Re: Simple circuit, stupid problem
- From: "john jardine" <john@xxxxxxxxxxxxxxxxxxxxx>
- Date: Sun, 21 Aug 2005 21:02:33 +0100
"Eriswerks" <eriswerks@xxxxxxxxx> wrote in message
news:1124649279.912701.68250@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
> I'm trying to build a two transistor LED flasher, as shown at
> http://www.reprise.com/host/circuits/transistor_flasher.asp. It should
> be perfectly simple, but I must be making some mistake that I'm just
> not seeing yet.
>
> When I build this circuit, both LEDs light continuously rather than
> flashing. I've tried varying the values of the resistors and caps that
> should control the timing, but it doesn't make a difference. I can
> actually pluck the capacitors right out of the circuit and both LEDs
> are still lit. I've built this thing a dozen times now from several
> different people's instructions, and I get the same result every time.
>
> The transistors I have on hand are a little mixed... I've tried
> 2N3904s, 3906s, and 4424, any of which ought to work as they're all
> NPN.
>
> Does anyone have any suggestions as to what stupid mistake I'm making
> here? I am starting to get sick of looking at this thing. Thanks in
> advance..!
>
Offhand it looks like the Leds should be flashing about 4 times a second.
Ensure the 10uF capacitors have their "+" terminals connected to the
transistor collectors. If not the caps will 'leak' and keep both transistors
and Leds on.
regards
john
.
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