LED flasher does not work need help.

Status
Not open for further replies.
cannonball said:
Try a 100k resistor.
Click to expand...
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.
 
audioguru said:
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.
Click to expand...

The circuit I found online was 9v but it runs good on 3v.
 
Last edited:
gary350 said:
The circuit I found online was 9v.
Click to expand...
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.
 
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.
 
Could it be that your simulated transistors are exactly alike? How could the circuit be astable if all the components are the same?
 
eurydice said:
Could it be that your simulated transistors are exactly alike? How could the circuit be astable if all the components are the same?
Click to expand...
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.
 
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.
 
There seems to be an old chip that could do this for 2 years on a coin cell, the LM3909. Here is a circuit that could be used instead of the IC - **broken link removed**
 
shortbus= said:
There seems to be an old chip that could do this for 2 years on a coin cell, the LM3909.
Click to expand...
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.
 
shortbus= said:
There seems to be an old chip that could do this for 2 years on a coin cell, the LM3909. Here is a circuit that could be used instead of the IC - **broken link removed**
Click to expand...

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
 
JonSea said:
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
Click to expand...

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.
 
Last edited:
JonSea said:
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
Click to expand...

As TCM used to tell me, I'm dumb and can't read.
 
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.
 
gary350 said:
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.
Click to expand...


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.
 
Status
Not open for further replies.

Similar threads

How does this generator work ?
2
Replies
32
Views
3K
ZipZapOuch
N
Led Matrix 64x64 & ESP32 Help
Replies
8
Views
535
danadak
  • Question
Help! Does anyone knows Copper paste plug hole?
Replies
7
Views
837
ian.herh
A
  • Question
Need help to identify part
Replies
11
Views
878
AdiMacG
A
D
  • Question
W1209 temperature controller not working
Replies
2
Views
1K
derekoak
D
Menu
Log in
Register
Cookies are required to use this site. You must accept them to continue using the site. Learn more…