog levels via a moving-pointer meter, a numeric display, or a column of LEDs typically occupy considerable panel area and require more than a casual glance to read. An indicator lamp or LED takes little space but indicates only an on or off condition. However, an unobtrusive LED that changes color as a function of a measured value would enable an observer to easily asse...

Remote Doorbell Indicator:  (added 9/02)

Safety Indicator Lights:  SILs was designed and built for a colleague at work. He needed a device to control the indicator lights on his motorcycle. The idea was to turn all lamps on during driving, but switch over to normal operation when the indicator was needed. He wanted this device because his motorcycle was fairly broad and was worried that passing cars wouldnt notice, especially in the dark! (Electronic Circuit diagram added 03/03) (Electronic Schematic / circuit added 4/02)

Simple Circuit Detects Current Pulses:  01/06/94 EDN-Design Ideas / (Electronic Circuit diagram added 03/03)  The pulse detector provides 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.

Simple Circuit Forms Peak/Clipping Indicator:  11/22/01 EDN Design Ideas  /  (added 1/05)  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. ...

Single LED Indicates Two Power States:  12/05/96 EDN-Design Ideas / (Electronic Circuit diagram added 03/03)   -- Uses a single bicolor LED to indicate both power-on and blown-fuse conditions

Status Indicator Flags Five Discharge States:  01/20/94 EDN-Design Ideas / (Electronic Circuit diagram added 03/03)  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 on at2 Hz is the batterys last gasp. And, when the LED is continuously off, its Time to replace the battery.

Telephone in Use Indicator #2:  (Electronic Circuit / Schematic added 10/04)

Telephone in Use Indicator:  With this circuit mounted in or near every phone in the house, it will allow users to know if the phone is being used and not to pick up the phone. When a phone is taken off hook, the voltage across the tip and ring terminals drops to 10 volts or less. This will cause the FET (2N4360) to turn on and also turn on the transistor (2N2222). When the transistor turns on it will allow current to flow through the LED and make it light. A blinking LED could be used to make the effect better.  (Circuit / schematic design added 6/06)

Telephone in Use LED Indicator:  (Electronic circuit added 7/03)

Telephone In-Use LED Indicator:  (Electronic circuit added 4/05)

Three Level Audio Power Indicator:  Battery-operated Three LED display that connect it to loudspeaker output (Circuit added 9/04)

Transistor protection by transil-power and surge current duration:  AN444  (Circuit / schematic design added 6/06)

Triple-Supply Power-Good Indication with the ADM108x:  AN-726 - Analog Devices Application Note (app note added 6/06)

Ultra Low Power LCD Indicator:  This circuit serves as an ultra-low power replacement for multiple LED on-off indicators. It also has the advantage of being easy to read in full daylight. With the parts shown, it is possible to display four bits of information. The display that I used has three digits and 2 decimal points for a total of 23 segments. Different groupings of segments can be ... (Circuit / schematic design added 6/06)

Water Level Alarm:  (added 9/02)