Perseus Posted November 18, 2005 Report Share Posted November 18, 2005 I am new to electronics but understand many principles. Very fascinating stuff.In my mind I would think it possible to control up to 256 outputs from an 8 bit input such as a parallel port controlling home automation relays/devices.I will not need all the outputs but would like to learn how to create such a project.Could someone help me with the basics and logic and get me pointed in the right direction of thinking here.Thanks very much.Scott Quote Link to comment Share on other sites More sharing options...
EdwardM Posted November 20, 2005 Report Share Posted November 20, 2005 Hi Scottstart small and build up to it...the previous post will get you initially 4 bits, building up from there (16 possibilities and beyond) There are things like the 8255 chip which will expand an 8 bit interface. Lots of PICs allow multiple I/O ports which can then be used to drive the outside world. There are many processors like the ST10 range which, if memory serves me correctly, will drive directly 114 I/O ports. There are also 8035/8041 derivatives with different ranges of I/O.I know it's not easy but you have to try to define your requirement and then work backwards to try to find a minimal/low cost solution whicih will satisfy the original problemBest of LuckEd Quote Link to comment Share on other sites More sharing options...
Perseus Posted November 21, 2005 Author Report Share Posted November 21, 2005 Thanks very much for the information.Yeah I will definatley want to eat this elephant one bite at a time. But I am hoping one way to learn electronics is find a need and find a way to fullfill it.Again thanks I will research those chips and site.Scott Quote Link to comment Share on other sites More sharing options...
MP Posted November 24, 2005 Report Share Posted November 24, 2005 One method is to use a 4 port microcontroller and connect the port pins in a matrix. 16 ground pins and 16 control pins in a matrix will give you 16x16 combinations, or 256. You would change the data direction in the code to allow for 8 of the port pins to be inputs when needed. You could insure the matrix was not effected by this with a few diodes.If using the parallel port of a pc, you could add a 8255 and associated hardware to expand it to a 24 bit input/output port.MP Quote Link to comment Share on other sites More sharing options...
Perseus Posted November 25, 2005 Author Report Share Posted November 25, 2005 Did alot of research on this topic. With all the help you gave, it steered me in the right direction.I ended up working up a simple 64 output using 9 - 74xx138 3 to 8 decodersUsing one as an address bus and the last 8 for outputting.Now I just need to research latching the outputs. I think maybe a D-latch flip-flop (if that sounds right) is the way to go.Again thanks for the brain fuel.Scott Quote Link to comment Share on other sites More sharing options...
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