Engineering Unit #1

A project log for NP-41 RPN Calculator

NP-41 is a hardware realization of the Nonpariel calculator simulator. It executes the original HP-41C / CV byte-codes.

Chris ChungChris Chung 10/11/2015 at 23:250 Comments

Got the keys working, will need more timing adjustment (scanning) as they are sometimes not very responsive.

I am running this on a partially depleted coin cell at around 2.85V. A 3V battery will produce too much ghosting on the LCD.

Will be designing a new PCB to move on. The charge pump still fails after 1/2 second. It drops to 1.66V instead of staying at 2.8V. I had tried different values and types of capacitors and still cannot get it to work. I had also ripped the capacitor pad off after excessive re-flows. Will include more options in a new PCB design for charge pump trials (also allows custom biasing to see if contrast can be improved.

Also found out that the current design w/ the use of a port 9, I cannot assign the "ON" key the role of h/w interrupt after getting into deep sleep. So the current unit does not have a good power saving sleep scheme.

I am just showing the video here as there is a lot of interest for it. My next PCB will just contain the MCU and LCD, plus a 9-10 pin connector to a keyboard. This will save cost at the current stage.

The final unit (for this PCB) is a bit large for my liking. I was indecisive when doing the LCD and had chose to match the HP-41C LCD size. It appears that based on that the product is more likely a desk unit (a slim one though) instead of a pocket unit.