Alt-BEAM Archive
Message #03269
To: Wilf Rigter Wilf.Rigter@powertech.bc.ca
From: Steven Bolt sbolt@xs4all.nl
Date: Fri, 14 May 1999 16:48:23 +0200 (CEST)
Subject: [alt-beam] Re: My Pagerbot
On Thu, 13 May 1999, Wilf Rigter wrote:
> I have tested the XFLED idea and the theoretical dropout voltages are (note
> Steve Bolt) spot on.
It takes about 1mA before you see a Vf of 0.6V across a 1N4148, and
5mA before Vf rises to 0.7V. Since we are talking about the current
at the point of switch-*off*, I submit that your 3906 (which is not
the driver) is getting excessive base current. It seems safe to
predict that a LED in that position will actually flash :)
I tested the solution I posted:
If you want to stay with a switch-off level (instead of a
switch-off time), increasing that level is probably the most
efficient solution. You might try a 1N4148 diode in series with
the 2K2 resistor (anode towards the 3906 base). That will make
the SE switch off at about 1V instead of less than 0.8V.
And with a 1381C as voltage detector, I measured switch-on at 2.15V,
switch-off at 0.78V. Adding the diode increased the switch-off
level to 1.06V, indicating an appropriate base current.
Best,
Steve
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# sbolt@xs4all.nl # Steven Bolt # popular science monthly KIJK #
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