HP-25C Eumulator

[Chris Chung]

(01-12-2015 09:14 PM)jebem Wrote:  Hi, Chris,
Thanks for putting me on the waiting list for the V3 NP-25.

Could you publish photos of the V3 PCB on both sides (with and without components), please?
That gives 4 photos in total.
This would help the kit builders like myself.

Thanks.
Cheers,
Jose

I don't have "blanks" now. They are all gone. I did have photos of an assembled unit closed up on the major components (i.e. not the tactile buttons).

* I made image bigger so we can see more detail

Front view below, apart from the LED modules, there are only 4 passive components. From left to right, a 104 (100nF), 47k pull-up, 102 (1nF), and 1k. Components are marked so for the caps just match 104 and 102 markings. For the resistors you have to read the colored rings or use a multimeter.

• A square pad on the PCB means the pin 1 position. Under the LED module, there is one pin marked w/ a white dot, and it's the pin 1 position, so that pin should go into the square pad.
• The 100nF is just a bypass cap for the MCU.
• Next should be a 47k (yellow + purple + black + red + brown) pull-up resistor. For the last few units / kits I had 56k (green + blue + black + red + brown) instead as I had no 47k left. The pull-up value is not that important.
• The 1nF and the 1k are more important as they form a RC delay circuit for the shift register. use a multimeter or match the ring colors w/ the photo here. (the 1k should have brown rings on both sides, i.e. brown + black + black + brown + brown = '1' '0' '0' * 10^'1', '1'% tolerance)
  

Moving to the back side there are only 2 ICs to worry about. Just follow this orientation. Some ICs have a dot on pin 1. But most DIP device uses a notch to indicate the top of the chip, and pin 1 is always the top-left pin. Again, the square pad on the PCB is pin 1.


The following illustrates what you need to do with the tactile buttons. You will need a pair of long nose plier and bent the smd pins. Then fit them into the holes on the PCB. This batch of PCB has slightly larger holes and they wobbles a bit. You can use a ruler for easier alignment (see a photo I post earlier). You can also see the white dot (pin 1) for the LED module here.


This is a side view of the test unit I used to verify all the parts for the kits. The LEDs are friction fitted (not soldered) and I had sockets for the ICs so everything (well, the expensive parts) is removable.
It works well on its own. So if you are considering savings the parts for future projects, you can do the same.


OTOH If you are soldering them all down, you will have to cut one side of the LEDs (and the ICs) short so they are inserted flush.
If you are soldering the ICs 1st, you can cut one side of the pins after your solder.
You can then friction fit the LED modules, turn on / test the unit before trimming down pins on the inner side and do final soldering.


I emphasized the final step as the double side component design, once soldered, the LEDs and ICs are permanent and there is no fixing. So It is better to fit, align, adjust, before final soldering.

The LED modules are tricky, the pins are difficult to bent / adjust. It took me 10+ units to get a hold of it. And I apologies to the early buyers as they were fitted worse than the recent units (including my own units).