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Breaktru Forum  |  eCigarette Forum  |  Modding  |  Topic: Low Battery Indicator
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Author Topic: Low Battery Indicator  (Read 46329 times)

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Offline jayD

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Re: Low Battery Indicator
« Reply #100 on: September 11, 2014, 11:41:45 PM »
Thanks for the helpful thread, I did build the single battery alert using all the recommended parts, however from 3v-4.2v it's dim and below 3v it's bright. What's needed to make it have no light at all above 3v ? Cheers for any info.

Offline CraigHB

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Re: Low Battery Indicator
« Reply #101 on: September 12, 2014, 04:50:00 PM »
You need to use a comparator or voltage detector chip to provide a digital signal, either on or off.

Offline nwooley83

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Re: Low Battery Indicator
« Reply #102 on: January 23, 2015, 05:30:19 PM »
OK my local supply shop had an NTE999 in stock and the rep said that it should work in place of the 431...

Here is the data sheet on it.

http://www.nteinc.com/specs/900to999/pdf/nte999.pdf

It looks like the specs are pretty much identical but I start to hallucinate looking at data sheets right now as I have been doing so much research on components trying to get our first production mod ready for the shelf.


What do you Wise Ones think?

and any idea on what resistor to change for a 1.86V red led with a 25mA draw?

Offline CraigHB

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Re: Low Battery Indicator
« Reply #103 on: January 23, 2015, 05:39:05 PM »
That's also known as a shunt voltage reference.  It's a common device used for many applications, typically for an ADC reference.  You may be able to use it in place of a Zener diode, but they normally need a bias current full time so that can be a consideration.  When voltage falls off and bias current falls below the minimum, the part can do unpredictable things.  It may not behave the same way a Zener diode does.  You'd have to try it and see if it works.  I can't say if it would do the job or not without testing it in a circuit.

Offline nwooley83

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Re: Low Battery Indicator
« Reply #104 on: January 26, 2015, 08:57:47 PM »
Thanks CraigHB,

  you wouldn't happen to know how much it would change the voltage that the led would come one at if I used a 220 ohm resistor in place of the 240 on the single cell circuit would you?

and the only red LED that I could get at the shop that was close to 2V is the NTE30041 that has a Vf of 1.86 and 25 mA draw which needs a lower resistance.

Update:  Protoboard setup with the 220 resistor (closest i had) and the 1.86Vf LED ... If my multimeter is correct at 3.14 the red led just barely lights up... draining the battery now to see if it gets brighter as it gets closer to 3v

Gah it is lighting up about the same at 3.86 as well... and getting dimmer at 3v

Gonna have to figure out where my breadboard went.... gonna burn something up soldering(probably my fingers) :facepalm:
« Last Edit: January 27, 2015, 08:55:47 AM by nwooley83 »

Offline CraigHB

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Re: Low Battery Indicator
« Reply #105 on: January 27, 2015, 02:50:49 PM »
Shunt references behave similarly to a Zener diode through much of the voltage range, in fact they are often represented as a diode symbol in schematics.  You're finding that current falls off in a parabolic manner as voltage falls off similar to a Zener diode, not surprising, but that's not a normal operating range for a shunt reference.

Like I said before, for an indicator to provide an off or on visual indication you need a digital signal.  Zener diodes and shunt voltage references are analog devices.  You need to use a comparator or voltage detector.

Recently I've come across a device that's pretty simple to wire and has a detection range 400mv to 20V.  Check out the Texas Instruments TPS3700.  I'm actually doing a 2S voltage detector circuit right now using that part, not for an e-cig though.

Offline Zanderist

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Re: Low Battery Indicator
« Reply #106 on: February 05, 2015, 10:11:33 PM »
I found it!
That's what i was looking for...

Do you think this will work???
Could this work with a 2N3904 transistor?

Offline jct

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Re: Low Battery Indicator
« Reply #107 on: April 30, 2015, 01:02:22 PM »
You need to use a comparator or voltage detector chip to provide a digital signal, either on or off.

Or you can try this (Download TPS3809 datasheet from Texas Instruments web site, alternative MAX809 from Maxim; available in various voltages from 2.5 up to 3.5 I think).



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