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Subject: Re: I need an 8 to 256 decoder or equivalent
Date: Sat, 16 Nov 2002 18:01:40 +0000
NNTP-Posting-Date: Sat, 16 Nov 2002 23:01:41 +0000 (UTC)
User-Agent: tin/1.4.2-20000205 ("Possession") (UNIX) (Linux/2.4.19 (i686))
Michael F. Coyle wrote:
> "David Jones" wrote in message
>> I'm trying to use an 8 bit binary input to select 1 of 256 different
>> LEDS(I'm using leds as an example). I know there exists a 4bit input 16
>> output decoder but I don't know how to get 256 options using it with other
>> IC's. How do I make the equivalent of an 8 to 256 decoder with the least
>> discete components? any suggestions are welcome.
> You would need seventeen 74xx154's. First, wire the bottom 4 address bits
> (let's call them ADDR3 thru ADDR0) to the '154's address inputs A3-A0.
For LEDs it can be done with just two 4-> 16 line decoders, one with active
high outputs and one with active low outputs.
One chip is driven by D0-D3 and has 16 current limit resistors in series with
its outputs each feeding the rows of a 16X16 matrix of LEDs.
The second chip is driven from D4-D7 and feeds the colums of the matrix.
Obviously the viability of this for your application depends upon the load
resembling a diode.....
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