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Low battery indicator(low cost)

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crutschow

Well-Known Member
Most Helpful Member
The connection to the battery is the 9V input. It's designed to test a 9V battery.
 

Hero999

Banned
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.
 

Boncuk

New Member
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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kchriste

New Member
Forum Supporter
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.
 

adrian sphank

New Member
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

How if i want to implement the 'buzz' sound?:D
 

Boncuk

New Member
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
 

Hero999

Banned

kchriste

New Member
Forum Supporter
Add the buzzer parallel with RED LED right?
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.
 

adrian sphank

New Member
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.

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

Additional question : How i want to have 'warning' sound like nokia Hp?
 
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kchriste

New Member
Forum Supporter
I have no idea what a "nokia Hp" sounds like. Maybe someone else does.
 

Hero999

Banned
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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