Is it possible to have multiple resistor ladders with one arduino UNO to control ~25 buttons that may have to be pressed simultaneously?
6 analog pins each with a 4 or 5 way ladder would work. Its much easier if only one button at a timeis pressed, as such ladders of push buttons are non-linear so button combinations are complex to figure out.
I took far too long to wire up an R2R resistor ladder on a DIP header for 6 buttons.I also ordered some SIP 8 button R2R resistor ladders from Digikey for $20 for 25 of them. Much simpler. And you can have multiple button presses.
A complication is that an R2R ladder cannot just use pullups, it must be driven with symmetrical sink/source. So either use SPDT buttons/switches, or use a 4049 or 4050 CMOS inverter or buffer. Then you can put a pullup on a SPST button/switch.Pin 1 is the output that goes to the Arduino analog input. Pin 10 is grounded. All of the other pins are either connected to ground or 5V (or 3.3V if your Arduino is running on 3.3V) by the switches or a buffer driven by the switch.
A DIY ladder network is not the way to go as manually selecting resistors is arduous.The resistors are one problem the required amplifiers is a whole other story.Suggest you use a switch matrix as it would be reliable.