I have an outdoor numeric keypad to control my garage door opener, but the main control board was fried in a recent electrical storm, so I want to replace it by building my own with an arduino.
The issue I'm having is that the keypad only has 6 wires to interface with the controller. The keypad is 10 buttons in a 2x5 grid, so I don't think you can matrix it in a logical way on less than 7 wires (2x5 or 3x4). To further complicate things, there's also an LED on the keypad controlled from the same lines, though I can think of a lot of ways to sneak that in on the same lines as the keypad.
Can anyone suggest some schemes the designers may have used to encode the keypad and how I might go about figuring out the pinout? Some ideas that occur to me are an MCU in the keypad (but that would add a lot of cost to save 1 wire), or have the buttons on resistor ladders and use an analog input (but that's a lot more complexity to the design for very little benefit), so I would be very surprised if either of those was right.
A remote idea is that the keypad is Charlieplexed, which would need 4 lines only, but 10 or 12 additional diodes, which however is no issue in China made products.
It does not matter what part of the world something is made in. If there is a design that costs less to build, any manufacturer would rather use that design.
This is only half of the truth.
Some production steps can be performed by labor OR by machines. If you have to use machines because labor is beyond price, you are limited to what machines can do... best to glue a SOC and that's it. If labor is cheap you can do fancy things like Chinese Ivory Balls, or hand soldered arrays of discrete diodes...