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Help fitting a low voltage indicator into this circuit? Answered


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 9V fire detector. (I can't have a LED signal).

After some googling, I found that a 3V "low signal relay" 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. What components do I need to achive the "beep" and where in the circuit do these components go?
3. Will these components draw any power in standby mode, or do they only consume some power when the "beep" goes off? Because if they draw power continuously, I will need to add an extra (coin cell?) battery, as I need to save my alkaline pack for the nichrome wire. The extra battery shoud last for min 3 years.

All help highly appreciated.


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Reply 1 year ago

Thanks Alex! I’ll reply you on email as soon as I find the time. Awesome.


1 year ago

You will need an ultra low drain op-amp a coin cell (good for 3y) and a 2 pin crystal beeper and four resistors..

I have successfully designed a battery whistle detector op-amp circuit that responds with a beep at 30 feet in a forest summer-winter-summer for my daughter's geocache..
I will try to find the schematic if you like..

There still will be a fractional micro-amp current draw from your 4.5V AAA alkaline pack because the necessity to compare the voltage..
You do understand that when the AAA does read below 3V it will deliver much less when the button is pushed !

A good idea would be to place as big a capacitor as your device permits across 4.5v AAA Batteries, because the capacitor will charge at once and there after present no added load, it also has No internal resistance compared to the AAA batteries.. The capacitor can supply heavy current when the Nichrome wire initially low resistance pulls a heavy current, then as the nichrome heats up its resistance increases and the battery can continue to heat the wire..
This all occurs in 100 milliseconds..

The contacts on your switch should be iridium (spark plug) or gold plated, not silver.