Low battery indicator(low cost)

[adrian sphank]

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?

 

[crutschow]

The connection to the battery is the 9V input. It's designed to test a 9V battery.

 

[Hero999]

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]

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

 

[kchriste]

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]

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?

 

[Boncuk]

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]

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.

I agree, increase R3 and R5 to 680R or even 1k.

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

Add a piezo buzzer.
piezo buzzer - Google Search

 

[adrian sphank]

Add a piezo buzzer.

Add the buzzer parallel with RED LED right?

 

[kchriste]

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]

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?

 

[kchriste]

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

 

[Hero999]

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.

 

[adrian sphank]

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.

nop,i just want cheap n simple.