SparkFun Forums

[Loobieburt]

Any easy quick suggestions for a low battery alert flashing led for a pp3?

[lyndon]

What's a pp3?

[Ross Robotics]

Maybe http://en.wikipedia.org/wiki/PP3

[Mee_n_Mac]

http://en.wikipedia.org/wiki/Nine-volt_battery


Either that or the 3'rd invasion wave of the Pod People

[lyndon]

Probably.

I've learned not to expend too much trouble figuring out people's posts. There's a strong correlation between not being able to explain what you want and not being too interested in a solution aka not showing up to read the responses ...

Or maybe I'm just in a crabby mood

[Loobieburt]

Sorry should have put on more.
It's a pp3 9v doc battery.

I have a basic alarm that works via pp3 and would like to add an indicator to show me why the battery is getting low?

Possible a flashing led to indicate it is below 6v

Any ideas or tips?

Many thanks

[Loobieburt]

Should have said 9v doc battery as per the image above

[lyndon]

Is that a typo? Do you mean "why" or "when?"

Don't know how to do "why" but a very simple battery low indicator is a comparator and a high efficiency LED. Problem is that the LED will drain the battery faster. So your thought of flashing is good: less power being used.
Here is an example of an LED flasher circuit using the ever-popular LM555. Now, if we modify the circuit so that pin 4 (RESET) is held low when the battery voltage is high enough, then flashing will start when the battery voltage is above that setpoint. The "problem" is that this adds more components, and complexity.

I'd do it with a small microcontroller. Just need to measure the voltage with the onboard ADC and flash the LED if it's below a threshold. Only needs a single chip and an LED.

OTOH, for an indoor application where you aren't away from the alarm for a very long time, a very high efficiency LED may be bright enough with just 1 mA operating current so the comparator circuit may be just fine.

Sorry should have put on more.
It's a pp3 9v doc battery.

I have a basic alarm that works via pp3 and would like to add an indicator to show me why the battery is getting low?

Possible a flashing led to indicate it is below 6v

Any ideas or tips?

Many thanks

[Loobieburt]

Thank you. I will have a go

[lyndon]

I should add that since adafruit came out with the Trinket, that would be a great way to prototype this. the entire device could be glued to the battery!