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Saturday, 16 February 2013

Self Powered 9 Volt Bar LED Battery Tester LM3914 Stripboard Veroboard Layout


another cool little voltage monitor but I had some requirements - I wanted it to be self powered and have an onboard load so I could check any 9 volt battery with it.
this is for a active pickup system so the self powered part of the design wasn't hard to factor in as usable voltage is around 5 ish volts in the EMG's I have.

and Last of all I wanted to use the LM3914 (DATASHEET) cause I've got loads of them from another project I never got around to doing.

I used a 82 ohm resistor (switched in by pressing the push to make switch) this will allow you to test the battery under a normal load which will give you a better indication of the batterys chargethe 82ohm resistor draws almost 110mA

I have done a circuit like this before which was a 0 - 10v voltage monitor (HERE) but the difference between that one and this is that this one is powered by the battery you're testing and the other one though more accurate needs a second power supply.




15 comments:

  1. Hey Paul,
    I messaged you before too regarding 9V Low battery detector. I wanted to know how do we change the threshold voltage means from 6.3V to anything else?I am working on a project so please if u can guide me.It shall be highly appreciated.
    Thanku

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  2. there's another layout that lights up an LED per volt http://www.paulinthelab.com/2012/06/lm3914-voltage-monitor-stripboard.html

    you can't really change the way this works unless it's a higher voltage because it is self powered and needs above 5 volts to run

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  3. Hey,
    thanks for your reply...actually i was talking about one of your other layouts i.e http://www.paulinthelab.com/2012/11/low-battery-indicator-9v-stripboard.html in which the threshold voltage is 6.4V but my circuit is operational at 6V so i want to lower this threshold voltage. If you can guide me with that i shall be thankful

    ReplyDelete
  4. Hey,
    thanks for your reply...actually i was talking about one of your other layouts i.e http://www.paulinthelab.com/2012/11/low-battery-indicator-9v-stripboard.html in which the threshold voltage is 6.4V but my circuit is operational at 6V so i want to lower this threshold voltage. If you can guide me with that i shall be thankful

    ReplyDelete
    Replies
    1. I see, well that one is basically a comparator and oscillator set up and I would have to have a more in depth look at that to change it but it would involve changing R1 and R2 - if you want to have a mess around with it in the meantime

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  5. What a great project you definitely know what you're doing,t he LED monitor is spot on.

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    Replies
    1. cheers dude - it's nice to get a nice comment once in a while.
      this has been quite a useful project in my house

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  6. Hello, I've got some questions about this great project :)
    I was wondering, if I assemble this into my guitar's body... with it suck the power of my battery if I don't push the "load" switch? I mean... is this true bypass? If not, would it be true bypass if I put the switch at "V in"? And at least, where do I have to solder it to be always available for me to push the switch and get the info? It would be a momentary NO switch. Do I have to solder it at the jack terminals?
    Thanks in advance :D

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    Replies
    1. you would remove the load resistor (R5) + the load switch

      attach it to your battery terminals - not the jack terminals. it can't be true bypass because it's not part of the audio signal

      then just have a switch going to the Vin from the battery and then it will use no power when the switch isn't pressed

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    2. Thank you man! I didn't expect an answer this quick! You rules!! If I became famous I will tell about your tester in all the interviews :P I don't think so, but dreaming is free :)
      Anyway, thanks for your answer, and thanks for this great project :)

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  7. hi, a very good project.
    pls clarify what the load switch is for

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  8. I'd love to integrate this into a sag circuit I'm using to drop voltage from a 9V wall wart using a 10k pot. Would I need to change anything? What's the overall voltage drop of the circuit itself?

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    Replies
    1. I actually made a battery simulator with sag that incorporated this in another project http://www.paulinthelab.com/2014/02/battery-simulator-with-voltage-sag-and.html

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  9. Also an interesting circuit, but I'm curious why you had to integrate the IC. My current "circuit" is literally just voltage running through a pot and back out; would there be a way add a 4-5 LED chain for voltage indicators without having to add an IC, caps & resistors? I'm trying to make it under a certain price point and as simply as possible (anything over $4, and I'm better off just buying a cheapo Chinese LED numerical display on eBay). Also, I'm typically working with a max Voltage of 9V, as that's what a majority of guitar pedals run on.

    Either way, thanks for the reply! I'm glad I found your site. It's nice to see someone who's willing to take the time to share and talk about circuits without rolling his eyes at us relative noobs :)

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    Replies
    1. well the problem with the pot method is that if your pedal draws too much current then the pot will burn out.
      all the stuff in the project you can get from chinese grey market eBay sellers for a lot less than $4
      as for caps - you must have broken electronic stuff in your house? I purposefully use values that are commonly used
      in appliances so that people can recycle them - even the 2 diodes that are in it are found in just about everything.

      as for your original question if you use this circuit - you won't get voltage drop because voltage doesn't go through it - it takes a measurement of the voltage rails
      it does draw a bit of current though and you can leave off the load switch and the 82R resistor

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