I am using AT89s8252 in my project. I have to connect 64 relays i.e in 8*8 matrix to the MCU.
I have 16 dedicated i/o pins to the matrix,specification of relays are current=12 to 14mA, voltage =12 v dc . PLZ Help ME............

 

There is a way to do this like the drawing, just scale for 64 you float the pins you don't want on

 

Hi. I could not understand the figure properly. Which pins are to be connected to rows & columns. Plz simplify this.

 

|____________rows
|
|
|
|
columns

How hard is that ?

Normally rows are horizontal lines, and columns are vertical line

This would be up to you seeing you didn't post any thing to show what your doing.

Plz simplify this

It's pretty simple you have to block the current with a diode to keep the coils off on the relays that you don't want on.

Or they would back feed and all come on.

The 12 volt is going to give you trouble because it not logic level and EMF

The simple fix would be to use 16 more relays that could have back emf diodes on them

 

The matrix solution be80be works great if you only need one relay on at any given time. Is that the case? I didn't necessarily get that from the original post. If it is not the case, his solution will not work.

 

You need to add freewheeling diodes around each relay. Then to operate any arbitrary pattern of relays, you use a voltage of approximately 100 (!!) with transistors to match, and run the "rows" (could be "columns") at a 1/8 duty cycle, at a rapid enough cycle rate that the current through the relay coils is more or less constant. Since they're inductive, this isn't too difficult.

 

The drawing I posted works quit well I made a small matrix with 4 relays there no spikes
when turn off and you could switch any of them on .

I would use logic level relays I did with the 4 I tried

This works great can't even see a spike