NP-41 Emulator (may be)

[Chris Chung]

A member is getting the parts to do a build (14 segment version). As it is still prototyping quality, there are a few tips / instructions needed. I am putting them here in a reply so that it could be useful in the future to others who want to duplicate this.

I am not releasing the source / PCB design at this moment. They are not good to look at (messy as usual). And whoever is interested in them can PM me.

The keypad PCB is rather straight-forward. Same technique as in NP25 where you have to bent the SMD tactile buttons w/ a pair of long nose pliers and use them to fit the thru-holes. A CR2032 battery holder also on the underside.

The current PCB has 2 missing traces (design fault, I missed them) and they need to be added back. I just use resistor legs, but any wire would also do. See below.

   

For the "Head" unit, the design is also minimal. Apart from the MCU, there are 3 x 0.1uF bypass caps, a 10uF for power and a 4.7uF for the LCD charge pump.

The MCU should be soldered 1st and be examined properly w/ a magnifying glass. I had upgraded to use solder syringes and hot air gun, and still my most recent build requires a few re-flowing, caused by uneven solder paste application.

The LCD glass, do require some attention, to fit the layout, some 5 pins in the middle need to be bent (see various previous photos) and solder as surface mount.

   

To connect the 2 PCBs together, I am using common 0.1" header pins. My original idea is to allow tryouts of having the head unit tilt up better viewing angle.

I did not plan ahead when I solder the head unit (the keys PCB was not done when I do this), I had solder the female header too far from the PCB edge, I am using a thru-pin female header as SMD (for cost and availability reasons) and I should have position it close to the edge.

The result is that the male pins from the keys PCB could not fit reliably w/ the female side. Eventually I had to reshape the male pins (they are right angle pins) to extend and lower them for head unit fitting.

   

So to sum it up, my advice would be

• Solder MCU 1st, check the work and see if reflow is needed.
• Solder other parts EXCEPT all header pins and LCD.
• Play w/ the LCD and decide if and how much elevation is needed. This is similar to NP25 as parts on both sides interfere w/ each other. My build had the LCD elevated 1.5mm. Insert LCD, insert the 4 pin header for programming, the female headers (if part of these pins goes thru the PCB). decide the best fit before soldering.
• Solder the LCD, I would just solder 2 or 3 corner pin only at this stage.
• Layout both PCBs and trial fit the 2x 8 pin header connections. Decide and fix the female headers.
• Solder header pins.
• Solder reset of LCD pins.