Audio alarm timer, tantalum value issue help

[plutes]

Hello again, I was following a book and have become stuck what is best to do. The book recommends a 33uf tantalum 10v capacitor but I have a 33uf 16volt. Actually they are only tantalums I own. Ive tested with a multimeter and it climbs to around 8volts dc and then steadily start dropping.

Ive tried reducing the r3 to 100k and that speeds up but doesn't discharge the capacitor.

My issue is I only have two lm380n, so am a bit scared about damaging the ic if I was to test the circuit with a electrolytic, will this damage it?

 

[Nanren888]

Not quite sure what you want to know.

>>The book recommends a 33uf tantalum 10v capacitor but I have a 33uf 16volt. Actually they are only tantalums I own. Ive tested with a multimeter and it climbs to around 8volts dc and then steadily start dropping.

Where does the electrolytic come in?
Were you wanting to swap C2 for an electrolytic?
Was the drop in R3 related to the comment about leackage current in the text?
Yes, likely the leakage for elcrtro might be greater than for tantulums.
.
Is it a typo in
... this is insufficient to overcome the forward threshold voltage of Dl....
Should this be D2?
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The LM380 is just an oscillator, enabled and disable by the output of IC1. If it oscillates happily when D2 is out, then I think you are safe playing with the input stage of IC1, regarding any possible damage to the LM380.
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The main explanation for the workings of IC1 is in project 11, the one before this one.

.

 

[plutes]

use a electrolytic for the tantalum. I didn't make the project before attached, being its just lights a led. But saying that this part of the circuit works, the led comes on after a set period of time. The loudspeaker fails to make any audio tone. Yes I did have the loudspeaker attached when I tested it.

I don't know if its a typo. Its a beginners breadboard book, I don't know what forward threshold even means, if its only the ic1 could possibly get damaged worth a attempt with a electrolytic cap of 10volt

 

[plutes]

pin 14 found it

 

[Nanren888]

The circuit runs on 9 volts. So the 10 volt capacitor is fine from a voltage point of view.
Electrolytics might have greater leakage current, so the timing may change, or if great, might never time out. If you see the LED change, the timer is working.
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If no sound, check the second half. According to the description should sound if you lift D2 as D2 is supposed to keep it turned off till the timer finishes.
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A simple model for a diode is that they start conducting when the voltage across them reaches a threshold the forward voltage drop. About 0.6, 0.7 volts for Si diodes, common now. So commonly used to make things only happen after/when the voltage at a point is higher than some finite number of volts.
Here the output of the IC1 stage won't go right down to groud, zero volts, when off, so the diode allows the output to be anything less than 0,6 volts and the timer will appear to not stop the oscillator working.
I didn't check your protoboard layout. If its not oscillating. check the second stage.
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Unless I missed something. Always possible.

Book available as a pdf online it seems. I searched a sentence from the text you showed.

 

[plutes]

Yes was the 2nd half pin 14 wasn't attached to the positive rail, was 1 rail above.
Thanks again for the forward voltage description that makes a lot of sense.

 

[plutes]

the book is 30 solder less breadboard projects R.A PENFOLD there is a book 2, but not been able to find the pdf of that copy

 

[Nanren888]

Yep. A fun book. Thanks for the reminder. Also good that you had it right, all but one power supply wire.
Had a lot of fun with LM380s a while back. I do have a vague memory of them getting hot at times, but maybe I mistreated some.

 

[plutes]

The tone generator is a good one for extending upon, I'm glad this one is finished with now so I can reuse the ic on another project. That 555 question has me now reading my 555 project book, I need a die cast case now so I can make the signal injector circuit. My old college books are way to advanced and being scopeless ott