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LED flasher does not work need help.

gary350

Well-Known Member
Thread starter #1
I got this circuit online and I'm not very surprised that it does not work. I am not smart enough to fix it. :)

LEDs appear to be ON all the time but maybe they are blinking so fast they appear to be ON all the time?

LEDs are a bargin pack 100 for $3 about 5 years ago, they don't lite up very bright, won't be easy to see after dark on fake security system.

Circuit calls for 10uf capacitors, I changed caps to 100uf LEDs still appear to be on all the time. 1 blink every 2 seconds from each light is what I want?

I tried 3v, 4.5v, 6v. new batteries.

 
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alec_t

Well-Known Member
Most Helpful Member
#2
If the component values are as shown, each LED should blink about once every 4 seconds. You could halve R2 and R3 to get closer to your target rate.
Are you sure you have the cap polarities and the transistor pinouts correct?
Is the circuit on a breadboard?
 

rjenkinsgb

Active Member
#6
Possibly try connecting another resistor, eg. 1K, from each collector to +6V ??
That will ensure a full swing of voltage as each transistor switches.

With only 6V and dubious LEDs, the collectors may not be switching to anywhere near the positive supply as it is.
 

JonSea

Well-Known Member
Most Helpful Member
#7
I searched for 2N2222 and this came up from On Semi under that part number - it's actually a PN2222A.

But the only 2N2222 data sheets I see are for a TO18 metal can.
 

JonSea

Well-Known Member
Most Helpful Member
#8
Here's a 2N2222 pinout apparently from an On Semi datasheet, but the link goes to a dead end. So use caution and be sure what you have.

Screenshot_20190113-133335_Firefox.jpg
 

cowboybob

Well-Known Member
Most Helpful Member
#10
Gary, I feel your frustration...

This particular circuit has had me flummoxed for years (yes, YEARS!)!! :banghead::banghead::banghead::arghh::arghh::arghh::woot::woot::woot:.

IT HAS NEVER WORKED! Either as a sim (both LEDs ON, no flash). 0r as a real ckt on a bread board.
1547418077573.png (Texas Instruments "TINA")
That very same circuit here.

What am I missing (if anything)?

And, yes, I have changed component values just to make sure that my math skills haven't gone kaflooey...

Anybody else care to comment?
 
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gary350

Well-Known Member
Thread starter #11
It is fixed and it works perfect on 3V with no changes to the circuit. At a distance in the dark it looks like 1 light blinding on/off once per second. The whole circuit fits on a 1" square PC board. I am going to make a dozen of these an solder wires directly to the AA batteries then put them in, trees, bushes, every where around the house. If thieves come sneaking around in the dark an see all these red lights blinking they will probably think it is some type of security system. LOL. I need to test this to see how long AA batteries last. I might need to use 2 D batteries so it blinks for several months before it dies.

 
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#12
The pin out for a 2n2222 or a pn2222 are the same and either one will work in this circuit. #1 on the pin out should be the emitter, #2 is the base and #3 is the collector. That should work.
 

JonSea

Well-Known Member
Most Helpful Member
#13
The pin out for a 2n2222 or a pn2222 are the same and either one will work in this circuit. #1 on the pin out should be the emitter, #2 is the base and #3 is the collector. That should work.
I would think so, but the data sheets I can find are contradictory.
 

gary350

Well-Known Member
Thread starter #14
Flasher has blinked all night AA batteries are doing good.

Is there a way to make this circuit automatically turn off when sun comes up?

What is the name of those devices that have low resistance in dark then high resistance is sun light?

Battery life will be 2 to 3 times longer if circuit will turn off when days are 15 hours long.
 

JonSea

Well-Known Member
Most Helpful Member
#15
It's a pity the LM3909 LED flasher chip is no longer made. It would flash a LED from a single battery for nearly the shelf life of the battery!

Here is a circuit that claims to even improve on that, flashing a single high-efficiency red LED.

The schematic is somewhat uniquely drawn, particularly the rectangular transistors - note the arrowheads outside the rectangle indicating the emitter.

Note that the ZTX869 has critical characteristics and shouldn't be replaced according to the linked description of the circuit. They are available for 90 cents each at quality 10 from arrow.com.


SmartSelect_20190114-050222_Firefox.jpg

SmartSelect_20190114-050848_Firefox.jpg
 

JonSea

Well-Known Member
Most Helpful Member
#17
Yeah, the LM3909 is available on ebay for an outrageous price, but those chips have been out of production for years.
 

alec_t

Well-Known Member
Most Helpful Member
#18
What am I missing (if anything)?
As far as the sim goes, try making the circuit slightly asymmetric, e.g change one of the resistor values ~1%. That can help to resolve the 'can't make up its mind' initial state.
If thieves come sneaking around in the dark an see all these red lights blinking they will probably think it is some type of security system.
If all you want is a flashing light then an even simpler circuit would use an off-the-shelf flashing LED
 
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#19
I have built this circuit using 2n2222, pn2222, 2n3904. It works great. Look at #8 reply and use the pinout shown there. I don't know why some data sheets show it backwards.
 

cowboybob

Well-Known Member
Most Helpful Member
#20
As far as the sim goes, try making the circuit slightly asymmetric,
Thanks for the idea, alec.

Tried it but still no change.

I tend to believe that the TINA simulator is somewhat less than ideal, at least in this case.

I've used it for beaucoup 555 circuits, some fairly complex, so I don't know what the problem is...
 

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