LM386 Amplifier Chip

Discussion in 'The Projects Forum' started by vrinsk, Mar 30, 2014.

  1. vrinsk

    Thread Starter New Member

    Mar 30, 2014
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    Hi all, I've lurked this forum a few times but this is my first time posting. I bought this amplifier chip on ebay. I wanted to try to make my own portable speakers with rechargeable battery but I can't get it to work so I was hoping someone with experience could help me out.

    Here are the materials I'm working with:

    The LM386 chip I bought on ebay
    A mini-usb chip I bought on ebay
    An 8 ohm 3 watt full range speaker (I have 2 but I was testing with 1)
    Old cell phone with music
    An old cellphone battery

    The box where I put everything is where I hope to put the speakers and the components. I haven't been able to figure out what the third terminal on the battery is, there's a positive symbol on one side and a negative on the other and nothing on the middle so I'm not sure how to connect it so I've been testing the amplifier chip with a 9V battery.

    The dupont cables are connected as follows:

    Black= ground
    White= ground
    Gray= in
    Purple= VCC

    I had connected the black and red from the input cable to the gray In and the ground to the white ground, then the black ground. The out of the chip I connected the positive cable of the speaker and the negative to the Ground of the chip.

    I had connected the positive of the battery to the VCC and the negative to the Black Ground, then I think I switched the black ground for the white ground and um yeah, I made sure the speaker works with another chip I have from a unit I had dismantled so I'm pretty sure the speaker works and I'm not sure how to put it all together and make it work, it's been a frustrating 2 weeks while I've gathers all the parts and been tinkering here and there.

    I'm pretty new at electronics but I've been reading and experimenting with DIY kits, this is my first time I try something without instructions and spare parts. Any help is appreciated. Thank you.
     
  2. elec_mech

    Senior Member

    Nov 12, 2008
    1,513
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    Welcome to AAC.

    The cellphone battery you are using will not work. These are typically rated around 3.6VDC and the LM386 circuit you purchased needs a minimum of 5VDC to operate. You could look for a buck/step-up voltage converter that would boost the 3.6V to 5VDC or more. Something like this should work.

    This should work with the 9VDC battery. Does it?

    The LM386 will only amplify one channel. Most players will output stereo (two separate channels). I've attached a wiring diagram showing you how to connect two speakers with two amplifier modules to get stereo sound. If you only have one amplifier, you can just hook up one with one speaker.
     
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  3. vrinsk

    Thread Starter New Member

    Mar 30, 2014
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    I didn't try it with the cellphone battery, I'm using a 9V battery for testing. Yeah I'm testing it with just 1 speaker since it's not dual channel, I thought testing with a 1 channel amplifier would do for now if I can get it to work :/ I need to familiarize myself more with these circuit parts and schematics, it's confusing sometimes.
     
  4. vrinsk

    Thread Starter New Member

    Mar 30, 2014
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    I bought the DC booster as suggested and have no idea how to put it all together. Haha. I was hoping if someone could put me in the right direction. I'm not sure how to connect the battery to the charger and the DC booster.
     
  5. wayneh

    Expert

    Sep 9, 2010
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    One way to proceed is to divide and conquer. I mean, make your amplifier and speaker work first with a 9V battery, then work on powering it, then the next task, and so on. Don't fumble in the dark. Get a cheap meter (they're often free at Harbor Freight, only ~$5 if you don't have a coupon) and use it.
     
  6. Experimentonomen

    Member

    Feb 16, 2011
    331
    46
    Thats the worst advice ever!!!

    Cheap meters are ****!!! You get what you pay for. Good reliable multimeters start at 100 dollars, with luck you might get a good one for 50 dollars, but no lower than that.

    Below 50 dollars its all the same cheap crap as the 5 dollar ones.

    This is the one reason why beginners cant get their stuff to work, they get tricked by their cheap meter.

    Also the LM386 is about the worst amp ic that you can pay money for. A much better choice would have been one of those little class d amp modules you can get on ebay for 15-20 dollars, those will blow the LM386 clear outta the water in every aspect, some even accept the 3.7V liion/lipol cell directly.
     
  7. vrinsk

    Thread Starter New Member

    Mar 30, 2014
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    I already got the speaker working with a 9V battery and bench power supply now I just want to make it mobile. I know the LM386 isn't the best but if I damage it I won't really miss it, I just wanted to experiment with cheap components first since I'm just learning in my free time.
     
  8. tracecom

    AAC Fanatic!

    Apr 16, 2010
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  9. wayneh

    Expert

    Sep 9, 2010
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    That's an extraordinary claim, requiring extraordinary data to back it up. Got any?
     
  10. elec_mech

    Senior Member

    Nov 12, 2008
    1,513
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    See picture below. Note that you cannot use the USB battery charger for the cellphone battery. That charger is simply designed to work in place of a wall charger - the battery would have to be installed in the cellphone and charged as normal with a USB cable. The circuitry in the cellphone is what handles the battery charging.

    If you really want to charge the battery, I can do some looking for a pre-built module on eBay if you'd like. I know there is a MAXIM IC that can do this, so I'd suppose there is a cheap module out there.

    +1

    I can see Experimentonomen's concern as I got a couple of the cheap Harbor Freight meters and one doesn't work insomuch I can't get a good contact between the probes and meter despite opening them up a bit. But this can be checked at or simply returned to the store. I've been using a cheap $20 for almost a decade without issue (unless I leave it on and the batteries die since there is no auto shutoff feature). A good (but pricey) meter is fantastic, but I wouldn't rule out cheapies altogether, especially if you're starting out or don't have a large budget.
     
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  11. Experimentonomen

    Member

    Feb 16, 2011
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    Just watch EEVblog, he urges beginners to not skimp on a DMM.

    Cheap meters are not trustworthy, i've seen ones that have shown completely random numbers that had no relevance to what was beeing measured.
     
  12. wayneh

    Expert

    Sep 9, 2010
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    Fair enough. I guess I've been lucky - I've got maybe a half dozen of the free HF meters and I've never had a reason to question one of them.

    Either way, the advice stands: Measure things, again and again. If the measurement isn't what you expect - and you should understand what you're doing well enough to make a prediction - then you've just learned something important. You have a chance. With a complex system and no tools, you have almost no chance.
     
  13. tracecom

    AAC Fanatic!

    Apr 16, 2010
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    One thing about Dave: he may not always be right, but he's always certain and loud. Just for the record, I have a Fluke 115 and a $30 Harbor Freight meter. They are usually in perfect agreement...except the Fluke doesn't have a thermocouple input, so I can't verify the one on the HF.
     
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  14. THE_RB

    AAC Fanatic!

    Feb 11, 2008
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    Cheap meters are generally pretty good. I'm not sure about the free giveaway ones, but meters in the $20-$40 range are usually good.

    In the workshop we used cheap meters for the apprentices who had a tendency to wreck them. The cheap meters read quite accurately compared to the good Fluke meters.
     
  15. AnalogKid

    Distinguished Member

    Aug 1, 2013
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    I think some people confuse something that doesn't work (sample defect) with something that can't work (design flaw).

    I now three of the HF wonders, one coupon freebie and two identical meters that were promotional giveaways - from mil power supply companies. All work so well that I usually travel with one of them instead of one of my Fluke 7x's. Smaller, lighter, etc. and I don't care if one gets trashed or forgotten. Plus, I've given away two as good will gestures. Cheap PR.

    And I agree with the above comment about knowing what you're measuring. Think, then measure. If the result is a little off, that's a clue, probably about the circuit. If it is way off, that is a different clue, maybe about the test set. To respin an old truth, Think twice, measure once.

    ak
     
  16. wayneh

    Expert

    Sep 9, 2010
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    Haha, that's optimism. At my age, I think and draw ten times, measure 3, cut twice, sand and fill, go buy more wood. :p Ok, it's not usually that bad. Just sayin'.
     
  17. ErnieM

    AAC Fanatic!

    Apr 24, 2011
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    One meaurement tells you very little.

    In times of uncertainty measure it again using a different meter or different technique.

    Measure things you think are good to insure in fact they are good.

    I have a few HF meters and while I wouldn't swear by them I have never sworn at them. A cheapie meter is better then licking your fingers to find where the AC comes out.

    In summation, as my favorite President stated many many times:

    Trust, but verify.
     
    Last edited: May 21, 2014
  18. wayneh

    Expert

    Sep 9, 2010
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    So true. I worked for years in R&D and take for granted that you have to run controls with any experiment, and every measurement is an "experiment". It's unthinkable that you would use any instrument without checking its result on a known sample. I don't care how much you paid for the meter. ;)
     
  19. BobTPH

    Active Member

    Jun 5, 2013
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    Indeed. I have some counter-evidence. I have been building electronics and made many circuits work over 45 years without paying $50 or more for a meter.

    Bob
     
  20. vrinsk

    Thread Starter New Member

    Mar 30, 2014
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    0
    Thanks for the free lesson on multimeters guys :) I've been using whatever I have at hand at the moment since I cannot afford much. I'll have to think of something else to make this battery work. I managed to build an LM386 amp circuit with audio pot so now I have 2 amps which means I can make it stereo now, just have to figure out how to power both amps with a rechargeable battery that can be charged via USB (cause that's my goal for this experiment as a total no0b in electronics).
     
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