NP-41 Emulator (may be)

[Chris Chung]

(03-09-2016 07:03 PM)Harald Wrote:  Ahh, now I get it! Thanks for the explaination, that is a very clever Idea.
That way with n lines you can scan n*(n-1)/2 keys.
The conventional way it would be (n/2)^2.

The MSP430FR6989 has a lot of IO pins, the main reason to use this kind of key scan scheme is to lower the number of pins in the connector between the "brain" board and the keypad board.

As for the NP41S, the MSP430G2955 has 32 GPIO. I use the key scan scheme to reduce the key scanning pins from 14 (9+5) to 10 pins. I want to maximize the free GPIO pins I can use for expansion. The new PCB had provisions for 1) 2 pin LED backlight, 2) 1pin buzzer, 3) 4 additional SPI memory devices, 2 smd + 2 dip.

The new NP41S board came in late last week and I had assembled one quite easily, took me about an hour. I went on to print a new case (actually 2 as 1 failed) before posting here.

   

Again, I found it easier for me to operate the thing w/ no 3D printed keytop and keys, mainly because I can used the printed key legends. This half case is "head heavy" to protect the LCD module.

   

In terms of dimension, the PCB measured 68 x 120. With the 3D printed case, it's 70 x 128mm.
So it's a tad smaller than it's big brother.

   

Here is the unit outside of the case. This case is more secure as it slide / slot in and fits on the top side.

   

The back of both the case and the PCB. Most components are at the top. I had an open bottom right now so I can print fast for this prototype.

   

And a side view. The NP41S looks thinner than the NP41, the battery is placed on top side. The LCD module do adds the thickness. I may adopt a non-back-lighted version to make it slimmer in the future. The current LED backlight is very weak and mostly useless when the coin battery is run down.