USB powered speaker circuit doesn't work

ian field

Joined Oct 27, 2012
6,539
Heat shrink tubing! If you don't have an electronics store nearby, Harbor Freight carries a selection as does marine supply stores.
You can also get the sleeving coated with heat activated adhesive on the inside - but I don't know about from the suppliers you mentioned.

You can also get complex shapes "trouser" sleeves with a large diameter at one end and 2 or 3 smaller sleeves emerging at the other end - handy for sealing the end of the outer covering on cables with 2 or 3 insulated conductors.
 

Thread Starter

tjohnson

Joined Dec 23, 2014
611
When I made my speaker, I soldered three 28-gauge wires each about a foot long to a headphones plug, since I didn't have an entire stereo audio cable but just a right angle plug from the end of one. The wire left on the plug was very short because some of it had broken off. Now one of them broke again, and there really isn't any metal left to solder to.:(

I bought an audio cable with bare wire ends on eBay, but didn't realize until after it had been shipped that it was mono, so it won't work.:mad: (My speaker is mono, but my computer's audio socket is stereo so I need to use a stereo cable.) So I'll probably resell it on eBay.

I didn't know until I researched some more that there are metal headphones plugs available for only ~$2.:) The only disadvantage of these is that they wouldn't lengthen my wires or keep them from getting tangled.

Yesterday I had the thought to stop at the Dollar Tree in town (where everything's $1) since I thought they might have some earphones, and they did so I bought a pair. The speakers on them are probably poor quality, but my idea was to cut them off and throw them away and just use the cord.:p

This idea sort of worked. I soldered the new wires on last night, but when I tested my speaker there was definitely a bad connection somewhere. When I tried to find it, the audio completely stopped, so it looks like I have some more work ahead of me.;)
 
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Thread Starter

tjohnson

Joined Dec 23, 2014
611
I think the problem is that the audio wires are still coated with lacquer. How can I strip this coating off? Can I burn it off with my soldering iron, or sand it off with fine grit sandpaper?
 

ScottWang

Joined Aug 23, 2012
7,080
I think the problem is that the audio wires are still coated with lacquer. How can I strip this coating off? Can I burn it off with my soldering iron, or sand it off with fine grit sandpaper?
Scrape it with a knife, and soldering the wire with Tin and the Tin should be encase the wire through whole section of the wire where was scraped, when you soldering the Tin and wire will be as these:
Θ------
-Θ-----
--Θ----
---Θ---
----Θ--
-----Θ-
------Θ
------- Θ
 

Thread Starter

tjohnson

Joined Dec 23, 2014
611
Can anyone give an estimate of how much current this circuit would draw from a 5V USB power supply?


I got a portable USB charger with a capacity of 2600mAh and would like to have an idea of how long it can power my speaker. I tried measuring the current with my multimeter, but it didn't work (probably because the battery is running low, which is a non-standard size that's difficult to find a replacement for).

My circuit is similar to this one, which according to the article draws only 4mA. If I used that number to estimate how long the USB charger would last, it would be 2600mAh/4mA = 650 hrs! Does that seem like a reasonable estimate?
 
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Thread Starter

tjohnson

Joined Dec 23, 2014
611
My circuit is similar to this one, which according to the article draws only 4mA. If I used that number to estimate how long the USB charger would last, it would be 2600mAh/4mA = 650 hrs! Does that seem like a reasonable estimate?
I see now that this estimate is too high, since according to the LM386 datasheet, the low quiescent current drain is 4-8mA. That tells me how much current the IC draws when it's inactive, which is only somewhat helpful. I know that the amount of current drawn when it's active could vary considerably, but I'm surprised that I haven't been able to find an approximate range.
 
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