Hi All

I am working on a design, and require about 5-6 GPIO pins for various Switch operations.

But I have about 2 spare GPIO pins available.

I do not want to have I2C GPIO extender and have my system continuously poll it. But I might have one if I need additional LED GPIO.

Has anyone used an ADC with various resistors values to determined which switch has been pressed? Is there any disadvantage of this method?

 

I have used this method. It is a very effective way of reducing the number if used input pins but make sure you take into account the possibility of two switches being pressed at the same time.

 

It is a very common method for membrane keypads. If you scale the resistors 1:2:4:8:16 you can deal with multiple switch closures.
I suppose it could extend to any number of switches, but unless you have some high-precision resistors more than 5 is probably pushing your luck.
If you have changeover switches (which you probably don’t, but you just might), you can arrange to disable other switches when one is pressed, the you are not so constrained on choice of resistors.

 

Here is a novel alternative. It is more complicated than a simple resistor array but maybe it has attractive aspects:
(source)

 

Great. Yes we aim to use a membrane Keypad.

Our aim is to keep it as simple as possible as far as its possible.

There could be a possibility two key can be pressed at once, so how would scaling help involving this issue. The max switches we would need is about 6.