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LED flasher does not work need help.

audioguru

Well-Known Member
Most Helpful Member
Try a 100k resistor.
Then with the 3V supply, the base current is only 2.3V/100k= 23uA and it saturates well only when its collector current (LED current) is only 0.23mA.
That is why I said the original 47k resistor (used with a 9V supply) has its value too high.
 

gary350

Well-Known Member
Then with the 3V supply, the base current is only 2.3V/100k= 23uA and it saturates well only when its collector current (LED current) is only 0.23mA.
That is why I said the original 47k resistor (used with a 9V supply) has its value too high.
The circuit I found online was 9v but it runs good on 3v.
 
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audioguru

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The circuit I found online was 9v.
Then with only 3V the base current with the 47k resistor is only (3V - 0.7V)/47k= 48.9uA but the transistors saturate well when their collector currents are 489uA which results in a very dim LED especially if the hFE of the transistors are a little low and the 3V battery voltage has dropped a little to 2.7V.
 

cannonball

New Member
It worked fine with a 100k. The led was dim. I changed the resistor to the collector and the led to 470 ohms. It is bright enough now.
 

eurydice

New Member
Could it be that your simulated transistors are exactly alike? How could the circuit be astable if all the components are the same?
 

audioguru

Well-Known Member
Most Helpful Member
Could it be that your simulated transistors are exactly alike? How could the circuit be astable if all the components are the same?
All the parts are rarely all the same. The transistors have a wide range of hFE, the resistors and capacitors have plus and minus tolerances that are never the same.
Besides, even in all the parts are exactly the same then a little noise from the transistors and resistors will set off the oscillations.
 

gary350

Well-Known Member
LED Flashers have been blinking for a month on 2 AA batteries. Nothing has changed still the same flash rate & brightness. It has rained almost every day for a month. PC board and batteries look a bit weathered but they still all working fine. Good I did not buy battery holders they would be rusted by now. We had snow and ice a few days, ice was on circuit boards. It is 17 degrees today and sunny. It will be interesting to learn how long these Dollar Store batteries continue to work.
 

audioguru

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There seems to be an old chip that could do this for 2 years on a coin cell, the LM3909.
No. The datasheet for the LM3909 shows a duration of only 6 months for a much larger AA alkaline cell. My LM3909 had a duration of one year using a huge D size alkaline cell.

The pigeonsnest circuit produces weak current, short duration pulses at maybe only one pulse per second so of course a tiny coin cell would last a long time.
 

JonSea

Well-Known Member
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gary350

Well-Known Member
I posted about the LM3909 and included the schematic in your link way back on the first page of this nine page thread. I don't know how you could have missed it ;)
I saw the info about LM3909 but information said it has been discontinued several year ago. Anyone that has them for sale cheapest price is $8 each some people want $50 each.

I had a Christmas card once with a Black drip of glue on the card with a hearing aid battery and LED attached that blinked for 6 months. Looked like the whole circuit was inside that 1/4" diameter spot of glue.
 
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gary350

Well-Known Member
Today I see several LED flashers are not flashing, LED is ON all the time but no flashing. Tomorrow before the tornado I need to check the batteries 1 month much be the limit for AA batteries.
 

gophert

Well-Known Member
Most Helpful Member
Today I see several LED flashers are not flashing, LED is ON all the time but no flashing. Tomorrow before the tornado I need to check the batteries 1 month much be the limit for AA batteries.

If you are lucky, the Tornado will put all of your valuable stuff in your neighbors front yard, then someone will pick it up, walk away, and you'll no longer have to worry about protecting it with flashing LEDs.
 

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