Low battery indicator(low cost)

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adrian sphank

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Hello, i want to design a simple low battery indicator which using LED and 'buzz' sound like hand phone (warning buzz). Im looking forward at this design.

**broken link removed**

But where is the connection to the circuit?
 
The connection to the battery is the 9V input. It's designed to test a 9V battery.
 
6.9V is also a bit too high for a cut-off voltage, I would have chosen 6V, even 6.2 will probably be all right, just change the zener to 5.6V which is a pretty common value.
 
With the dimensions given both LEDs will light at full battery power.

Here is the modified circuit. The zener used is 5.1V.

UBatt >6.2V = green, UBatt <6.2V >5.5V = green + red, UBatt <5.5V = red, UBatt <4V = no LED

Boncuk
 

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The problem with the circuit above is that they will drain the battery fairly quickly. This is because they draw apx 20ma which means that a regular 9V alkaline will be dead in apx 30 hours even if nothing else is connected.
 
Boncuk said:
With the dimensions given both LEDs will light at full battery power.

Here is the modified circuit. The zener used is 5.1V.

UBatt >6.2V = green, UBatt <6.2V >5.5V = green + red, UBatt <5.5V = red, UBatt <4V = no LED

Boncuk
Click to expand...

How if i want to implement the 'buzz' sound?
 
If you use low current LEDs (2mA) and appropriate current limiting resistors (3K9 instead of 330Ω for 9V) the battery will stay alife longer. Adding a buzzer circuit I suggest to use a dual astable multivibrator (both gated) using a CMOS 4093 and connect a transducer to the output.

With the gated osicillator you'll have an intermittant tone signal which is more alarming than a steady signal. Additionally it uses less battery power.

Boncuk
 
kchriste said:
Not quite. Referencing Boncuk's diagram; connect the buzzer between the collector of Q2 and +9V. Or, to put it another way, in parallel with the D3/R5 network.
Click to expand...

Thanks!!!Understanding confirm!!!!!!

Additional question : How i want to have 'warning' sound like nokia Hp?
 
Last edited:
If you need a pulsed tone, you can get piezo buzzers that give a pulsed tone.

If you want anything more complicated than that, then you're outside the realm of simple and cheap.
 
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