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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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