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From: Phil on 16 Jul 2010 01:04
Hi,

I've built this circuit:
http://www.555-timer-circuits.com/up-down-fading-led.html

On a breadboard and I'm struggling to get it functioning correctly.
The LED just stays on..

How can you tell if the 555 timer chip is working?
From: Nunya on 16 Jul 2010 01:10
On Jul 15, 10:04 pm, Phil <ph...(a)databloc.co.nz> wrote:
> Hi,
>
> I've built this circuit:http://www.555-timer-circuits.com/up-down-fading-led.html
>
> On a breadboard and I'm struggling to get it functioning correctly.
> The LED just stays on..
>
> How can you tell if the 555 timer chip is working?

Did you tie pin 4 to pin 8?
From: Bill Bowden on 17 Jul 2010 01:34
On Jul 15, 10:10 pm, Nunya <jack_sheph...(a)cox.net> wrote:
> On Jul 15, 10:04 pm, Phil <ph...(a)databloc.co.nz> wrote:
>
> > Hi,
>
> > I've built this circuit:http://www.555-timer-circuits.com/up-down-fading-led.html
>
> > On a breadboard and I'm struggling to get it functioning correctly.
> > The LED just stays on..
>
> > How can you tell if the 555 timer chip is working?
>
> Did you tie pin 4 to pin 8?


Actually, I think pin 4 (TTL) will float high if unterminated. It's a
good idea to connect it high if not used, but should float high if
unterminated.

-Bill
From: David Eather on 19 Jul 2010 19:49
On 16/07/2010 3:04 PM, Phil wrote:
> Hi,
>
> I've built this circuit:
> http://www.555-timer-circuits.com/up-down-fading-led.html
>
> On a breadboard and I'm struggling to get it functioning correctly.
> The LED just stays on..
>
> How can you tell if the 555 timer chip is working?

The fault may be the circuit design. If the BC547 has low gain then the
circuit will never charge the cap to the required 2/3 supply voltage to
make it change state. Try changing the 220 ohm resistor to 1k - 2.2k.
Also in the original circuit substituting for the white LED with
anything other than a blue will affect performance. With 2.2k it won't
matter
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