[Beginner question] Fitting a low-voltage alarm into this circuit.

Karolina's picture

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Joined: Apr 16, 2019

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[Beginner question] Fitting a low-voltage alarm into this circuit.
April 16, 2019 - 3:01pm

Hello,

I know very little about circuits and electrical components, so please be kind.
Attached is a picture of a simple circuit. "A" is a 4,5V AAA alkaline pack, "B" is a latching pushbutton switch and "C" is a nicrome wire.

In the simplest and cheapest way possible, this circuit needs to alert the user if the battery pack goes below 3V. The indication signal needs to be a "beep", just like a smoke detector. (I can't have a LED signal).

After some googling, I found that a 3V "low signal relay" incorporating an alarm/buzzer could be one option. I prefer to use wires, and not a PCB in my circuit.

My questions follow below:

1. Is a low signal relay this the cheapest and simplest way, or are there others?
2. Do these relays come with a beep sound?
3. When in standby-mode, this relay should not draw power from the alkaline pack, therefore it needs to be powered from an external (coin cell?) battery.

Is there such a product that I can buy off-shelf and where in my curcuit do I fit it?

All help highly appreciated.
Thanks!
/Karolina

 

circuit.jpg

AISHA's picture

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Joined: Sep 07, 2017

Replies: 249
Lets answer the quesions one
April 19, 2019 - 12:05pm

Lets answer the quesions one by one.

1. Is a low signal relay this the cheapest and simplest way, or are there others?

A strict NO, A low signal Relay is not meant for this application. The relay will turn on arround 3V, for a 4.5V battery it will remain turned on till the voltage reaches 3V (not very preceises here) or less and then the relay will turn off triggering the buzzer. When the relay is turned on it will draw some current from the battery for sure. So no, this is not the cheapest or effecient way to be followed.

 

2. Do these relays come with a beep sound?

No they dont, but you can easily interface a buzzer to its output pins.

 

3. When in standby-mode, this relay should not draw power from the alkaline pack, therefore it needs to be powered from an external (coin cell?) battery.

And how often will you be replacing that coin cell? As I told earlier the relay will be consuming some power so it is not a good idea to use a relay if you are concerned on saving the juice in your battery.

Is there such a product that I can buy off-shelf and where in my curcuit do I fit it?

There are many, which you can buy and make minor alternation to fint in your project. But I cannot suggest any since I do not know vendors in Norway.

 

Best way to built it:

The ideal way is to use an Op-Amp as comparator. It might sound all complicated for a beginner, but it is realy easy. You can also read through the below article to get an idea of how it would work 

https://circuitdigest.com/electronic-circuits/battery-monitor-circuit

 

This way the low battery indicator circuit will draw very current allowing the battery to last longer