LM386

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unknown_entity
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LM386

Post by unknown_entity » Wed Apr 16, 2003 10:53 pm

ok im looking at the pinout of this chip, can't make sense of it. I have never used op amps before so i not sure what goes to what.<p>8 Pin DIP
---------------------
.....Gain**1--o--8**Gain
..-Imput**2-----7**Bypass
.+Imput**3-----6**Vs
.....Gnd**4-----5**Vout<p>Better yet i tell ya what i want to do. i want to take the output of a 555 in the audio range(nothing really too low or hi) and use the 386 to drive a small 8ohm speaker or maybe a piezo.<p>I have no idea what gain and bypass do.<p>Correct me if im wrong:
*Vs and Gnd are power supply pins for the chip<p>*Vout is the amp's output (a zero or positive voltage? but never dropping below Gnd?)<p>*Then is Vout is a +voltage then i would sink
it to Gnd thru the speaker<p>*I'm guessing a pot in line with the gain will change the...well the gain of the amplifier.(but why is there 2 pins labeled gain? For cascading amps?)<p>anyone care to explain this or at least post a url.<p>Oh, one more thing is there any other chips that i could use in this applicaion because when powered by only 6V driving an 8ohm speaker the THD is already at 10% are all 386's this crappy or is it just the junky radio shack ones i have?<p>Or maybe thats the maximum tolerences one says 10% the other .2% i don't know.<p>[ April 16, 2003: Message edited by: unknown_entity ]</p>

hamsterears
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Re: LM386

Post by hamsterears » Wed Apr 16, 2003 11:15 pm

http://www.warplink.com/user/kencan/lm386.htm<p>The 386 is a very good chip, I've used them several times.<p>The "Gain" control between pins 1 and 8 changes the gain from 20-1 to 200-1 by adding a capacitor, as shown in the link listed above.<p>Vout is the output.<p>Pin 2 is the inverting input, and pin 3 is the non-inverting input. This means that the inverting input will invert the input, ie, if it's +3v, it'll come out -3v, and vice-versa. By using the pot you can control the volume. (There are other ways to set this up, BTW)<p>Vs and Ground are the power supply.<p>Hope this helps.<p>Michael Fagan

russlk
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Re: LM386

Post by russlk » Thu Apr 17, 2003 1:30 pm

The 555 can output 200 mA, so it could drive the speaker thru a capacitor (like the LM386). Don't use the CMOS version, it doesn't have the drive.

EARTHSTAMP
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Re: LM386

Post by EARTHSTAMP » Thu Apr 17, 2003 6:10 pm


unknown_entity
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Re: LM386

Post by unknown_entity » Thu Apr 17, 2003 7:04 pm

i might be able to get aroung using an amp cause i was messing around with some breadboard stuff today and it worked pretty good without one

Donald S. Lambert
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Re: LM386

Post by Donald S. Lambert » Fri Apr 18, 2003 2:23 pm

I don't know your electronic expertise but Radio Shack has (or had if no long available) a book titled "Getting started in Electronics' by Forrest M. Mims, III that has information on op amps plus a lot of other solid state chips. There are other books that Radio Shack has that might be worthwhile for youi to take a sneak look at to decide if they are what you want to learn about.
HTH Greybie.

gadgeteer
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Re: LM386

Post by gadgeteer » Sat Apr 19, 2003 12:26 am

My phone line is fried, always has been. Two different CALL-WAITING-DETECTORS did not detect (had to buy 8 answering machines before I found one that could be accessed remotely). <p>The "I-Ring" uses a PIC, but also uses an LM567 searching for the single CALL-WAITING "beep"; I interrupted the OC output of the 567, and fed it to a 386 (minimum gain). Volume control protrudes through the case, and I can adjust the volume so that it works every time. (A tiny piezo buzzer across V+ and 567 OUT continuously announces the health of the signal).<p>As delivered, the I-Ring would detect about 3% of the calls while internet-surfing (at the MOST! But ALL the detectors and answering machines work perfectly ANYWHERE ELSE IN TOWN!); detection is now 100%.<p>386 works fine on a single 5V supply, with no input biase problems (most op-amps require the exact same biase voltageon both inputs, and same resistance-to-ground before they will function). Very easy, very functional...<p>[ April 19, 2003: Message edited by: gadgeteer ]</p>

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