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Subject: LED flashing problem
Date: Fri, 10 Jan 2003 17:03:15 +0800
Organization: IMS Netvigator
X-Newsreader: Microsoft Outlook Express 6.00.2800.1106
I have 5 groups(8 in a group) of LED, I have tried to program a
microprocessor to display some status.
I used control 5 PNP transistors
the LEDs' anodes are grouped and connected to the Collector of the 5
on the other hand, i used a ULN2804A driving IC to drive the cathode so that
the signal is output is inverted at the cathodes to toggle on/off of the
my problem is the LEDs looking unstable - that is the brightness variation
can be seen even a fixed pattern rather than a changing pattern is
I would like to know if it's a electrical current problem.
the 5 control signals connect thru 3.9k resistor to the base of 2N4403, the
Emitter are connected to 5V. each collector to 8 anodes of LED
each cathode thru a 68ohm to 1 pin of the ULN2804A. the 8 input of the
ULN2804A are then to the data bus.
can anyone give me better suggestion??
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