Circuit protections for Alkaline AAA

Thread Starter

kiltro

Joined Oct 24, 2011
10
Hello everyone,

I've designed a simple circuit with a PIC16F59 that drive an RGB led and a small buzzer, the circuit is powered by 2 AAA batteries.

Do you suggest any protection circuitry like low-battery cut-off and overload.
Is there any easy circuit that can easily perform the above protections? (I've limited space for the components, already using smd)

Thanks
 

Audioguru

Joined Dec 20, 2007
11,251
What do you want to protect? When the alkaline battery dies then it is dead and there is nothing to protect.
I hope you are not thinking about trying to charge the non-rechargeable battery.
 

dl324

Joined Mar 30, 2015
8,885
Welcome to AAC!

It's always helpful to post a schematic or block diagram of the circuit you're talking about so we can better understand what you're asking for.

Are you trying to implement a low voltage cut off to prevent erratic operation of the microcontroller? Is there potential for adding additional "stuff" that could cause excessive current draw from the battery?
 

Audioguru

Joined Dec 20, 2007
11,251
Maybe protection is needed from preventing an idiot from connecting the battery cells backwards?
 

crutschow

Joined Mar 14, 2008
23,318
Do you suggest any protection circuitry like low-battery cut-off and overload.
Low-battery cut-off is only needed if you have to shut down the circuit before its operation could become erratic from the low voltage.

What would be a possible cause of an overload?
 

GopherT

Joined Nov 23, 2012
7,983
Do you suggest any protection circuitry like low-battery cut-off and overload.
No, based on mine and everyone else's opinion, we don't suggest you add any cut-off or overload protection circuitry for an alkaline AAA powered circuit.
 

Thread Starter

kiltro

Joined Oct 24, 2011
10
Thanks everyone for answering.
Here is the schematic.

My questions start from the fact that the batteries and pcb will be housed in a very small metallic enclosure connected to negative (basically a cylinder with internal diameter almost equal to that of the batteries) so my thought of overload protection is more a short-circuit protection (only one I can think of is between the spring touching the + and the enclosure).

Low batteries protection was to avoid led lights while buzzer doesn't beep anymore (due to low voltage of the batteries).

Another question, in the buzzer datasheet here, I see a max mean current of 110mA. How can I determine the min current instead? What the minimum current to get sound?

Please forgive my bad english!
 

Thread Starter

kiltro

Joined Oct 24, 2011
10
I realized now the schematic is missing a diode in parallel with the buzzer...
 

AlbertHall

Joined Jun 4, 2014
8,337
What kind of buzzer is it?
1. Piezo - Apply DC voltage and it buzzes.
2. Piezo - Apply ≈3kHz voltage and it buzzes.
3. Electro-mchanical - apply DC voltage and it buzzes.

1. Will work fine in your circuit and no diode needed.
2. This won't work in your circuit. You will need to add a resistor across the buzzer to allow a DC path for the transistor collector current. No diode needed.
3. This type may need a diode and will work fine in your circuit.
 

Thread Starter

kiltro

Joined Oct 24, 2011
10
There is an error in my original post, it's a PIC12F509
There is a brown-out circuit in the datasheet but it uses the MCLR pin that in my case is set as an input.
 
Last edited:

Thread Starter

kiltro

Joined Oct 24, 2011
10
What kind of buzzer is it?
1. Piezo - Apply DC voltage and it buzzes.
2. Piezo - Apply ≈3kHz voltage and it buzzes.
3. Electro-mchanical - apply DC voltage and it buzzes.

1. Will work fine in your circuit and no diode needed.
2. This won't work in your circuit. You will need to add a resistor across the buzzer to allow a DC path for the transistor collector current. No diode needed.
3. This type may need a diode and will work fine in your circuit.
I'm not sure about your question... it's the one in the datasheet I've posted
For what I understand you have to apply a 4kHz square wave to the base of the npn (so maybe the 2nd in your list?)
 
Last edited:

Audioguru

Joined Dec 20, 2007
11,251
Why are you using an old fashioned high current magnetic mechanical transducer (speaker) instead of a modern low current piezo beeper that has its own oscillator inside?
 

GopherT

Joined Nov 23, 2012
7,983
His circuit shows a 8 pin chip is why I ask.
View attachment 143965
I don't like to use the MCLR as a reset, I would rather use an ADC and sleep if below a threshold voltage. The MCLR is like a self-destruct button and you never know when it will pop). With the ADC, a planned shutdown (sleep) can be executed.

Note, external voltage reference (zener) can be toggled with a second GPIO (Output high to activate, then set to input when not needed).
 

GopherT

Joined Nov 23, 2012
7,983
You should add current limiting resistors to GP1 and GP2.

You need a pull-up resistor on GP3.

If your speaker is a standard speaker, you might fry it with DC current. Speakers should be capacitively coupled to your supply.
 
Top