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Switch matrix (relais and opto)

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zippy

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I am trying to make a switch matrix... I need to switch some DPDT relays (max 2A) and some Optocouplers (in and out) and some power (max 12V small currents)

Does anyone knows what's the best way to do this?
I was thinking of a matrix made by fets? but how do you do this?

if I want a 8*8 matrix, I need 64 select pins... Is there a way to lower this? also multiplexing?
 
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Boncuk

New Member
If you already have an 8*8 switch matrix the maximum number of wires is reduced to 16.

You will just need to design a decoder for the appropriate action to be taken. E.g. Pressing button 36 row5 and column4 are shorted.

Boncuk
 

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zippy

New Member
If you already have an 8*8 switch matrix the maximum number of wires is reduced to 16.

You will just need to design a decoder for the appropriate action to be taken. E.g. Pressing button 36 row5 and column4 are shorted.

Boncuk
I need to be able 2 switch a 12V/2A switch

This is how I see it:


The fet replaces the switch in your design
is this possible?
 
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Boncuk

New Member
Hi zippy,

multiplexing devices is not a good idea. Depending on the number of devices to be controlled, e.g. controlling a motor it has to share the multiplexed signal with all other devices which would lead to undesired off-times.

I assumed you want to use 64 switches to switch the same number of peripheral devices which you can do with the least pin count of the MCU by using two wire I/O-expanders. Your choice of the PCA9555 is a bit low. The MAX7300 offers 28 I/O-pins.

Using 64 pushbuttons the matrix will occupy two full ports of the MCU. You just need to connect the necessary number of I/O-expanders (via 2-wire interface) to get 64 peripheral devices to work, depending on the button you press. (Toggle function must be in the software).

The I/O-expander won't care what the peripheral device is as long as the signal levels between I/O and device interface are the same.

Boncuk
 

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zippy

New Member
Hi zippy,

multiplexing devices is not a good idea. Depending on the number of devices to be controlled, e.g. controlling a motor it has to share the multiplexed signal with all other devices which would lead to undesired off-times.

I assumed you want to use 64 switches to switch the same number of peripheral devices which you can do with the least pin count of the MCU by using two wire I/O-expanders. Your choice of the PCA9555 is a bit low. The MAX7300 offers 28 I/O-pins.

Using 64 pushbuttons the matrix will occupy two full ports of the MCU. You just need to connect the necessary number of I/O-expanders (via 2-wire interface) to get 64 peripheral devices to work, depending on the button you press. (Toggle function must be in the software).

The I/O-expander won't care what the peripheral device is as long as the signal levels between I/O and device interface are the same.

Boncuk
Sounds good! This might be the right way!

Off-topic:
I was just thinking about something else (Because I was talking about a crosspoint matrix)
Can you use multiple crosspoints in one project? So you can make a 16*16 matrix by using multiple 4*4 or 2*2? is this possible?
 

Boncuk

New Member
You will need a keyboard encoder (like in a PC keyboard) to do that. On the receiver side you must decode the signals in your MCU.

Using a straight foreward 8X8 switch matrix signal tracking will be a lot easier.

A 28 pin MCU should suffice for two vacant I/O ports.

Boncuk
 
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