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Stumped on this circuit blinking led with 1 transistor

stspringer

May 10, 2019
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Hello All,
Hope you can help me in plain easy to understand terms, I am a newbie. Thanks

http://www.electronicshobbyprojects.com/basic-circuits/blinking-led-with-single-transistor.html
I followed this tutorial and used all the components specified and the led does not blink unless I touch the base with my finger. The tutorial says to not use the base to bend it up out of the way which i did.
So anyone know why the led won't blink on its own, without me touching the base with my finger, which is not even mentioned as an option in the tutorial.
 
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Minder

Apr 24, 2015
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The base is floating! The transistor needs to be driven somehow.
They are relying on the charge/discharge of C1, I don't really see any useful purpose being served by such a circuit?
Especially as a tutorial.!
M.
 

bertus

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Nov 8, 2019
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Hello,

What is the supply voltage?
The page states that the supply voltage should be more than 9 Volts.
The circuit is based on the breakdown of the transistor.
With a lower voltage the circuit will not work.

Bertus
 

stspringer

May 10, 2019
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Hello,

What is the supply voltage?
The page states that the supply voltage should be more than 9 Volts.
The circuit is based on the breakdown of the transistor.
With a lower voltage the circuit will not work.

Bertus
Hello,
I used 12 volts DC the video uses 12 volts too a 9 volt battery and 3 volt AA in series
I used my 12 volt power supply
 

stspringer

May 10, 2019
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The base is floating! The transistor needs to be driven somehow.
They are relying on the charge/discharge of C1, I don't really see any useful purpose being served by such a circuit?
Especially as a tutorial.!
M.

The point is this circuit is supposed to blink on its own with the base not being used. I was just following the video to try it out. I don't care if it has a purpose, but it did give some unanswered questions "the base is floating!" means nothing to me without a layman's explanation. I am a newbie know nothing like you do. Thanks
 
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73's de Edd

Aug 21, 2015
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Sir stspringer . . . . . .

In that circuit, its "IFFY" situation is being the specific / chance selection of NPN transistor that you choose to use in the circuit.
All of the spec books on transistors are carefull to give the maximum voltage that you can use from the collector to emitter.
Since it is being installed BACKWARDS polarity from the manner in which it wold normally be used, thats now
being an exploratory situation..

In your situation, MY CHOICE, would be to try every other NPN transistor in my junque box / surplus electronics for scrapping, to see if they avalance at lower than 12VDC, which seems that is not the case with your current transistor selection.
Another exploratory option would be to confirm that your 470 ufd cap is of at least a +25VDC working rating and temporarily try 2 series 9 VDC batteries in place of the 12VDC supply now in circuit.

Your activation with "finger resistive bias" to the base, signifies that all is well with your wiring, you just . . .YET . . . haven't found a transistor with a low enough break down avalanche threshold.

Thaaaaasssssit . . . .

73's de Edd . . . . . .


Teach a child to be polite and courteous in the home and, when he grows up, then he’ll NEVER be able to merge his car onto a freeway.


.
 
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stspringer

May 10, 2019
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Sir stspringer . . . . . .

In that circuit, its "IFFY" situation is being the specific / chance selection of NPN transistor that you choose to use in the circuit.
All of the spec books on transistors are carefull to give the maximum voltage that you can use from the collector to emitter.
Since it is being installed BACKWARDS polarity from the manner in which it wold normally be used, thats now
being an exploratory situation..

In your situation, MY CHOICE, would be to try every other NPN transistor in my junque box / surplus electronics for scrapping, to see if they avalance at lower than 12VDC, which seems that is not the case with your current transistor selection.
Another exploratory option would be to confirm that your 470 ufd cap is of at least a +25VDC working rating and temporarily try 2 series 9 VDC batteries in place of the 12VDC supply now in circuit.

Your activation with "finger resistive bias" to the base, signifies that all is well with your wiring, you just . . .YET . . . haven't found a transistor with a low enough break down avalanche threshold.

Thaaaaasssssit . . . .

73's de Edd . . . . . .


Teach a child to be polite and courteous in the home and, when he grows up, then he’ll NEVER be able to merge his car onto a freeway.
Well 73's de Edd thank you very much for your helpful imput. I will try different NPN transistors as you suggest. Funny they don't go into specifics about the transistor. Also, I had no idea that having batteries in series would make a differance, again nothing specific about that in the tutorial. Thank you for your creative help and for not being vague.
 

stspringer

May 10, 2019
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The base is floating! The transistor needs to be driven somehow.
They are relying on the charge/discharge of C1, I don't really see any useful purpose being served by such a circuit?
Especially as a tutorial.!
M.

Minder, please read this partial reply from 73's de Edd . . . . . . Please read his "entire post too". Very helpful

"Your activation with "finger resistive bias" to the base, signifies that all is well with your wiring, you just . . .YET . . . haven't found a transistor with a low enough break down avalanche threshold."
 

Audioguru

Sep 24, 2016
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The base is floating! The transistor needs to be driven somehow.
They are relying on the charge/discharge of C1, I don't really see any useful purpose being served by such a circuit?
Especially as a tutorial.!
M.
Absolutely not!
Why does every little transistor have a maximum emitter-base reverse voltage of only 5 or 6V? Because a higher voltage will cause avalanche breakdown.
Why is the transistor connected backwards (reverse biased emitter-base)? So that it has avalanche breakdown to blink the LED.

When the transistor is connected backwards then the collector-base diode is forward-biased and the emitter-base diode is reverse biased. Then the base is not floating.
 

bertus

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Nov 8, 2019
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Hello,

What kind of led do you use?
A green or red will work, but a white led may fail, due to the higher forward voltage.

Bertus
 

73's de Edd

Aug 21, 2015
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This is just his learning experience . . . . . just as . . . . .61 years ago, I knew that I could use the base-emitter or base collector junctions of silicon transistors as LOW power zener diodes, by using the same technique.
 

twister

Feb 12, 2012
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It could be that you have the transistor hooked the right way, not backwards, and your finger is acting as a antenna and biasing the transistor on.
 

twister

Feb 12, 2012
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I just built this circuit. I used a 2222A transistor, 13.8V and 330mfd capacitor and a 500 ohm resistor, It blinked very fast, after I turned the transistor around, ha ha. With a 5.6K resistor and a 470mfd cap. it blinked at 1.5 seconds. The transistor triggered at a little over 10V. A very useful timer circuit. I built a burglar alarm using capacitor timing circuits and a 4011 nor gate. When I open the door, the first timer gives 5 seconds to switch off the alarm. The second timer let's the alarm sound for 15 minutes till it shuts the alarm off. The nor gate triggeres at 6V if I remember correctly. A 4011 could be a or gate. I forget which. I found out that just the blinking led beside the door, has stopped the thieves from breaking in.
 
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