RainboW LED indicates voltage with color -  12/07/04  EDN Design Idea   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 than a casual glance to read. An indicator lamp or LED takes little space but . . .  [by David Prutchi, Impulse Dynamics, Haifa, Israel]

Ramping Lamp Driver -  This circuit drives any 12v lamp, incandescent or LED type, in a ramping fashion. Each press of the button toggles the lamp from a fully off mode to a fully on mode. But, instead of an instantaneous lamp intensity change, the power is slowly ramped up a . . . [Hobby Circuit designed by David Johnson P.E.,  12/21/07]

Remote Audio Level Indicator Circuit -  The normal level-indicator circuits which are available in the market require connections to be made to the output of the player, which may not be easily accessible. The audio level indicator circuit described here removes this restriction as it may be placed close to the player’s speakers and yet the desired effect can be. . .  [Circuit posted by Popescu Marian]

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. . .  [by Andy Collison]

Remote LED Indicator Light -  There are times when you would like to transmit a signal from one LED indicator light to second LED at another location. The circuit below works well for this application. It takes advantage of the fact that the internal infrared LED inside an opto-isolator . . . [Circuit by David A. Johnson P.E.,  12/28/08]

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.,  07/09/06]

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. . .  [Design 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.,  12/09/07]

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.,  12/09/07]

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