Indicator Electronic Circuits, page 1

Indicator Circuits Page 1
#'s - B C - F G - O P - S T - Z
Last Updated on: Friday, October 16, 2009 03:42 AM

Circuits designed by Dave Johnson, P.E. :
1 LINE TELEPHONE LINE STATUS INDICATOR This circuit is similar to the above circuit, but only monitors one phone line.
1.5V LED FLASHER VERSION A Many published circuits that flash LEDs need 3 volts or more. This circuit uses only a single inexpensive C-MOS IC and flashes the LED for a full year on a single 1.5-volt AA alkaline battery cell. The circuit uses a charge pump technique to provide the LED the needed voltage.
1.5V LED FLASHER VERSION B To squeeze even more energy from a alkaline battery cell, this circuit adds two transistors to a circuit similar to the above design to boost the efficiency. A small 1.5-volt alkaline N cell should flash the LED for a full year. It too uses a "charge pump" technique to provide a LED the needed voltage.
2 LINE TELEPHONE LINE STATUS INDICATOR Many home businesses use multiple phone lines. This circuit gives you a visual indication when a line is in operation. The two AA battery cells should provide enough power for about one year of operation. The circuit is line polarity insensitive.
3v Low Battery Voltage Flasher Many battery powered devices use two AA alkaline cells. Often you will not know when it is time to replace the batteries until the device powered by them actually stops operating. The hobby circuit below can be connected to a 3v battery, to give you some warning when the battery is nearing its end of life. It will flash a LED when the battery voltage drops to about 2.4 volts. The electronic circuit draws only 1ua of current in standby mode and jumps to only 20ua when flashing, so it can safely...
4 LINE TELEPHONE LINE STATUS INDICATOR Many home businesses use multiple phone lines. This circuit gives you a visual indication when a line is in operation. The two AA battery cells should provide enough power for about one year of operation.
12v Lamp Current Indicator This circuit turns on a LED indictor light whenever DC current flows into a 12v lamp. (added 7/06)
AC Current Indicator Light This circuit could be wired into a 120vac power line, which feeds power to any load, ranging from 40 watts to 250 watts. It will turn on a LED light whenever current is being drawn by a load. It is especially useful for remote lights, where you may not be able to see if the lamps are receiving power.
ACCEPTABLE VOLTAGE INDICTOR I have used this circuit many times in custom test fixtures where a simple go-no go indication was needed. The circuit can also be used to adjust a particular voltage be within specific high or low limits. The three LEDs will indicate if the voltage is high, low or OK. When connected to other converters, such as a frequency to voltage converter, a current to voltage converter or a power to voltage meter, it could provide a quick indication of a proper level.
Automotive Electrical Voltage Indicator This circuit will indicate if an automotive electrical circuit has zero volts or 12 volts present. (added 7/06)
Battery Charge Current Indicator This circuit turns on a LED whenever it detects at least 25ma of battery charge current. (added 7/06)
Bad Light Bulb Indicator This request came from a Discover Circuits visitor. He wanted to turn on a LED indicator light whenever a circuit detected a burned out tail/brake light on a car or truck. The circuit shown below uses a transistor switch, to detect current flowing through a low value resistor. If current is flowing to a light bulb, the circuit shunts current around a LED light, keeping the LED turned off. If there is no current detected, the LED turns on. The circuit should operate from 6v to 24v....

Links to electronic circuits, electronic schematics, designs for engineers, hobbyists, students & inventors:

1 Line Telephone Line Status Indicator - This circuit is similar to the above circuit, but only monitors one phone line. ….(designed by David A. Johnson)

1.2-12V/ 1A Low Voltage LED Indicator Power Supply with LM317 - This is a 1.2, 12 V, max 1A power supply with a low voltage indicator LED. The indicator part includes three diodes and one LED. For example you are charging a battery, you can observe the charge status at that moment. Another advantage of this circuit, when the drawn current exceeds 1A (practically 0.85A), the current protector in LM317….(design added 11/08)

1.5V LED Flasher Version A - Many published circuits that flash LEDs need 3 volts or more. This circuit uses only a single inexpensive C-MOS IC and flashes the LED for a full year on a single 1.5 volt AA alkaline battery cell. The circuit uses a charge pump technique to provide the LED the needed voltage. ….(designed by David A. Johnson)

1.5v LED Flasher Version B - To squeeze even more energy from a alkaline battery cell, this circuit adds two transistors to a circuit similar to the above design to boost the efficiency. A small 1.5-volt alkaline N cell should flash the LED for a full year. It too uses a "charge pump" technique to provide a LED the needed voltage. ….(designed by David A. Johnson)

12 Volt Lead Acid Battery Monitor - This simple circuit makes it possible to monitor charging process to a higher level. (Tony van Roon's electronic design added 4/02)

120 & 240Vac LED Voltage Indicator - Useful for power lines control. Simple, transformerless circuitry (added 2/07)

120vac/240vac Indicator - Two LEDs indicate if a power line has 120vac or 240vac voltage on it. (added 7/06) ….(designed by David A. Johnson)

125kHz Wireless Smart Key Detector - This circuit will turn on an indicator light whenever it detects a smart car key containing an RFID chip. (added 7/06) ….(designed by David A. Johnson)

12v Lamp Current Indicator - This circuit turns on a LED indictor light whenever DC current flows into a 12v lamp. (added 7/06) ….(designed by David A. Johnson)

2 Cell Lithium Ion Battery Charger - This circuit was build to charge a couple series Lithium cells (3.6 volts each, 1 Amp Hour capacity) installed in a portable transistor radio. The charger operates by supplying a short current pulse through a series resistor and then monitoring the battery voltage to determine if another pulse is required. The current can be adjusted by changing the series resistor or adjusting the input voltage....(electronic diagram added 6/06)

2 Line Telephone Line Status Indicator - Many home businesses use multiple phone lines. This circuit gives you a visual indication when a line is in operation. The two AA battery cells should provide enough power for about one year of operation. The circuit is line polarity insensitive. ….(designed by David A. Johnson)

3 Level Audio Power Indicator - Battery-operated3 LED display that connect it to loudspeaker output (added 04/02)

3 Volt Low Battery Voltage Flasher - This circuit is designed to monitor two alkaline cells (3v) that form the battery often used in portable electronic equipment. It use an inexpensive IC from Panasonic that is connected to an efficient LED flashing circuit. When the battery voltage drops below a certain point the circuit flashes the LED. In the off state the circuit draws only 1uA, while in the active flashing state it draws 20uA. Published in EDN, Jan 2, 1997 ….(designed by David A. Johnson)

4 & 8 Infrared-Proximity Detectors (TSOP4830) - In this circuit the TSOP4830 is used as a sensitive infrared detector that does not require shielding from room lighting. The detector will work under almost any lighting condition from complete darkness to full sunlight….(added 08/08/08)

4 Line Telephone Line Status Indicator - Many home businesses use multiple phone lines. This circuit gives you a visual indication when a line is in operation. The two AA battery cells should provide enough power for about one year of operation. ….(designed by David A. Johnson)

50 MHz Frequency Counter Voltage Meter & SwR/PWR Indicator - This is a successor of the PIC16C71 4-digit LED f-counter & V-meter. Some hard to find parts used in the previous version, which are out of production for some time, has been omitted. A rather early PIC16C71 has also been replaced by 28-pin device PIC16F876....(electronic diagram added 6/03)

AC Current Indicator Light - This circuit could be wired into a 120vac power line, which feeds power to any load, ranging from 40 watts to 250 watts. It will turn on a LED light whenever current is being drawn by a load. It is especially useful for remote lights, where you may not be able to see if the lamps are receiving power. ….(designed by David A. Johnson)

Acceptable Voltage Indictor - I have used this circuit many times in custom test fixtures where a simple go-no go indication was needed. The circuit can also be used to adjust a particular voltage be within specific high or low limits. The three LEDs will indicate if the voltage is high, low or OK. When connected to other converters, such as a frequency to voltage converter, a current to voltage converter or a power to voltage meter, it could provide a quick indication of a proper level. ….(designed by David A. Johnson)

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

Audio Indicator - This circuit can be used to remotely monitor a loudspeaker, alarm, or audio source for presence of an audio waveform. It can also be directly connected across loudspeaker terminals used as a peak indicator.
….(electronic design added 6/07)

Audio Level Indicator - Audio Amplifier output relay delay (added 5/03)

Audio Visual Indicator for Telephones - Many a times one needs an extra telephone ringer in an ad joining room to know if re is an incoming call. For example, if telephone is installed in drawing room you may need an extra ringer in bedroom. All that needs to be done is to connect given circuit in parallel with existing telephone lines using twin flexible wires. This circuit does not require any external power source.... (added 11/06)

Audio Volume Indicator - uses an XS40 Board and XStend Board to display volume of an audio input on a barograph LED. (added 5/03)

Automotive 12v Electrical System Voltage Indicator - This battery powered unit is designed to quickly aid troubleshooting of 12v electrical systems in a car. Three LEDs proved a visual indication of a +12v, ground or an open circuit voltage level. Posted ….(designed by David A. Johnson)

Automotive Electrical Voltage Indicator - This circuit will indicate if an automotive electrical circuit has zero volts or 12 volts present. (added 7/06) ….(designed by David A. Johnson)

Automotive Speed Indicator - The speed of an automobile can be indicated by detecting the pulses generated by the ignition system and causing an LED to light. The circuit utilizes a quad NOR gate IC chip. Two of the gates are configured as a one shot multivibrator ….(added 08/08/08)

Automotive Voltage Indicator - Monitors battery voltage, Three-LED Display (circuit added 6/07)

Bad Light Bulb Indicator - This request came from a Discover Circuits visitor. He wanted to turn on a LED indicator light whenever a circuit detected a burned out tail/brake light on a car or truck. The circuit shown below uses a transistor switch, to detect current flowing through a low value resistor. If current is flowing to a light bulb, the circuit shunts current around a LED light, keeping the LED turned off. If there is no current detected, the LED turns on. The circuit should operate from 6v to 24v.... ….(designed by David A. Johnson)

Battery Charge Current Indicator - This circuit turns on a LED whenever it detects at least 25ma of battery charge current. (added 7/06) ….(designed by David A. Johnson)

Battery Chargers Indicates Rate of Charge - 05/25/95 EDN-Design Ideas: A single LED indicates wher battery Chargers s delivering a trickle charge or a fast charge, circuit designed to charge2-14 cells.....(design idea added 4/02)

Battery Equal Charge Indicator - The circuit below illuminates an LED to indicate unequal charges between two 12 volt lead batteries. It can be used to verify that two batteries are connected in parallel or isolated since the LED will be off when the voltages are equal within a tollerance, or on if the voltage difference is greater than 100 millivolts. Three comparators....(electronic schematic / circuit added 04/03/02)

Battery Monitor Emulates Auto Dashboard - 07/03/97 EDN-Design Ideas: When you use battery-powered scientific-recording equipment, you must know the state of the battery, because an unnoticed battery run-down can lead to loss of data. Several types of warning indicators are available, but all have their drawbacks. Moving-coil indicators, test terminals, and digital flags, for example,.....(design idea added 3/03)

Bi-Color LED Indicates Power/Fault - EDN 12/05/96 Single LED indicates both power on and blown-fuse conditions. (added 9/04)

Blown Fuse Indicator - (electronic Circuit / Schematic added 10/04)

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