NP-41 Emulator (may be)

[Chris Chung]

Apologies for the lack of update.

Been distracted w/ other little projects.

So I had the new boards for 3 weeks now. Had assembled one, failed again. The super fine trace does not agree with me and I always manage to 1) over do the solder paste, 2) short a trace or two, 3) trying to correct them w/ soldering iron, load of flux, solder wick,e tc. 4) after a few tries the tiny thin trace can stand the heat and pressure and give up, copper isolating from PCB.

I kind of feel tired w/ it and stayed away from the project until a few days ago when I assembled another board w/ my last MCU (these are costly, almost $20 ea). Again can't really control the solder paste perfectly (I think I need a solder mask made), and this time there were less shorted traces. I was able to correct them w/o destroying them. Took me two evenings though.

And the result is spectacular! With the 1st version "fat boy" PCBs, there were no contrast control due to charge pump failure, the contrast was not desirable and there were a lot of ghosting. To a point where I don't think I will want to use it. They are all gone in this version w/ the charge pump working, for now I had set the LCD voltage to 2.8V and there is very good contrast and almost no ghosting (unless you look really hard / angle it).

   

This version is a "headless" design where there is no keyboard and peripherals. Only the "brain" and the LCD. On the back side there are two 8 pin female headers, they are going to connect to a "base" board which is mainly 1) keyboard, use 9 pins, 2) power, 2 pins, 3) uart, 2 pins. There are 3 pins left for other purpose like may be a buzzer, and / or IR.

The idea is that I can try different keyboard designs and peripherals while saving my dearest parts (MCU + LCD). I got the idea from one of the DIYs Eric was showing (he had very expensive sharp low power LCDs, I think).

Show back of PCB, above is the failed unit.

   

To be honest, I am losing steam on this project. I've got the most difficult part working and the rest would be really boring. Like trying different keyboard schemes etc. So this will be put into a slower pace. It is also really difficult to build this, w/ all the SMD parts and 0.5mm trace.

I originally want to make this into another pocket calculator so that one of my children can take it and "really" use it in high school. The NP-25 looks more like a toy than calculator and she's reluctant to use it in class (although it works fine). Now the NP-41 is getting too big, and too delicate to carry around. When me and Waon did the LCD, I just decide that it's about the same size of a HP-41, which now looks enormous. Anyway, I am still very happy to be able to work out this custom LCD thing.

OTOH, there was this original "plan B", in case the 14 segment LCD does not work out. My DogM display module came and it's the right size for a pocket calculator. Actually it came more than a month ago. I worked on and off on a smaller, easier to make version.

The DogM display being narrower will make into a pocket size, I had order a 100x60mm board for it. Here is the prototype.

   

w/o the back light, the contrast is worse than it's bigger brother, as it's a graphic display. I am using a lesser chip (I like to challenge myself). This is not a FRAM chip, but a MSP430G2955 "value line", just got 56K flash and 4K ram. It is not a DIP device, but in TSSOP packaging, it will be easier to solder than the MSP430FR6989's LQFP packaging.

I think this one can address a broader audience of builders (as kits, etc) if I do it right. With a 132 x 32 graphic display, there are potentials to add bonus (like addn registers contents) features.

So that's it for now. Next move is the DogM PCB (when they arrive), and I am on and off designing a "base" keyboard PCB for the 14 Segment design.