[Noisebridge-discuss] Help with Simple Circuit : Blinking LED

Mike Chambers mikechambers at gmail.com
Wed Jul 28 16:16:27 UTC 2010


Yes, Tymm pointed this out to me earlier. The circuit just pulses the
LED once, and doesnt make it blink.

I found the correct circuit further down on the page:

http://tronixstuff.files.wordpress.com/2010/06/multivib1.jpg

and got it working last night. Woot!

Thanks for all of the help. Im just starting to learn this stuff, and
the feedback / input has been really helpful.

mike

On Tue, Jul 27, 2010 at 11:47 PM, Jonathan Foote <jtfoote at ieee.org> wrote:
> Jim's right, that looks like a "one-shot" timer and not an oscillator.
>
> To get something that oscillates, use a circuit that discharges the
> cap when it turns on like a multivibrator
> (https://secure.wikimedia.org/wikipedia/en/wiki/Multivibrator) or a
> 555.
>
> There are one-transistor flashers but they are sort of dodgy as they
> rely on negative resistance from avalanche  e.g. see "LED flasher"
> midway on this page: http://members.shaw.ca/roma/twenty-three.html
>
> I wouldn't count on it working reliably or for any length of time
> unless you use transistors designed to work in avalanche -- try a
> multivibrator.
>
>
>
>
>
> On Tue, Jul 27, 2010 at 10:56 PM, jim <jim at well.com> wrote:
>>
>>   seems to me the circuit fails because there's no
>> discharge path for the capacitor.
>>   assume a switch in the circuit.
>>   ground the top of the cap (just to get it ready)
>> then flip the switch.
>>   current flows until the cap has the same potential
>> as the battery (and the collector of the transistor)
>> and the base has the same potential as ground and no
>> more current flows: i.e. the LED turns on until the
>> circuit gets static.
>>   i'd love to know how to use one cap, one resistor,
>> one transistor, and one LED and make the LED blink
>> repeatedly (i.e. get the circuit to oscillate).
>>
>>
>>
>> On Tue, 2010-07-27 at 16:32 -0700, Mike Chambers wrote:
>>> I am trying to get a simple blinking LED circuit working, and am
>>> following the following schematic:
>>>
>>> http://tronixstuff.files.wordpress.com/2010/06/pic23.jpg
>>>
>>> Where:
>>>
>>> C1 = 10uF 50v
>>> R1 = 18k ohms
>>>
>>> Based on my understanding, that combination of resistor and capacitor
>>> should cycle every 1 second.
>>>
>>> I am using a 9V battery instead of the 6V.
>>>
>>> When I plug it in, the LED turns on for a flash, and then nothing
>>> happens. The LED is not burning out (I tested it after on a separate
>>> circuit). It looks like the transistor (BC548) is failing, as if I
>>> replace it, the LED will Flash, then nothing.
>>>
>>> You can see the specifications for the BC548 Transistor here:
>>>
>>> http://www.jameco.com/webapp/wcs/stores/servlet/ProductDisplay?langId=-1&productId=254781&catalogId=10001&freeText=BC548&app.products.maxperpage=15&storeId=10001&search_type=jamecoall&ddkey=http:ProductDisplay
>>>
>>> It says the max collector is 30V, but the max emitter is 5V.
>>>
>>> Does anyone see why my circuit is failing? Is it because I using too
>>> many volts for my transistor (9v instead of 5v)?
>>>
>>> I realize this is a super basic question, but im really trying to
>>> understand how this works, and how to choose the correct parts for a
>>> circuit.
>>>
>>> thanks...
>>>
>>> mike
>>> _______________________________________________
>>> Noisebridge-discuss mailing list
>>> Noisebridge-discuss at lists.noisebridge.net
>>> https://www.noisebridge.net/mailman/listinfo/noisebridge-discuss
>>>
>>
>>
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