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Indicator Circuits   Page 2
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Last Updated on:
Friday, October 16, 2009 03:43 AM
 

Circuits designed by Dave Johnson, P.E. :
  • DC Current Indicator 6  NEW
    The circuit below is a simple way to indicate when DC current is flowing through a wire.  The circuit is designed so it will turn on a LED indicator light, whenever the voltage drop across a shunt resistor exceeds about 0.1 volts.  The value of the resistor can be selected based on the desired current flow. Although I show a circuit for 12v operation, the circuit can be used over a wide range from 3v to perhaps 24v....
  • Electrical Current Indicator
    I designed this circuit as a simple current indicator for any load ranging from 40 watts to 250 watts.  The circuit turns on a small LED, whenever it detects current flowing to a remote load.

Links to electronic circuits, electronic schematics, designs for engineers, hobbyists, students & inventors:
Cellular Phone calling Detector - Flashes a LED when detecting an incoming call.  Powered by one 1.5V cell  (added 4/05)
Charge Indicator Gauges Lead Acid Batteries - 05/27/99 EDN-Design Ideas:.....(design idea added 11/05)
Circuit Detects Current Pulses - 01/06/94 EDN-Design Ideas: 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.....(design idea added 3/03)
Circuit Forms Low Frequency Circulator - 10/11/01 EDN-Design Ideas: The electronic circulator made its debut ten years ago (Reference 1). It functioned at VHF as a three-port unit using a Comlinear (now part of National Semiconductor, www.nsc.com)CLC 406 operational amplifier. The circuit in Figure 1 extends the circulator's performance to four-port operation at low frequencies, using the readily available 941 (equivalent to the ubiquitous 741)and LM3.....(design idea added 1/05)

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 idea added 1/05)
Circuit indicates ac mains fuse failure - 01/08/09 EDN-Design Ideas: ,  Use this circuit to alert you when a fuse fails.....(design idea added 08/09)
Contactless Mains Voltage Indicator - (circuit / schematic design added 11/06)
Cut Phone Line Detector (Aaron Cake) - Can be used to alarm security system (added 2/03)
Cut Phone Line Detector (Tony van Roon) - (schematic / circuit added 10/02)
CW Zero Beat Indicator - (electronic Circuit / Schematic added 7/03)
CW Zero Indicator - (electronic circuit added 7/03)
Data Multiplexer Adds Cursor to LED Display Driver - 03/30/95 EDN-Design Ideas: (design idea added 03/03/03)
DC Current Indicator #4 - The circuit below uses some common components to turn on an LED whenever DC current above a certain level is detected.  The circuit uses a very popular LM393 dual voltage comparator from National Semiconductor and a common 1N4148 signal diode.  The diode acts as a crude 0.7v voltage reference.  Only one of the comparators inside the 8 pin package is used.  A pair of resistors across the diode forms a voltage divider, which produce a reference voltage of about 0.015v. .... ….(designed by David A. Johnson)
DC Current Indicator 6 - The circuit below is a simple way to indicate when DC current is flowing through a wire.  The circuit is designed so it will turn on a LED indicator light, whenever the voltage drop across a shunt resistor exceeds about 0.1 volts.  The value of the resistor can be selected based on the desired current flow. Although I show a circuit for 12v operation, the circuit can be used over a wide range from 3v to perhaps 24v.... ….(designed by David A. Johnson)
Digital Mains Voltage Indicator - (electronic Circuit / Schematic added 10/04)
Doorbell for the Deaf (Andy Collinson) - This circuit provides a delayed visual indication when a door bell switch is pressed. In addition, a DPDT switch can be moved from within the house which will light a lamp in the door bell switch. The lamp can illuminate the words "Please Wait" for anyone with walking difficulties.....(schematic / circuit design added 9/02)
Doorbell Indicator-Remote - (electronic design added 6/07)
Electrical Current Indicator - I designed this circuit as a simple current indicator for any load ranging from 40 watts to 250 watts.  The circuit turns on a small LED, whenever it detects current flowing to a remote load. ….(designed by David A. Johnson)
Expanded scale indicator revisited - 08/08/02 EDN-Design Ideas: The visualization aid that a previous Design Idea describes allows only the expansion of the upper end of the scale (Reference 1). But what can you do if, according to your project requirements, you need to expa.....(design idea added 1/05)
Fastest Finger First Indicator - (electronic Circuit / Schematic added 10/04)
Flashing LED Power Indicator Draws Low Current - This circuit flashes a power indicator LED to keep the average current low. ….(designed by David A. Johnson)
Free Line Indicator Stops Interruptions - 12/07/00 EDN-Design Ideas: / When only one phone line is available for two phones, each time you want to make a call, someone may be using the second phone. A simple circuit lights an LED, which indicates whether the line is free (Figure 1a). Batteries are unnecessary; the phone line powers the circuit, and an accumulator saves energy for an "in use" indication.....(design idea added 11/05)
Free-line indicator stops interruptions - 12/07/00 EDN-Design Ideas: PDF contains multiple circuits, scroll to find this circuit….When only one phone line is available for two phones, each time you want to make a call, someone may be using the second phone. A simple circuit lights an LED, which indicates whether the line is free (Figure 1a). Batteries are unnecessary; the phone line powers the circuit,.....(design idea added 4/02)
Fuse Monitor/Alarm - a simple way to see if a fuse has blown without removing it from its holder (added 4/02)

 

Indicator Circuits:  #'s - B       C - F       G - O     P - S       T - Z

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