Voltage Detectors / Sensors / Monitors Electronic Circuits


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Voltage Detectors / Sensors / Monitors
Last Updated on: Friday, April 25, 2008 04:35 AM

Sensors / Detectors -- Main Page

Circuits Designed by Dave Johnson, P.E. :

9v Battery Voltage Monitor
This circuit turns on a LED whenever the voltage of a standard 9v battery connected to the circuit drops below 7.2 volts. It uses a LTC1440 comparator, which also contains a 1.18v reference diode. In standby mode, the circuit draws only 4uA. (added 7/06)

Acceptable Voltage Indicator
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.

Low Battery Voltage Flasher
This circuit is designed to monitor two alkaline cells (3v) that from 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

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

AN779: Using the Microchip TC54 Voltage Detector: Microchip Application Note Published 12-Nov-02 (app note added 2/06)

Battery Monitor Draws 8 µor Less: 04/13/95 EDN-Design Ideas / (added 3/03)

Battery Monitor Emulates Auto Dashboard: 07/03/97 EDN-Design Ideas / (added 3/03)

Circuit Detects and Disconnects OverVoltages: 04/25/96 EDN-Design Ideas / (added 3/03)

Circuit Detects total OnTime: 02/04/99 EDN-Design Ideas / (added 8/03) The circuit in Figure 1 provides a voltage that is directly proportional to the sum of the total on-times for a number of positive pulses that occur during the interval between sample signals. When a positive R2, which drives Q1's gate at C1's potential. C1 and C2 should be noninductive and have low dielectric absorption.....

Circuit Detects Voltage over Ranges: 10/10/96 EDN-Design Ideas / (added 3/03)

Circuit Disconnects Load from Battery: 03/14/96 EDN-Design Ideas / (added 03/03)

Circuit Provides 15V 7Bus Termination: 09/14/95 EDN-Design Ideas / (added 3/03)

Circuit safely applies Power to ICs: 11/22/01 EDN Design Ideas / (added 1/05) Supervisory circuits normally monitor a microprocessor's supply voltage, asserting reset to the IC during power-up, power-down, and brownout. In this way, the circuit ensures that the supply voltage.....

Clamping circuit dissipates minimal power: 03/30/00 EDN-Design Ideas / (added 5/02) /This circuits is a quasi-linear regulator

Cockcroft Walton Diode Voltage Multipliers: this document describing some basic voltage multiplier circuit topologies, PDF file (added 5/02)

Comparator detects failed telecomm supplies: 06/22/00 EDN-Design Ideas / (added 5/02) / Detects when telecomm power supplys48V output drops below its nominal value, uses an isolated comparator to monitor two48V telecomm supplies (of either polarity) / PDF contains multiple circuits scroll to find the one of interest

Contactless AC Mains Voltage Detector: (electronic Circuit / Schematic added 10/04)

DC Power Supply: simple circuit based on 78xx fixed voltage regulator IC, those ICs are available for some fixed voltages between5 and24V (added 5/02)

Latching Regulator Prevents Deep Discharge: 03/16/95 EDN-Design Ideas / (added 03/03)

Low Voltage Alarm: NE555 Low Voltage Battery Disconnect Circuit (added 5/02)

Maximum Voltage Sorter uses Analog Multiplexers: 09/29/94 EDN-Design Ideas / (added 3/03) The voltage-sorting circuit in Fig 1 continuously finds the maximum of eight input voltages and the corresponding binary address with the aid of two analog multiplexers, IC1 and IC2. The circuit compares each input sequentially with the current maximum voltage and updates the maximum voltage....

Microprocessor supervisor and regulator form in range Voltage monitor: 06/10/04 EDN Design Ideas / (added 1/05) Microprocessor supervisors reset controllers when power-supply voltages fall below given levels. As added protection, you can also reset the microcontroller when the power supply ....

OpAmp Rectifier Signals Input State: 07/21/94 EDN-Design Ideas / (added 3/03) 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....

Regulator IC forms convenient overVoltage detector: 09/28/00 EDN Design Ideas / (added 6/06)

Simple Circuit Detects Voltage over Ranges: 10/10/96 EDN-Design Ideas / (added 3/03)

Simple Circuit Disconnects Load from Battery: 03/14/96 EDN-Design Ideas / (added 03/03)

Solid State Relay Saves Battery's Life: 09/01/94 EDN-Design Ideas / (added 5/02) The circuit in Fig 1 uses a low-resistance p-channel FET, Q4, to disconnect a load from the battery when the battery's voltage drops below a certain value. After you disconnect the circuit, it remains off until you remove and replace the battery.

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.....

Supervisory IC Makes Simple Line Monitor: 03/01/96 EDN-Design Ideas / (added 03/03)

Using the Microchip TC54 Voltage Detector: Microchip Application Note Published 12-Nov-02 (app note added 2/06)