NP-41 Emulator (may be)

[Chris Chung]

Progress Update

This time it is the "slim" version as I call it. The PCB came more than a month ago and I managed break the COG glass. Had to wait for another order of the DOGM equivalent LCD modules. They arrived a week ago and I had assembled one "slim" unit.

       

The front and back of the assembled PCB. I had restricted the length of the PCB to 100mm to reduce cost (at least for the prototypes) I am planning to lengthen it to 120mm so the buttons will spread out a bit and it will be more usable.

   

I also trial fit 3d buttons and a front panel. After several trials the result is quite nice. And I had confidence to make this into an everyday shirt pocket calculator. Next step is to extend the front panel to cover the LCD module (w/ a rectangular cutout, of course) and to print a back panel.

Will also have to workout the overlay / function template, etc.

   

This unit consumes 2.5mA on a CR2032 button cell active. I measure between 2.48 to 2.52mA under constant usage. There is still something wrong w/ the sleep as I envisage it to be sub-uA if not even lower (spec says 0.1 uA on RAM retention sleep). So there is more firmware work to be done.

I also experiment w/ two startup mode where one would show 3 of the stack registers, just to play w/ the possibility w/ having a graphic display.

   

You will see that this unit is head-bulky, as I am using pin sockets for the LCD module. The most expensive part in this build is the LCD so I am saving it for the final design. Just image that the finished unit will be lowered (1/2 thick) and should more or less flushed after applying the 3d printed button panel.

I really want to get rid of the LCD backlight to make it even slimmer. But my supplier only have ones w/ backlight. If I order from North America supplier, it will be $30 bucks instead of $12. So I guess I will settle for backlight for now.

Here is a video that will show the design better. Performance is similar to an original HP-41C/V. It has potential to double the speed by running at 16Mhz vs 8Mhz, but that I need to throw in 2 x 3V coin cell and have a regulator. Not sure If I want to do that.