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single transistor oscillator

Started by Vivek N October 24, 2013
I tried building a single transistor LED flasher like this :

http://cappels.org/dproj/simplest_LED_flasher/Simplest_LED_Flasher_Circuit.html

I didn't have the recommended 2n2222 - I tried with a BC548, 2n2369 and 2n3055 - None of them work.

I'm using a trimpot set to 2 kiloohms and a 470 microfarad capacitor. Instead of a 100 ohm resistor I put 3 superbright LEDs in series.

I get 1.2 volts across the LED and 8.6 volts across the capacitor. My supply is exactly 12.8 volts

Does this required negative resistance effect only work with specific transistors?



On a sunny day (Thu, 24 Oct 2013 12:05:57 -0700 (PDT)) it happened Vivek N
<rep.movsd@gmail.com> wrote in
<406a189e-1b31-461b-bd76-aa0660a26bde@googlegroups.com>:

>I tried building a single transistor LED flasher like this : > >http://cappels.org/dproj/simplest_LED_flasher/Simplest_LED_Flasher_Circuit.html > >I didn't have the recommended 2n2222 - I tried with a BC548, 2n2369 and 2n3055 - None of them work. > >I'm using a trimpot set to 2 kiloohms and a 470 microfarad capacitor. Instead of a 100 ohm resistor I put 3 superbright LEDs in >series. > >I get 1.2 volts across the LED and 8.6 volts across the capacitor. My supply is exactly 12.8 volts > >Does this required negative resistance effect only work with specific transistors?
Does not look like a very reproducable circuit. Better use an unijunction transistor or even a 555 timer, or a simple 2 transistor multivibrator.
On Thu, 24 Oct 2013 12:05:57 -0700 (PDT), Vivek N
<rep.movsd@gmail.com> wrote:

>I tried building a single transistor LED flasher like this : > >http://cappels.org/dproj/simplest_LED_flasher/Simplest_LED_Flasher_Circuit.html > >I didn't have the recommended 2n2222 - I tried with a BC548, 2n2369 and 2n3055 - None of them work. > >I'm using a trimpot set to 2 kiloohms and a 470 microfarad capacitor. Instead of a 100 ohm resistor I put 3 superbright LEDs in series. > >I get 1.2 volts across the LED and 8.6 volts across the capacitor. My supply is exactly 12.8 volts > >Does this required negative resistance effect only work with specific transistors? > >
It requires the transistor to avalanche... that is, be lucky. It's crap circuit design. ...Jim Thompson -- | James E.Thompson | mens | | Analog Innovations | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | San Tan Valley, AZ 85142 Skype: Contacts Only | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | I love to cook with wine. Sometimes I even put it in the food.
On 10/24/2013 12:05 PM, Vivek N wrote:
> I tried building a single transistor LED flasher like this : > > http://cappels.org/dproj/simplest_LED_flasher/Simplest_LED_Flasher_Circuit.html > > I didn't have the recommended 2n2222 - I tried with a BC548, 2n2369 and 2n3055 - None of them work. > > I'm using a trimpot set to 2 kiloohms and a 470 microfarad capacitor. Instead of a 100 ohm resistor I put 3 superbright LEDs in series. > > I get 1.2 volts across the LED and 8.6 volts across the capacitor. My supply is exactly 12.8 volts > > Does this required negative resistance effect only work with specific transistors? > > >
Did you try to build the circuit as designed??? You can't take any diagram and substitute EVERYTHING and expect it to work. Make it work with ONE led and the proper values first. You don't have enough voltage. Add up 3x the led forward voltage plus the avalanche break down of the transistor. If you wanna build one for fun, have fun. This is an un-repeatable design. The answer to your question is YES. The effect varies considerably between transistors and among instances of the same type. The transistors on your list have such loose specs that you can sweep the floor at the plant making any transistor and they'll meet that spec. The one you happen to have may be only loosely related to any other of that type. The effect you need is not specified and can be anything. And there exists a simpler circuit that's guaranteed to work. https://www.google.com/search?as_q=flashing+led&as_epq=&as_oq=&as_eq=&as_nlo=&as_nhi=&lr=&cr=&as_qdr=all&as_sitesearch=&as_occt=any&safe=images&tbs=&as_filetype=&as_rights=
"Vivek N"
> >I tried building a single transistor LED flasher like this : > > http://cappels.org/dproj/simplest_LED_flasher/Simplest_LED_Flasher_Circuit.html > > I didn't have the recommended 2n2222 - I tried with a BC548, 2n2369 and > 2n3055 - None of them work.
** From the article: " The 2N2222 NPN transistor seems to work reliably in this circuit. Other transistors may be more temperamental, and others might not work at all. "
> I put 3 superbright LEDs in series.
** Well, that will sure as hell stop it working. .... Phil
>I tried building a single transistor LED flasher like this : > >http://cappels.org/dproj/simplest_LED_flasher/Simplest_LED_Flasher_Circuit.html > >I didn't have the recommended 2n2222 - I tried with a BC548, 2n2369 and >2n3055 - None of them work. > >I'm using a trimpot set to 2 kiloohms and a 470 microfarad capacitor. >Instead of a 100 ohm resistor I put 3 superbright LEDs in >series. > >I get 1.2 volts across the LED and 8.6 volts across the capacitor. My >supply is exactly 12.8 volts > >Does this required negative resistance effect only work with specific >transistors?
The property of the transistors that this oscillator depends on is well known and described too but as its use is way outside the scope of the specifications of any known transistor you can never design a reliable circuit with it. Though as you obviously has no knowledge of the electronics involved, you'd better start with a circuit as near as possible to the published design. As you have no 2N2222 available, another general purpose smal signal may do. Suppose this way you will find a transistor that works for you. Only then you can try to change LEDs and find out that three superbright ones in series does not work and never will. If you really want a one transistor oscillator you'd better go for a 2N2646. That's a uni junction transistor and you can find numerous examples using google. As I have no datasheet of it inside my head you'll have to find it yourself to find out how many super brights you can use in series with it on a 12V power supply. As there are single (NPN or PNP) transistor oscillator circuits FAIK there's no one really suitable for blinking a LED. A simple two transistor bistable is much better (and cheaper). petrus bitbyter
You know I may have put off some people asking how to do something wrongly, I said I don't care as long as it works. That had to do with a crossover cable and internet sharing, not destroying silicon. 

I would say that as designed, that circuit might work half the time. Secondly, it is definitely not good for the transistor. It will likely fail soon. Of course modern manufacturers don't care, but I would never build something like that. 
"petrus bitbyter" <petrus.bitbyter@hotmail.com> schreef in bericht 
news:526a84f6$0$1693$e4fe514c@dreader35.news.xs4all.nl...
> >>I tried building a single transistor LED flasher like this : >> >>http://cappels.org/dproj/simplest_LED_flasher/Simplest_LED_Flasher_Circuit.html >> >>I didn't have the recommended 2n2222 - I tried with a BC548, 2n2369 and >>2n3055 - None of them work. >> >>I'm using a trimpot set to 2 kiloohms and a 470 microfarad capacitor. >>Instead of a 100 ohm resistor I put 3 superbright LEDs in >>series. >> >>I get 1.2 volts across the LED and 8.6 volts across the capacitor. My >>supply is exactly 12.8 volts >> >>Does this required negative resistance effect only work with specific >>transistors? > > The property of the transistors that this oscillator depends on is well > known and described too but as its use is way outside the scope of the > specifications of any known transistor you can never design a reliable > circuit with it. > > Though as you obviously has no knowledge of the electronics involved, > you'd better start with a circuit as near as possible to the published > design. As you have no 2N2222 available, another general purpose smal > signal may do. Suppose this way you will find a transistor that works for > you. Only then you can try to change LEDs and find out that three > superbright ones in series does not work and never will. > > If you really want a one transistor oscillator you'd better go for a > 2N2646. That's a uni junction transistor and you can find numerous > examples using google. As I have no datasheet of it inside my head you'll > have to find it yourself to find out how many super brights you can use in > series with it on a 12V power supply. > > As there are single (NPN or PNP) transistor oscillator circuits FAIK > there's no one really suitable for blinking a LED. A simple two transistor > bistable is much better (and cheaper). > > petrus bitbyter >
Oops. Bistable should be astable. petrus bitbyter
Vivek N <rep.movsd@gmail.com> wrote in
news:406a189e-1b31-461b-bd76-aa0660a26bde@googlegroups.com: 

> I tried building a single transistor LED flasher like this : > > http://cappels.org/dproj/simplest_LED_flasher/Simplest_LED_Flasher_Circ > uit.html > > I didn't have the recommended 2n2222 - I tried with a BC548, 2n2369 > and 2n3055 - None of them work. > > I'm using a trimpot set to 2 kiloohms and a 470 microfarad capacitor. > Instead of a 100 ohm resistor I put 3 superbright LEDs in series. > > I get 1.2 volts across the LED and 8.6 volts across the capacitor. My > supply is exactly 12.8 volts > > Does this required negative resistance effect only work with specific > transistors? > > >
Look closer, the emitter is back biased ( which is a zener by nature, wide hysteresis and about 5 volts) and collector is forward biased. Reversed of normal use. You have a rc ramp voltage and as you see the flash, it is the discharging of the capacitor. Although cap voltage doesn't go to zero. cheers --- news://freenews.netfront.net/ - complaints: news@netfront.net ---
On 2013-10-24, Vivek N <rep.movsd@gmail.com> wrote:
> I tried building a single transistor LED flasher like this : > > http://cappels.org/dproj/simplest_LED_flasher/Simplest_LED_Flasher_Circuit.html > > I didn't have the recommended 2n2222 - I tried with a BC548, 2n2369 and 2n3055 - None of them work. > > I'm using a trimpot set to 2 kiloohms and a 470 microfarad capacitor. Instead of a 100 ohm resistor I put 3 superbright LEDs in series.
> I get 1.2 volts across the LED and 8.6 volts across the capacitor. My supply is exactly 12.8 volts
> Does this required negative resistance effect only work with specific transistors?
something like it it should work with most transistors. having some BC548 on hand I built it on solderless breadboard with a red LED 100 ohm and 3.9K resistors and a used 470uF capacitor, it ran at about 4Hz. according to my oscilloscope the negative resistance zone of my BC548 is only 100mV wide. it starts at about about 8.2V so you need to have 8.2V across the transistor which with a 12V supply leaves 3.8v for the the input resistor, the LED and the LED series resistor three LEDs in series is going to blow that budget, two will be pushing it, so find a 100 ohm resistor your BC548 may be different to mine. but about 12V seems like a good starting point for a supply, if it doesn't light the led increase the voltage until it starts. I'm seeing some wierds harmonic oscillations with this circuit, but I can't be sure if it's caused by my powersupply, mains pickup, or something else, all my stored 12V lead-acid batteries are dead, and I don't feel like taping 8 AAs together. I'll score some used, but still functional UPS batteries on tuesday, and maybe do some more experiments. -- &#9858;&#9859; 100% natural --- news://freenews.netfront.net/ - complaints: news@netfront.net ---