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Control 4 switch with 2 pins
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Yaroooo:
Hello,

I've left 2 free pins on my MCU, unfortunately I can't change MCU pin package and I must control 4 switches.

I don't need a MUX to choose witch switch to open, but something like:
00 - Switch 1 Closed
01 - Switch 1 & 2 Closed
10 - Switch 1 & 2 & 3 Closed
11 - Switch 1 & 2 & 3 & 4 Closed

Is there a small package device that allow me this?

Thanks for any support!
Nusa:

--- Quote from: Yaroooo on September 26, 2019, 09:33:13 am ---Hello,

I've left 2 free pins on my MCU, unfortunately I can't change MCU pin package and I must control 4 switches.

I don't need a MUX to choose witch switch to open, but something like:
00 - Switch 1 Closed
01 - Switch 1 & 2 Closed
10 - Switch 1 & 2 & 3 Closed
11 - Switch 1 & 2 & 3 & 4 Closed

Is there a small package device that allow me this?

Thanks for any support!

--- End quote ---

That example simplifies to switch 1 hardwired, so only 3 switches left to deal with.
But if you intended to control 4 switches plus an off, then you have the problem of 5 states for 4 combinations.
I'd suggest using the two lines for data and clock and using a shift register to control your switches, plus the ability to use the switches in any combination you like.
German_EE:
A   B

0   0      Switch 1 wired permanently closed


0   1      OR gate connected to A and B with
             output to switch 2, switches 1 and 2 now closed

1   0      Switch 1 on, Switch 2 on through OR gate
             Switch 3 connected to A. Switches 1, 2 and 3 now closed

1   1      AND gate connected to A and B with
            output to switch 4. Switch 1 on, switch
            2 on through OR gate, switch 3 on
            through connection to A, switch 4 on
            through AND gate.

So, you can do this with one OR gate and one AND gate, available in a single 74HC58 IC, isn't Boolean Logic fun!

Edit: Added 74HC58 information
Caliaxy:

--- Quote from: Yaroooo on September 26, 2019, 09:33:13 am ---Hello,

00 - Switch 1 Closed
01 - Switch 1 & 2 Closed
10 - Switch 1 & 2 & 3 Closed
11 - Switch 1 & 2 & 3 & 4 Closed

Is there a small package device that allow me this?


--- End quote ---

If you only need these four combinations (i.e. you never need all four switches off), a creative solution would be to use a BCD decoder (such as CD4543B, https://www.jameco.com/Jameco/Products/ProdDS/13696.pdf).

Use segment outputs a, d, e and f to drive the switches and inputs C and A to control their state, as below (connect input D to GND and input B to Vdd):

C   A      a   d   e   f
1   0      1   1   1   1
0   0      1   1   1   0
0   1      1   1   0   0
1   1      1   0   0   0

There might be other possible combinations too.
German_EE:
Damn, that's a really neat solution, you win  :clap:
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