NUE-PSK Digital Modem

Kit Notes

Constructing the modem yourself



Here's the latest version of the Kit Manual ...  Kit Manual, rev B2


In addition to the guidance given in the Kit Manual, here are a few extra notes that we've collected along the way.  These tips should help you get your modem assembled without incident. 


  • The flex cable used for connecting the LCD to the pc board is really short ... there's no room to spare.  (We had a heck of a time finding such a 20-wire cable and this was the only size available.)  However it will work out just fine if you follow the guidance offered in the manual, and again here.  See the photo sequence below illustrating guidance that is guaranteed to be successful.

~ Photo Guide for Attaching LCD to the PC Board ~

        (Click on photos for full-sized view)

1) You must first only partially/barely insert one end of the flex cable into the row of holes on the pcb, and have the cable angled toward the LCD area.  The wires should not be protruding through the holes to the bottom side! 
2) The flex cable should sit in the holes at a 45-degree angle before soldering.  It should stay up (as shown) while you start to solder - but if not, put solder in the rightmost hole and position the flex cable at the right angle while the pad is hot.
3) Solder the leftmost and rightmost pins on the cable (wires 1 and 20).  You need to ensure that the cable is at the 45-degree angle and is "evenly and equally inserted" (ever so slightly) into the holes such that one end is not lower than the other as it goes into the holes.
4) Solder the remaining cable wires to the pc pads.
5) Insert the other end of the cable wires into the LCD from the bottom.  Do not solder anything yet!
6) In order to maximize the cable length on this end, you will need to carefully raise the right end of the LCD such that the rightmost cable wire going into the LCD pad 20 only comes to the top of the pad and does not stick out.  Solder the wire in the pad at this position. Then do the same for the other end (LCD pad 1) and solder it in position.  The end result, as shown here, is that no wires protrude through beyond the top of the LCD board!
7) Solder the remaining wires to the LCD.
8) Bend the cable close and tight at the bottom of the LCD board such that it looks as shown in the photo.
9) Now when you gently push the LCD down, the holes will naturally be oriented directly above the four standoffs. Attach the LCD to the standoffs using four #2 screws (the small diameter ones).
10) When properly attached, the cable will have a slight "wave" or "bow" in, as shown in this photo.
11) And as seen in this view.
12) Here is an end view of the pc board showing how the encoder and mini-pot controls are properly installed, fully and completely inserted such that they are perpendicular to the plane of the PCB.  If these controls are not inserted fully, or if they are at an angle, they will not mate very well with the top case when it comes time for final assembly.
13) Here is another end view of the pc board, this time from the bottom edge, again showing how the controls must be completely insterted tot he PCB and perpendicular to it.  The same is true for the pushbutton control, shown on the left.  (Note the important orientation of this pushbutton, with its white tabs on the sides pointing left/right, and not up/down.)
16) Bottom side of the board.  Note the mounting of the smaller 1/4" nylon standoffs, the piezo, and the 4-pin P4 copnnector.


  • Insert controls all the way into the pcb ... Be sure you press the encoder, pushbutton, and (especially) the mini potentiometer R13 all the way down flush to the pcb.  The pot is the tightest fit.  If these are not inserted all the way, and perpendicular to the board, you will have trouble fitting the board into the enclosure.

  • Orientation of the Select pushbutton ... This is just an extra (important) reminder to orient the pushbutton with the white tabs on the left and right sides (i.e., one of the white tabs will be closest to Q3).

  • Aluminum LCD standoffs ... Some kits were supplied with aluminum standoffs for attaching the LCD, whereas others' standoffs were nylon.  With the aluminum standoffs, you should be care not to screw them down so hard that they cut through the soldermask and touch the close by traces.  Doing so could short the signals on the trace to ground (notably the 5V bus) and cause problems.  Normally you'll be fine, unless you use extraordinary force to attach the standoffs.

  • Different LCDs ... Most of the LCDs we provide in the kits have the "normal" black graphics & text on a grey background, with a white LED for a backlight when turned on. However because of LCD shortages from the manufacturer (Crystalfontz), we accepted some alternate LCDs from them in order to be able to make the kits available in a timely manner.  Thus some kit customers will receive a blue or yellow background LCD with white letters.  When the backlight is on, it actually looks quite attractive, as seen below ...

  • Piezo not sounding ... This is normal, as the piezo is not currently being used.  We added the piezo for a downstream feature (Morse audio output of Tx and Rx characters), which will come along in a future release.

  • Slight delay when modem turned on for the very first time ... When powering up your modem for the very first time after construction, you may experience a blank screen for perhaps up to 5 seconds.  Then the familiar splash screen and normal display operation will be seen.  This initial delay is due to the microcontroller initializing the U4 memory device.  This occurs only once, and every time thereafter the splash screen will be seen immediately upon applying power.





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Page last updated:  Jul7 24, 2008