coordinate matrix on a pic

[fergcu]

Hi, im currently working on a test rig for a new type of display that our company is developing. Essentially this display (in extreme prototype stage at the moment) is an 8x8 grid of optical dots (ie and 8x8 dot matrix). Each dot is approximately 8mm in diameter, and the same distance between each dot.

The test rig is designed to check each dot to see if it is on, how long it has taken to turn on etc. I therefore need 64 sensors. Obviously the main problem is that a pic doesnt have 64 inputs. My first thought is to do some kind of matrix array using coordinates (x,y), where there are 8 sensors per pin on the PIC, so will only be using 8 pins, but am having difficulty with the actual reality of designing it. Does anyone have any thoughts at all? have a hit a slight brick wall and would appreciate any ideas!

Many thanks,

Ferg

 

[Nigel Goodwin]

You just need an 8x8 matrix, the problem is I presume you're not using simple switches?.

You could use eight 1x8 CMOS switches to select each row of eight in turn?.

 

[motion]

You didn't mention if the inputs are analog or digital. Have you considered using 74HC244 tristate buffers and simply paralleling the output to an 8-bit port? Use a 74HC138 to select 1 out of 8 of the HC244's at a time.

 

[fergcu]

Hi Nigel and Motion,

Thanks for your reply's. However, interestingly the project has changed over the last 24 hours, and the goal is now to just control the display. I therefore need to be able to turn on and off any or all of the points at the same time. Electronics wise, the problem is still fairly similar, although instead of now getting input information, I just need to output a current of about 7ma to each 'dot'.

I have done some searches about CMOS switches but am a bit in the darkj about them still... does a 1x8 cmos switch require 5 inputs? or have i looked at this in completely the wrong way? The kind of things that my searching has resulted in is: https://uk.farnell.com/jsp/endecaSe...&Ntt=cmos switch&Ntk=gensearch&comSearch=true

Thanks for any light you could shed on this... in case you hadnt guessed, electronics isnt my strongest point (although im hoping to change that!! ;-) )

Ferg

 

[Nigel Goodwin]

Hi Nigel and Motion,

Thanks for your reply's. However, interestingly the project has changed over the last 24 hours, and the goal is now to just control the display. I therefore need to be able to turn on and off any or all of the points at the same time. Electronics wise, the problem is still fairly similar, although instead of now getting input information, I just need to output a current of about 7ma to each 'dot'.

Are the "dot's" actually LED's?, is so it's simple to do, you need two 8 pin PIC ports and multiplex the display as an 8x8 matrix. I would suggest using PNP transistors for the top side switching, and NPN ones for the bottom side, with suitable current limiting resistors.

 

[fergcu]

no, its probably best to think of them as little heat pads... but they are connected in the same way as led's.

I will look into multiplexing... I have found one site which describes multiplexing in the format of "Building Dot Matrix Graphic Panels with the MAX6952 and MAX6953 5x7 LED Drivers"... this should get me started.

Thanks for the info.. Im sure i will be posting shortly either to keep you updated or cry for help!

Thanks,

Ferg.