How do I use multiple BCD switches as a single binary input?
As you're very unlikely to find an off the shelf chip that solves a specific (but not very common) problem the chances are you will have to build something. The conversion of the BCD to binary is a simple but repetitive task and is suited to a small micro controller but the number of input/output pins required is quite large so converting the code to a serial stream with an external shift register - parallel in/serial out for reading the BCD switches and a serial in/parallel out for the output binary number will help out. You should be able to control everything with no more than 6 i/o pins on the controller (fix operation mode with a pull up/down resistor)



You'll need 14 bits to display the maximum value of the bcd (9999). The uC can just about be anything. Input through 74F676 16-Bit Serial/Parallel-In, Serial-Out Shift Register and output through 74F675A 16-Bit Serial-In, Serial/Parallel-Out Shift Register

Expanding the number of BCD switches involves adding extra shift registers and a small change in the program.