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Voltage Detectors / Sensors / Monitors
#'s - B      C - D      E - M      N - V
Sensors / Detectors -- Main Page
Last Updated on: Friday, October 17, 2014 06:58 AM

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.

Links to electronic circuits, electronic schematics, designs for engineers, hobbyists, students & inventors:
“Hippasian” nonlinear VFC stretches dynamic range -  19-Feb-09 Issue of EDN  A voltage-to-frequency converter uses square roots to extend dynamic range by orders of magnitude.... [Design Idea by W Stephen Woodward, Chapel Hill, NC]
3 Digits Digital Volt Meter with PIC16F676 -  This is simple 3-digits digital volt meter.PIC16F676 used to read analog signal(voltage) and display the value on 3-digits 7-segment. You can apply similar principles to measure DC current with parallel R shunt. …....
3 Level Audio Power Indicator -  Battery-operated3 LED display that connect it to loudspeaker output (added 04/02)
3-Digit DVM Voltmeter -  Uses 3161, CA3162 ICs ….(design added 11/08)
3-Digit Volt/ Amper Meter -  Even if the digital multimeters have dominated in a lot of applications, in the measurement, exist the need for existence of instruments of clue in various appliances, voltage and current, …....

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.... [Hobby Corner Circuit by Dave Johnson]
AC Line Under/Over Voltage Alarm -  Power lines, which deviate much beyond normal voltages can damage expensive electronic equipment.  The circuit below sounds an alarm whenever the line voltage is higher or lower than normal.  I set the alarm limits at about +-15% from standard levels.  The circuit rectifies and filters the power line signal.  I set the resistor values, so the DC voltage produced is close to 1% of the RMS value of the line.  Thus, a 120vac line would yield about 1.2v DC.  That voltage is fed to a pair of voltage comparators.  The outputs of the comparators decide if the sampled voltage is above, below or acceptable.... [Designed by David A. Johnson]
AC Voltmeters & ammeters -  Electronic Circuit design (added 02/05)
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]
AN557: Four Channel Digital Voltmeter with Display & Keyboard -  Microchip Application Note Published 27-May-05  (app note added 2/06)
AN779: Using the Microchip TC54 Voltage Detector -  Microchip Application Note Published 12-Nov-02  (app note added 2/06)
Analog Milliamp Meter Used as Voltmeter -  A milliamp meter can be used as a volt meter by adding a series resistance. The resistance needed is the full scale voltage reading divided by the full scale current of the meter movement. So, if you have a 1 milliamp meter and you want to read 0-10 volts you will need a total resistance of 10/.001 = 10K ohms. The meter movement itself will have a small resistance.... [Bill Bowdewn's site]
AVR Digital Voltmeter -  Most electronics hobbyists these days find a digital voltmeter indispensable. Indeed, having more than one is a positive advantage!This little project with six voltmeters in one inexpensive box therefore has some very useful features for the hobbyist. The unit is quite inexpensive, two ICs and a couple of transistors. One of the ICs is an AT90S4433 AVR..(electronic circuit added 4/05)
Ballantine 300 AC Voltmeter manual w/schematic -  (manual added 07/07/07)
Battery Monitor Draws 8 µor Less -  04/13/95 EDN-Design Ideas....The battery monitor in Fig 1 nominally draws 5 µA during normal operation and flashes an alarm indicator when the battery voltage drops below a critical value. The alarm-state current depends on the desired indicator brightness, but you can easily make the current average less than 500 µA.  This monitor was developed as a change-battery warning.... [Design Idea by Arthur W Du Rea Jr, Science Applications International Corp, Oak Ridge, TN]
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 by TG Barnett and J Millar, University of London, UK]

Voltage Detectors / Sensors / Monitors:   #'s - B      C - D      E - M      N - V

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