LED/Button Matrix - Emulating with Arduino

Other Hardware LEDs and Multiplexing
1

Hello All ... I am trying to emulate button presses on a machine and received the following diagram. I need some guidance:

Should I use a multiplexer ? Or should I use the outputs directly from the micro ? This is connecting to another controller, so I may need to add relays ...

Thanks,
Brad

2

It is not too clear what that diagram actually is nor what you want to do.
For learning about a key matrix see:-
http://www.arduino.cc/playground/Main/KeypadTutorial

3

I'm sorry .. maybe I should have explained the diagram a little better. The pinout on the matrix represents a 40 pin connector.

Everything starting with a K is a switch...L is led(s).

Brad

4

If you want the arduino to effectively short out the matrix intersections you want to use a 4066 switch. You get four of these in each IC and when enabled can connect the appropriate column to the appropriate row.

The ground must be common between this system, and the arduino, and the signals on your matrix system should not be greater than 5V.

5

Thanks Mike. Is there an IC that provides isolation(in case the control voltages differ?)

Brad

6

Not as such, you will have to include an opto isolator.
Maybe even use an opto isolated FET.

7

I thought about that or relays. Any drawbacks to relays?

Thanks again.

8

Relays will take up more space and use more power. If you do decide to go that route, use reed relays, which are smaller and need less power that traditional relays. The low power requirement allows them to be driven direct from Arduino pins or shift registers. OTOH they can only switch low voltages and currents, but that isn't an issue in your application.

Alternatively, use opto-fets, e.g. http://uk.rs-online.com/web/p/products/0456383/?searchTerm=h11f1m&relevancy-data=636F3D3226696E3D4931384E4B6E6F776E41734D504E266C753D656E266D6D3D6D61746368616C6C7061727469616C26706D3D5E5C772B2426706F3D313326736E3D592673743D4D414E5F504152545F4E554D424552267573743D68313166316D2677633D424F544826.

9

Thanks dc. I was looking at a dip type reed relay here:

Brad

10

That relay has 350 ohm coil resistance so it takes around 14mA at 5v, and the opto fet I linked to is spec'ed at 16mA (although it will probably work with less). So there isn't much to choose between them.

Since you need 29 of them, you'll either need to use an Arduino Mega (and check the total current draw is within limits) or you'll need shift registers or something similar to drive them. One 74HC595 per 5 relays (to keep within the 70mA Vcc and ground current limit) is one solution.

You can also get 5v reed relays with 500 ohm coil resistance (10mA current), but the ones I found cost more than the one you linked to.

11

Thanks for your reply. I checked out the relays you are referring to. Size for me is important also since I need so many relays.

Brad