tobychuiI receive a few DM mentioning that they want a budget numpad based on the CH552G. I am like: Why you need a numpad?
After chating with one of the person who send me a DM, I notice many mechanical keyboard users don't actually have a full sized keyboard. Instead, they would go with a keyboard without numpad, then buy an additional numpad and only took it out when they needs a numpad.
However, consider the CH552G. In this project, I am using
- 2 GPIO for LEDs
- 4 GPIO for key switches
- 3 GPIO for RGB
- 1 GPIO for mode toggle
So in total there are only 10 GPIO I can use. Is this even possible for me to build a fully functional numpad?
Maybe Yes, However
In theory you can use a grid layout to multiplex the number of switches by scanning them line by line. However, conversion design will takes in one diode per switch, which is really expensive in term of soldering jobs. I gonna need to find a way to make it under $5 if I am gonna make one myself :D
Anyway, if you really want a $5 numpad keyboard, feel free to let me know!
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" In this project, I am using 2 GPIO for LEDs [...] 3 GPIO for RGB"
You could cut this down to just 1 GPIO if you used a chain of WS281x RGB LEDs instead, which would give you 4 extra GPIOs to use for selecting rows, allowing up to 16 switches. Alternatively, you could switch to a CH552T, which I believe has 4 additional GPIOs (? I haven't read the datasheet fully, but a quick look at the pin layout suggests all 4 of the additional pins are available for use as GPIOs) and I can see suppliers in the UK who have them for only 40c over the cost of the CH552G, so I presume the extra cost from a Chinese supplier is minimal. The extra diodes required don't tend to be difficult (I just did a 16-key macropad using an ATmega8u2, and didn't find it hard, although given that that's a $4 MCU I obviously didn't manage to get it in as cheap as $5 :) )
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