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555 timer buzzer circuit not working...

Proschuno

Aug 1, 2011
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So I've connected an NE555 timer to an LM386 amplifier, attempting to maybe perhaps get a 'squarewave' buzz... I'm using about 5.5 volts from a battery pack, and made sure all the connections are working. Hooking it up to a small 8 ohm speaker, nothing's coming out.

I'm thinking it's probably the gain; I don't think i have the right size capacitor, and i've tried googling equations for the amplifier gain to connect the capacitor and resistor (even just throwing a single capacitor and putting the gain to 200 doesn't do much).

This is my first time actually doing and electronics project, so basically I have no idea what i'm doing..... well, some idea, but yeah lol.....
 

Harald Kapp

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Can you post the schematic? Without it is rather impossible to judge what might have gone wrong.

Harald
 

Proschuno

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Alright, here's the schematic; pin 3 on lm386 is non inverting input, while 2 is Inverting input. Also, forgot to mention they get rather hot when i flip the switch

Also, forgot another huge thing, silly me. Last night I tried doing it, i accidentally connected the power (VCC if you will....) to pin 3 on the NE555, so another explanation is that i think i fried it...... and probably the amp to i'm sure.
 

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Harald Kapp

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The LM386 needs an output capacitor for decoupling the speaker. See http://www.ti.com/lit/ds/symlink/lm386.pdf page 6. Probably there is a DC component at the LM386's output. On an 8 Ohm speaker this DC component will draw too much power from the LM386, possibly destroying both IC and speaker. By adding a series capacitor you can block the DC component.

Your 555 oscillates way too slow. At ~0.05 Hz this is well below the audible spectrum. For a buzzer 50 Hz - 100 Hz would be much better suited. See http://freespace.virgin.net/matt.waite/resource/handy/pinouts/555/index.htm for a tool to calculate the 555.

Harald
 
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Proschuno

Aug 1, 2011
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Thanks a Million... I actually realized i calculated the frequency wrong any way. I'll try it that way and see what happens
 

Proschuno

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Well sadly, I tried new IC's and placing capacitor before the speaker to take out dc component and such... no luck. similar parameters as before, except I've placed several capacitors in parallel before the speaker to filter out the dc component, and several capacitors between output and ground. (values aren't known, but i figured this is just to filter out dc components and such.... it's not super important i assume.)
 

(*steve*)

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No, the capacitor goes in series with the output.

output -- one end of capacitor,
other end of capacitor to one end of speaker,
other end of speaker to ground

Use something between 10uF and 100uF

And have you sped up the 555? The resistor values you're using are greater than the maximum recommended in any case and it may not even be oscillating. Even if it were, you might expect to hear a click about once every couple of minutes.

Have you looked at the datasheet for the amplifier to see how they recommend you use it?
 

Proschuno

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I know, i put several capacitors in parallel together... in series with the out put

Actually, i just got the thing to work; i was connecting pin 4 to ground, while it's supposed to be connected to 8. I've also adjusted the resistor values. So it buzzes away to its heart's content....
 

twister

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You need to hook a 0.1 cap. to ground on pin 5, on the 555. Pin 5 is the control. It will lower the frequency the closer it is to ground. You could put a pot there, or a transistor, if you want to vary the freq.
 

Proschuno

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Thanks twister, i didn't realize that.... now having even more fun. :D
 
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