Low Voltage Alarm

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This low voltage circuit can be used to monitor batteries and other volatile sources of current for problems. The circuit sounds an alarm and lights an LED, but can be interfaced to any number of other circuits for many different uses.

Schematic

Parts

Part	Total Qty.	Description	Substitutions
R1, R3	2	1K 1/4W Resistor
R2	1	5K Pot
U1	1	LM339 Op Amp IC
D1	1	1N5233B Zener Diode
D2	1	LED
BZ1	1	Piezo Buzzer
MISC	1	Board, wire, socket for IC

Notes

The circuit will operate from 9V to 12V.

Adjust R2 until the alarm goes off at the correct voltage.

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Comments

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Kashinath Low Voltage cut off circuit at 3V for 1A load current Friday, November 15, 2013 12:12:19 AM

hi everyone.. I need to provide battery back up facility to my one project. so for that purpose i used Li-ion battery(Max 4.2V/ 1A) to provide the supply to load. so i need to cut off the load at 3V. can i use above circut for that purpose?? please anyone help me. Thanks in advances

saurabh Low Voltage Alarm Tuesday, May 01, 2012 10:42:02 AM

where do we give the i/p and take the o/p and i hve a 9V battery and 12V zener would it work

anonymous Low Voltage Alarm Wednesday, January 04, 2012 1:44:37 PM

What if I have a 12 volt battery and want it to alarm me when it drops to say 9 to 10 volts. How does this work?

bhanu pp Low Voltage Alarm Monday, April 18, 2011 1:19:29 PM

nice ckt

Doug Low Voltage Alarm Tuesday, March 01, 2011 8:51:26 PM

Substituted a HA17339 for the LM339, used a 6.2V zener, a 2.2V (green) LED and a 6K POT. Left out the piezo buzzer. The circuit works like a charm.

ARSALAN AFRIDI electronics Thursday, December 23, 2010 2:40:39 AM

AOA I WANT CONSTRUCT THE WATER FLOW ALARM CIRCUIT SO PLZ KINDLY HELP ME ABOUT THIS PROJECT ME WAITING OF YOUR REP AND PLZ SEND THE DEMO CIRCUIT FOR TH E IDEA ,,, THANK YOU DEAR

Prash Low Voltage Alarm Friday, April 16, 2010 3:25:43 PM

Nice project..it works perfect..Thank u!

Taylor Low Voltage Alarm Friday, March 12, 2010 8:27:35 AM

The schamatic I downloaded had the Zener backwards and the LED stayed on. Turned around and worked great. Made another on for my neighbors stored RV battery. Thanks

Terry Low Voltage Alarm Sunday, January 31, 2010 8:37:43 PM

hi, i cannot get a 6v zener diode in New Zealand, will a 5.6v or a 6.2v work instead?

Ritesh Agarwalla Low Voltage Alarm Thursday, December 10, 2009 9:21:30 AM

I am planning to trigger the 12V Cutout at 11V so please suggest me the alternative for 5k pot.

Amol Raskar l. Low Voltage Alarm Saturday, September 19, 2009 3:18:59 PM

I implement above circuit, but problem with that is I didn't know how it operates? give me working operation of low voltage alarm . how it operates between 9 to 12 volt & when LED glow? please give description .

EDC Electrical Designer Low Voltage Alarm Friday, July 17, 2009 1:40:56 PM

Yes, this product design is used in most schematic designs, but this isn't common, and therefore may not get that many views.

Thrasher Low Voltage Alarm Monday, June 08, 2009 4:46:02 PM

What is the formula used to determine effective range of the detector? I would like to have it sound the buzzer at 6v. Thank you for your help.

Arnold Baker Low Voltage Alarm Sunday, May 10, 2009 9:49:17 PM

Where do I find the parts? Specifically, the buzzer.

anonymous Low Voltage Alarm Wednesday, April 22, 2009 8:11:00 AM

from where i can find the data sheet of "LM 339"???/
(Editor's notes: Try Googling "datasheet LM339".)

luke bowman Low Voltage Alarm Tuesday, September 30, 2008 5:23:40 AM

its crap

netpower8 Low Voltage Alarm Monday, August 25, 2008 12:15:34 PM

Thanks for this circuit tried it and it works.. replaced it with a different ic and it works also. wil use this circuit if i get the 12v low battery cut-off circuit to work. will use this as a low batt warning bleeper... thanks again

kuja Low Voltage Alarm Sunday, March 16, 2008 3:05:35 PM

please give me introduction about low voltage alarm?send to my e mail...

kuja Low Voltage Alarm Sunday, March 16, 2008 2:52:58 PM

i want to have the circuit operation of the low voltage alarm and the it's output waveform immediately...and also i want to know what is the low voltage alarm?oscillator or 555 timer?

anonymous Low Voltage Alarm Wednesday, February 06, 2008 9:16:20 AM

i want the Pcb lay-outs of low voltage alarm

anonymous Low Voltage Alarm Monday, January 21, 2008 7:39:08 PM

What value resistor would I need to use to replace the 5k pot so it will trigger at 11V? I am trying to make it a little lighter and smaller. Thanks

anonymous Low Voltage Alarm Saturday, December 08, 2007 12:27:14 PM

4mv/100c 140 degrees C is when I want it to trigger so about 6 mv i need it to trigger a relay

anonymous Low Voltage Alarm Saturday, December 08, 2007 12:16:37 PM

I'm looking to make a shutdown switch for a truck. Using a very low voltage coming from the exhaust thermocouple. What modifications to this circuit should I make. I think the voltage is less than .5volts and a very small range to the desired shutdown

nylAdOhr Low Voltage Alarm Wednesday, November 28, 2007 8:02:12 PM

.im interested in this kind of project.. please send me more info. and i want to know if i need to make some adjustments for it to work. please...

cuting man Low Voltage Alarm Wednesday, November 21, 2007 10:23:28 AM

the circuit not working why ?

anas Low Voltage Alarm Tuesday, November 20, 2007 11:53:35 AM

it woks

me Low Voltage Alarm Tuesday, November 20, 2007 4:03:43 AM

we want more info. on low voltage indicators simply....

ted Low Voltage Alarm Monday, November 19, 2007 4:43:42 AM

please i want to have the circuit operation of the low voltage alarm

H�kan Low Voltage Alarm Thursday, November 08, 2007 3:40:42 PM

Emanuela. The voltage reference zener diode (D1 1N5233B ) specified is at 6V so it should just work. However, if you need to have exactly 6V you might want to be able to adjust a bit. Replace D1 with a zenerdiod at around 5V instead. /H�kan

emanuela Low Voltage Alarm Tuesday, November 06, 2007 9:33:05 AM

I wold like to buil a low voltage alarm that can test 6V output. Can I use your circuit or I need to make some adjustment. Please let me know

H�kan Low Voltage Alarm Saturday, October 20, 2007 1:06:57 PM

Working OK. The plus and minus sign is switched though but the pin assignment is OK. I.e connecting it as the circuit is drawn following the pin assignment will work. The explanaition of the ciruit in short is. As long as the voltage is higher on pin 5, higher = to the zener voltage of the zener diod (6V), the output, 2 will be high = buzzer will NOT sound. When the voltage on pin 5 get lower then pin 4 the output, pin 2 will go low = buzzer WILL sound. The voltage when to have the buzzer to sound is adjustable by the trim pot.

H�kan Low Voltage Alarm Friday, October 19, 2007 1:30:35 PM

The pin 4 and 5 in the drawing is mixed up. Plus is 5 and minus is 4

fazi Low Voltage Alarm Thursday, October 04, 2007 3:26:40 AM

give some research for low voltage alarm and introduction for this proj send in my email..and i want to know which programme you use to draw the circiut.. i waiting for the reply.ASAP.thanks you very much!!!

Bhenne Low Voltage Alarm Tuesday, September 18, 2007 7:00:32 PM

we're trying to make some project, and we want to explore more about this low voltage alarm, can you please help us. Please send more information, thank you.

MABILA SAKHI Low Voltage Alarm Saturday, September 15, 2007 4:52:06 AM

Hi Sir/ Msdam Give some research for low voltage alarm and introduction for this proj send in my email...I want voltage variation alarm from less than 100 volts a.c . domestic supply is 220 V a.c ,,,,,,,,,,, thank you very much!!!

Hazrat hilal Low Voltage Alarm Tuesday, September 04, 2007 1:03:59 AM

can you tell me about factory siren with heavy sound system please mail me Thanks !

tec Low Voltage Alarm Friday, August 31, 2007 12:10:13 PM

any changes for 7.4 voltage lipo

prem Low Voltage Alarm Wednesday, August 29, 2007 6:34:07 AM

give some research for low voltage alarm and introduction for this proj send in my email... i want voltage variation alarm from less than 150 volts a.c . domestic supply is 220 V a.c ,,,,,,,,,,, thanks you very much!!!

marees Low Voltage Alarm Tuesday, August 28, 2007 12:54:37 AM

i like your little circuit,but i want clear explanation about LVA

vansh Low Voltage Alarm Wednesday, August 22, 2007 3:40:14 AM

Op-amp ic used in this circuit has 5-terminals, while ic which one we bought has 14 pins. pls help us to know which pins are to be used as these terminals.

marvin leo de vera Low Voltage Alarm Monday, August 13, 2007 12:56:10 PM

give some research for low voltage alarm and introduction for this proj send in my email... thanks you very much!!!

anonymous Low Voltage Alarm Friday, July 20, 2007 3:52:41 AM

Hey I want this circuit to control a relay switch with hysterisis. How can I do this. Dennis

sehrish Low Voltage Alarm Friday, June 29, 2007 6:50:39 AM

it has no complete detail

Phil Low Voltage Alarm Thursday, June 21, 2007 9:03:53 PM

Can U tell me how to adapt the circuit to 36V for a golf cart to alarm when battery is getting low. I will also need a time delay circuit as voltage might drop for 30 seconds or so going up hill.

John Brown Low Voltage Alarm Thursday, June 14, 2007 10:55:15 AM

can this circuit be modified to be applied to a 220v 3ph power supply, if yes can you give detail on the circuit.

Daniel Low Voltage Alarm Monday, May 28, 2007 8:01:01 AM

please i wanna do something on this, hope its reliable?

basiru Low Voltage Alarm Thursday, May 24, 2007 6:40:04 AM

complete explanation on it and how it's works.

Raj Low Voltage Alarm Friday, May 18, 2007 4:40:39 AM

This looks very well, can you pl tel me Zener diode value for +24 V

syaiful Low Voltage Alarm Thursday, May 10, 2007 10:04:19 PM

hey!!...i'm totally new about electronics and i have a project on exactly this low voltage alarm but we have to add in sensors..can u actually, kindly advise me what are the things and how to set up the circuit...?..i wud appreciate ur help..Thankz... :)

ahmed algheilania - oman-sur Low Voltage Alarm Wednesday, May 09, 2007 5:45:25 PM

can i have the working of this circuit

lui Low Voltage Alarm Tuesday, May 08, 2007 10:49:04 AM

Hey I like the circuit. Could you give me details on exactly how this circuit works and any other info regarding it. Also if I wanted to change the voltage being inputted in to around 6V, what necessary changes will I have to make to the circuit and where? Thanks

anonymous Low Voltage Alarm Wednesday, April 04, 2007 9:58:04 PM

how to make circuit and discrimsion about syambol use in it

vinay Low Voltage Alarm Friday, March 23, 2007 10:21:15 AM

please give me some help how to realize it ..can it realize on a single breadboard..and give how it works..thanx

anonymous Low Voltage Alarm Tuesday, March 20, 2007 10:08:13 PM

nice one!!^-^

Emmanuel E Low Voltage Alarm Thursday, March 08, 2007 8:03:52 PM

please l will like to ask for your help to enable me or guild me in the production of this low voltage alam,because am writing a project on this.thanks

lou Low Voltage Alarm Wednesday, February 28, 2007 4:48:18 PM

Hi , I send you a comment and some qoues. but I didn't realize I can put my e-mail. My Qoue. is again can I use this device to test skin Voltage ? I am still trying to build a Seizure Alert Device in conjuction with voltage measurment of the person skin .

anonymous Low Voltage Alarm Wednesday, February 28, 2007 4:15:38 PM

Hey I like this one too ,but can I use it to measure skill voltage of a person? I am still to construct seizure Alert Device by combining different componnets.

Will Low Voltage Alarm Wednesday, February 28, 2007 3:58:13 PM

Hello I like your little circuit. I would like to know if it could be mod. so the led would light when a cap reaches a set voltage.

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Kashinath	Low Voltage cut off circuit at 3V for 1A load current	Friday, November 15, 2013 12:12:19 AM
hi everyone.. I need to provide battery back up facility to my one project. so for that purpose i used Li-ion battery(Max 4.2V/ 1A) to provide the supply to load. so i need to cut off the load at 3V. can i use above circut for that purpose?? please anyone help me. Thanks in advances
saurabh	Low Voltage Alarm	Tuesday, May 01, 2012 10:42:02 AM
where do we give the i/p and take the o/p and i hve a 9V battery and 12V zener would it work
anonymous	Low Voltage Alarm	Wednesday, January 04, 2012 1:44:37 PM
What if I have a 12 volt battery and want it to alarm me when it drops to say 9 to 10 volts. How does this work?
bhanu pp	Low Voltage Alarm	Monday, April 18, 2011 1:19:29 PM
nice ckt
Doug	Low Voltage Alarm	Tuesday, March 01, 2011 8:51:26 PM
Substituted a HA17339 for the LM339, used a 6.2V zener, a 2.2V (green) LED and a 6K POT. Left out the piezo buzzer. The circuit works like a charm.
ARSALAN AFRIDI	electronics	Thursday, December 23, 2010 2:40:39 AM
AOA I WANT CONSTRUCT THE WATER FLOW ALARM CIRCUIT SO PLZ KINDLY HELP ME ABOUT THIS PROJECT ME WAITING OF YOUR REP AND PLZ SEND THE DEMO CIRCUIT FOR TH E IDEA ,,, THANK YOU DEAR
Prash	Low Voltage Alarm	Friday, April 16, 2010 3:25:43 PM
Nice project..it works perfect..Thank u!
Taylor	Low Voltage Alarm	Friday, March 12, 2010 8:27:35 AM
The schamatic I downloaded had the Zener backwards and the LED stayed on. Turned around and worked great. Made another on for my neighbors stored RV battery. Thanks
Terry	Low Voltage Alarm	Sunday, January 31, 2010 8:37:43 PM
hi, i cannot get a 6v zener diode in New Zealand, will a 5.6v or a 6.2v work instead?
Ritesh Agarwalla	Low Voltage Alarm	Thursday, December 10, 2009 9:21:30 AM
I am planning to trigger the 12V Cutout at 11V so please suggest me the alternative for 5k pot.
Amol Raskar l.	Low Voltage Alarm	Saturday, September 19, 2009 3:18:59 PM
I implement above circuit, but problem with that is I didn't know how it operates? give me working operation of low voltage alarm . how it operates between 9 to 12 volt & when LED glow? please give description .
EDC Electrical Designer	Low Voltage Alarm	Friday, July 17, 2009 1:40:56 PM
Yes, this product design is used in most schematic designs, but this isn't common, and therefore may not get that many views.
Thrasher	Low Voltage Alarm	Monday, June 08, 2009 4:46:02 PM
What is the formula used to determine effective range of the detector? I would like to have it sound the buzzer at 6v. Thank you for your help.
Arnold Baker	Low Voltage Alarm	Sunday, May 10, 2009 9:49:17 PM
Where do I find the parts? Specifically, the buzzer.
anonymous	Low Voltage Alarm	Wednesday, April 22, 2009 8:11:00 AM
from where i can find the data sheet of "LM 339"???/ (Editor's notes: Try Googling "datasheet LM339".)
luke bowman	Low Voltage Alarm	Tuesday, September 30, 2008 5:23:40 AM
its crap
netpower8	Low Voltage Alarm	Monday, August 25, 2008 12:15:34 PM
Thanks for this circuit tried it and it works.. replaced it with a different ic and it works also. wil use this circuit if i get the 12v low battery cut-off circuit to work. will use this as a low batt warning bleeper... thanks again
kuja	Low Voltage Alarm	Sunday, March 16, 2008 3:05:35 PM
please give me introduction about low voltage alarm?send to my e mail...
kuja	Low Voltage Alarm	Sunday, March 16, 2008 2:52:58 PM
i want to have the circuit operation of the low voltage alarm and the it's output waveform immediately...and also i want to know what is the low voltage alarm?oscillator or 555 timer?
anonymous	Low Voltage Alarm	Wednesday, February 06, 2008 9:16:20 AM
i want the Pcb lay-outs of low voltage alarm
anonymous	Low Voltage Alarm	Monday, January 21, 2008 7:39:08 PM
What value resistor would I need to use to replace the 5k pot so it will trigger at 11V? I am trying to make it a little lighter and smaller. Thanks
anonymous	Low Voltage Alarm	Saturday, December 08, 2007 12:27:14 PM
4mv/100c 140 degrees C is when I want it to trigger so about 6 mv i need it to trigger a relay
anonymous	Low Voltage Alarm	Saturday, December 08, 2007 12:16:37 PM
I'm looking to make a shutdown switch for a truck. Using a very low voltage coming from the exhaust thermocouple. What modifications to this circuit should I make. I think the voltage is less than .5volts and a very small range to the desired shutdown
nylAdOhr	Low Voltage Alarm	Wednesday, November 28, 2007 8:02:12 PM
.im interested in this kind of project.. please send me more info. and i want to know if i need to make some adjustments for it to work. please...
cuting man	Low Voltage Alarm	Wednesday, November 21, 2007 10:23:28 AM
the circuit not working why ?
anas	Low Voltage Alarm	Tuesday, November 20, 2007 11:53:35 AM
it woks
me	Low Voltage Alarm	Tuesday, November 20, 2007 4:03:43 AM
we want more info. on low voltage indicators simply....
ted	Low Voltage Alarm	Monday, November 19, 2007 4:43:42 AM
please i want to have the circuit operation of the low voltage alarm
H�kan	Low Voltage Alarm	Thursday, November 08, 2007 3:40:42 PM
Emanuela. The voltage reference zener diode (D1 1N5233B ) specified is at 6V so it should just work. However, if you need to have exactly 6V you might want to be able to adjust a bit. Replace D1 with a zenerdiod at around 5V instead. /H�kan
emanuela	Low Voltage Alarm	Tuesday, November 06, 2007 9:33:05 AM
I wold like to buil a low voltage alarm that can test 6V output. Can I use your circuit or I need to make some adjustment. Please let me know
H�kan	Low Voltage Alarm	Saturday, October 20, 2007 1:06:57 PM
Working OK. The plus and minus sign is switched though but the pin assignment is OK. I.e connecting it as the circuit is drawn following the pin assignment will work. The explanaition of the ciruit in short is. As long as the voltage is higher on pin 5, higher = to the zener voltage of the zener diod (6V), the output, 2 will be high = buzzer will NOT sound. When the voltage on pin 5 get lower then pin 4 the output, pin 2 will go low = buzzer WILL sound. The voltage when to have the buzzer to sound is adjustable by the trim pot.
H�kan	Low Voltage Alarm	Friday, October 19, 2007 1:30:35 PM
The pin 4 and 5 in the drawing is mixed up. Plus is 5 and minus is 4
fazi	Low Voltage Alarm	Thursday, October 04, 2007 3:26:40 AM
give some research for low voltage alarm and introduction for this proj send in my email..and i want to know which programme you use to draw the circiut.. i waiting for the reply.ASAP.thanks you very much!!!
Bhenne	Low Voltage Alarm	Tuesday, September 18, 2007 7:00:32 PM
we're trying to make some project, and we want to explore more about this low voltage alarm, can you please help us. Please send more information, thank you.
MABILA SAKHI	Low Voltage Alarm	Saturday, September 15, 2007 4:52:06 AM
Hi Sir/ Msdam Give some research for low voltage alarm and introduction for this proj send in my email...I want voltage variation alarm from less than 100 volts a.c . domestic supply is 220 V a.c ,,,,,,,,,,, thank you very much!!!
Hazrat hilal	Low Voltage Alarm	Tuesday, September 04, 2007 1:03:59 AM
can you tell me about factory siren with heavy sound system please mail me Thanks !
tec	Low Voltage Alarm	Friday, August 31, 2007 12:10:13 PM
any changes for 7.4 voltage lipo
prem	Low Voltage Alarm	Wednesday, August 29, 2007 6:34:07 AM
give some research for low voltage alarm and introduction for this proj send in my email... i want voltage variation alarm from less than 150 volts a.c . domestic supply is 220 V a.c ,,,,,,,,,,, thanks you very much!!!
marees	Low Voltage Alarm	Tuesday, August 28, 2007 12:54:37 AM
i like your little circuit,but i want clear explanation about LVA
vansh	Low Voltage Alarm	Wednesday, August 22, 2007 3:40:14 AM
Op-amp ic used in this circuit has 5-terminals, while ic which one we bought has 14 pins. pls help us to know which pins are to be used as these terminals.
marvin leo de vera	Low Voltage Alarm	Monday, August 13, 2007 12:56:10 PM
give some research for low voltage alarm and introduction for this proj send in my email... thanks you very much!!!
anonymous	Low Voltage Alarm	Friday, July 20, 2007 3:52:41 AM
Hey I want this circuit to control a relay switch with hysterisis. How can I do this. Dennis
sehrish	Low Voltage Alarm	Friday, June 29, 2007 6:50:39 AM
it has no complete detail
Phil	Low Voltage Alarm	Thursday, June 21, 2007 9:03:53 PM
Can U tell me how to adapt the circuit to 36V for a golf cart to alarm when battery is getting low. I will also need a time delay circuit as voltage might drop for 30 seconds or so going up hill.
John Brown	Low Voltage Alarm	Thursday, June 14, 2007 10:55:15 AM
can this circuit be modified to be applied to a 220v 3ph power supply, if yes can you give detail on the circuit.
Daniel	Low Voltage Alarm	Monday, May 28, 2007 8:01:01 AM
please i wanna do something on this, hope its reliable?
basiru	Low Voltage Alarm	Thursday, May 24, 2007 6:40:04 AM
complete explanation on it and how it's works.
Raj	Low Voltage Alarm	Friday, May 18, 2007 4:40:39 AM
This looks very well, can you pl tel me Zener diode value for +24 V
syaiful	Low Voltage Alarm	Thursday, May 10, 2007 10:04:19 PM
hey!!...i'm totally new about electronics and i have a project on exactly this low voltage alarm but we have to add in sensors..can u actually, kindly advise me what are the things and how to set up the circuit...?..i wud appreciate ur help..Thankz... :)
ahmed algheilania - oman-sur	Low Voltage Alarm	Wednesday, May 09, 2007 5:45:25 PM
can i have the working of this circuit
lui	Low Voltage Alarm	Tuesday, May 08, 2007 10:49:04 AM
Hey I like the circuit. Could you give me details on exactly how this circuit works and any other info regarding it. Also if I wanted to change the voltage being inputted in to around 6V, what necessary changes will I have to make to the circuit and where? Thanks
anonymous	Low Voltage Alarm	Wednesday, April 04, 2007 9:58:04 PM
how to make circuit and discrimsion about syambol use in it
vinay	Low Voltage Alarm	Friday, March 23, 2007 10:21:15 AM
please give me some help how to realize it ..can it realize on a single breadboard..and give how it works..thanx
anonymous	Low Voltage Alarm	Tuesday, March 20, 2007 10:08:13 PM
nice one!!^-^
Emmanuel E	Low Voltage Alarm	Thursday, March 08, 2007 8:03:52 PM
please l will like to ask for your help to enable me or guild me in the production of this low voltage alam,because am writing a project on this.thanks
lou	Low Voltage Alarm	Wednesday, February 28, 2007 4:48:18 PM
Hi , I send you a comment and some qoues. but I didn't realize I can put my e-mail. My Qoue. is again can I use this device to test skin Voltage ? I am still trying to build a Seizure Alert Device in conjuction with voltage measurment of the person skin .
anonymous	Low Voltage Alarm	Wednesday, February 28, 2007 4:15:38 PM
Hey I like this one too ,but can I use it to measure skill voltage of a person? I am still to construct seizure Alert Device by combining different componnets.
Will	Low Voltage Alarm	Wednesday, February 28, 2007 3:58:13 PM
Hello I like your little circuit. I would like to know if it could be mod. so the led would light when a cap reaches a set voltage.