·         RS232 Data Bus Status Indicator
This circuit indicates TXD and RXD activity.  The thresholds are set at plus 3 volts and minus 3 volts.

• RS232 Serial Interface Status Indicator
  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.

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

Peak Level Indicator:  Dot-mode three-LED display.  9V battery powered portable unit (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 (added 4/02)

Phone in Indicator:  (circuit added 7/02)

Phone in Use Light:  (electronic circuit added 7/03)

Phone in Use:  (electronic circuit added 7/03)

Phone Off Hook Indicator:  (electronic circuit added 7/03)

Phone Rang' Indicator Light:  (electronic circuit added 7/03)

Power Amplifier Clipping Indicator:  (schematic / circuit design added 9/02)

Quiz Show Indicator:  ASCII format (added 4/05)

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:  (electronic design added 9/02)

Remote Doorbell Warning Switch:  This circuit should only be used with the solenoid type chime doorbells, the electronic type that play tunes will not work here. The hardest part for this circuit was the title. It is quite easy to miss the sound of a doorbell if you are watching TV , this circuit gets round the problem by providing a visual indication, i.e. a lamp. As an alternative, a LED could also be used. You could just parallel a lamp across the doorbell, but this would mean extra drain from the doorbell batteries or transformer. (added 2/06)

Simple Circuit Detects Current Pulses:  01/06/94 EDN-Design Ideas / (added 3/03)  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 / (added 3/03)   -Uses a single bicolor LED to indicate both power-on and blown-fuse conditions

Stabilised Power Supply with Short-Circuit Indication:  (electronic Circuit / Schematic added 10/04)

Status Indicator Flags Five Discharge States:  01/20/94 EDN-Design Ideas / (added 3/03)  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.