Continue to Site

Welcome to

Welcome to our site! is an international Electronics Discussion Forum focused on EDA software, circuits, schematics, books, theory, papers, asic, pld, 8051, DSP, Network, RF, Analog Design, PCB, Service Manuals... and a whole lot more! To participate you need to register. Registration is free. Click here to register now.

Low voltage buzzer alarm

Not open for further replies.


Member level 1
Nov 25, 2019
Reaction score
Trophy points
Activity points
Hello. I am building low battery buzzer alarm. I have done this guided by schematics and it works great. My question is is it reliable to leave it just like this in boat with few components? I see in the datasheet of lm339 that it can hande much bigger voltage then 12V (around 30) so I would put maybe just 18V TVS between + and - and one amp fuse... Do you think that is ok or someone have some good advice to make it more reliable?


  • batt.jpg
    31.6 KB · Views: 148


The circuit does what it ought to do.

But I personally don't like these circuits. Why? Because they are on a boat ...but you are not there. So if the battery voltage drops, it switches ON the buzzer and the LED, drawing even more current from the battery. The voltage faster drops below the "healthy" line ..
No timeout, no undervoltage protection. Other people around - maybe in the night - get stressed by the noise.
And maybe the battery lifetime is less than without this circuit.

Maybe it has an extra switch ... to switch it OFF when you leave the boat. But since the circuit usually is quiet, it is likely to be forgotten.

I don't know how/when you use it ....

So my solution is an "early" alarm. Maybe a minute or five (maybe with alarm_reset_button) before the battery leaves the healthy voltage range.
But then it shuts down. It shuts OFF the alarm, the LED as well as all other loads... to keep the battery as long alive as possible.

... my opinion...


Great idea. I will put a switch to it so that it can be turned off when leaving the boat. The boat is for rental purposes, so alarm is for guests actually when they are abusing the batteries...

Not open for further replies.

Part and Inventory Search

Welcome to