| RSS Web Feed for Renewable Energy UK | REUK Shop | Bookmark Site | About Us  

LM741 OpAmp Voltage Indicator



LM741 OpAmp Voltage Indicator

Plans for a simple voltage high/low indicator built around an LM741 operational amplifier

electronics | electric circuit | general
Printer Friendly Version Print Article     

We have previously published articles* describing electric circuits which can be used to indicate when the voltage of a power source (for example, a battery bank) either reaches a certain point, or falls below a certain point.
* Read Make a Simple Battery Status Monitor, TL431 Battery Voltage Monitor.

This article will introduce plans for a voltage status monitor built around the LM741 operational amplifier. These circuits are the best we have found in terms of accuracy, simplicity of operation, and cost.

LM741 Operational Amplifier


LM741 Operation Amplifier integrated circuit

The LM741 is an operational amplifier. The wide range of uses of this simple and cheap integrated circuit do not need to be mentioned here - of importance is that an output voltage is turned on (or off) automatically when a measured voltage (e.g from a battery) reaches the same value as a reference voltage (manually set by the user).

Therefore, if we want an LED to light up when a solar battery charger reaches a certain voltage for example, we can achieve this with an LM741.
You can buy the LM741 in the REUK Shop.

The LM741 specification sheet can be downloaded here.

LM741 High Voltage Indicator


LM741 Op Amp High Voltage Indicator Circuit Diagram

The circuit diagram shown above is configured to give a high voltage indication. The 100KOhm variable resistor is used to manually configure the voltage over and above which the LED will light. If the voltage arriving at pin 2 of the LM741 is greater than the voltage arriving at pin 3, the LED lights thanks to the output from pin 6. At all other times the LED is off (as is the output from pin 6).

The Zener diode should be chosen with a zener voltage of around half that of the target voltage - e.g. for a 12.0 Volt indicator, a 5.6 Volt Zener diode could be used.

LM741 Low Voltage Indicator


LM741 Op Amp Low Voltage Indicator Circuit Diagram
In order to obtain a low voltage indication - useful if you would like to stop using a battery before it is drained too deeply - the output from pin 6 is still directed through an LED (and current limiting resitor), but this time it is connected to ground rather than to the input voltage Vin as shown in the amended circuit diagram above.

Note that this circuit will only operate with input voltages in excess of around 3.8 Volts and so it cannot be used with a 2 AA battery charger.

NEW For an LM741-based circuit plan for a low voltage indicator specifically for a typical 12 Volt battery or battery bank, click here to read our article 12 Volt Low Battery Indicator - LM741.

Configuring the Voltage Indicator

In order to set up the voltage indicator a variable voltage source should ideally be used. Using a digital multimeter set the voltage to the desired light up LED value, connect the voltage source to the circuit, and then turn the 100K variable resistor until the LED is just turning on/off. It is now configured to light up (or turn off) the LED at that exact voltage.

If you do not have a variable voltage source - as is the case for most people - then you need to find a way to supply the desired reference voltage to the circuit for configuration. If for example, you want to light up the LED when a solar battery charger has fully charged some batteries, connect fully charged batteries to the solar panel and then connect the whole thing to the circuit while you adjust the 100K variable resistor.
Similarly if you want the LED to light up when a 12V lead acid battery is 25% discharged (i.e. you measure a terminal voltage of 12.00V on the battery), then wait until your battery has discharged approximately this far and then set up the indicator circuit.

Article Last Modified: 09:31, 8th Oct 2007


Recommended Related Articles

People who read this article also enjoyed the following articles:

12 Volt Battery Low Indicator LM741
Plans for a battery low indicator for a 12 Volt battery using an LM741 operational amplifier
Article Last Modified: 10:17, 28th Jul 2007
electronics | electric circuit | general

Make a Simple Battery Status Monitor
Monitor battery status with this easy electric circuit project - no skill required!
Article Last Modified: 12:33, 16th Mar 2007
storage | electric circuit

LM741 Light Dark Sensor Circuit
Build a light/dark sensing circuit to automatically turn on/off lights and other devices
Article Last Modified: 08:43, 2nd Nov 2007
electronics | electric circuit | general

TL431 Battery Voltage Monitor
Monitor the voltage of a battery or battery bank using an TL431 (aka LM431) shunt regulator
Article Last Modified: 16:42, 11th Jun 2007
storage | electric circuit | electronics

Zener Diode Voltage Regulator
Make a simple zener diode voltage regulator
Article Last Modified: 17:31, 7th Mar 2008
electric circuit | education

LM317 Current Calculator
A handy online output current calculator for the LM317, LM338, and other linear voltage regulators
Article Last Modified: 12:47, 12th Mar 2008
electric circuit | electronics | general

Basic 4 AA Solar Battery Charger Plans
Make a simple solar charger for 4 AA rechargeable batteries
Article Last Modified: 09:43, 30th Jul 2007
solar | education

Voltage Doubler for Solar Battery Charger
Boost the voltage of a solar panel to power higher voltage devices or charge batteries
Article Last Modified: 13:15, 16th May 2007
solar | electronics | education

LM317 Voltage Calculator
A handy online output voltage calculator for the LM317, LM338, and other linear voltage regulators
Article Last Modified: 12:47, 12th Mar 2008
electric circuit | electronics | general

High Capacity Alternative to 9 Volt Battery
Get ten times the capacity of a 9 Volt battery to power your devices
Article Last Modified: 09:39, 7th Jun 2008
general | electric circuit | solar

© 2006-2008 REUK - All Rights Reserved
Page Last Updated on 21st August 2008 at 01:08:27pm

Latest
Articles


40 Amp Blocking Diode 1N1190A
Find out how to use a blocking diode with a wind turbine generator
wind
13:36, 20th Aug 2008

La Rance Tidal Power Plant
Find out La Rance experimental tidal power plant in France
tidal
15:32, 19th Aug 2008

PVC Wind Turbine Blades
Learn how to make your own PVC wind turbine blades
wind
15:16, 19th Aug 2008

Shed and Garage Solar Lighting
Light your shed or garage with solar powered lighting
lighting
15:16, 19th Aug 2008

How I Built A Wind Turbine
Read how a wind turbine was built for under US$150
wind
15:16, 19th Aug 2008

10 Ways to Save Water
Find out how you can save water, energy, and money
water
15:16, 19th Aug 2008

Rainwater Toilet Flush System
Find out how to put together a complete rainwater fed toilet flushing system
water
15:16, 19th Aug 2008

Jatropha for Biodiesel Figures
Look at the financial costs of commercial Jatropha growing for Biodiesel
biomass
15:16, 19th Aug 2008



REUK Shop

Popular Items


KILL A WATT
Plug in Mains Power and Energy Monitor
£19.99 each.
Energy Saving



EFERGY HOMECO2METER
efergy homeCO2meter wireless electricity monitor
£38.99 each.
Energy Saving



240V LED SPOTLIGHT BULB
240V LED GU10 bulb. 20 x 20,000mcd white LED 1 Watt bulb
£4.99 each.
Energy Efficient Lighting



RAINWATER DIVERTER KIT
Rainwater diverter kit for standard plastic 65mm square and 68mm round downpipes
£8.99 each.
Water Conservation



300 WATT POWER INVERTER
Convert 12V DC battery power into 230 AC to power portable televisions, computers, video recorders etc. 300 Watt power rating - peak power 600 Watts
£29.99 each.
Renewable Energy System Parts



12 VOLT 3 WATT SOLAR PANEL
Waterproof 12 Volt 3 Watt Solar Panel - 199 x 136mm with fitted leads (fiberglass and resin).
£19.99 each.
Solar Power



SUNGUARD SOLAR CONTROLLER
4.5 Amp at 12 Volt solar charge controller - fully encapsulated and weatherproofed
£19.99 each.
Solar Controllers