Midnight  GPS Display Terminal




Assembly & Test Guide

NOTE:  This product is a derivative of the Midnight SNA product.  The assembly process shown here still has references to the SNA and will be updated shortly to reflect the GDT nomenclature and parts.


Fig 1:  Overall Kit
The GDT Kit consists of an anti-static poly bag containing "PCB & Parts" and the pre-milled enclosure containing associated hardware and the main display.  The GDT Overlay is also provided.


Fig 2:  Bag 1 Base Parts  (Refer to updated Parts List shown above-right.)
These parts form the base capabilities of the GDT.




Fig 4:  The Milled Enclosure Option



Fig 5:  Hardware provided in the Enclosure Option (milled and plain)



Fig 6:  Laminated Front Panel Overlay
(Label will be that of the GDT when this page is updated.)




Fig 7:  QVGA Display


Assembly Steps:

  1. Parts Inventory -- Make sure you have all parts shown in the various items picture above.  Note that you might not have purchased some of the options.

  2. PCB Preparation -- Using a fine-blade hack saw (or equiv) to cut out the "X" areas in each corner of the pcb to allow it to fit into the enclosure.  Be careful to cut "on the inside" of the lines for the corner between J7 and J2 so you  don't accidently cut the nearby trace on the bottom-side.

  3. Attach Connectors -- J1 (power), J5 (keyboard), J6 (serial), J12 (2x20 display connector), and J8 (28-pin IC socket for U1).  Note that J5 may have a metal shell, which fits into available holes.

  4. Attach Power On/Off Switch -- S1 must be mounted straight (perpendicular to board edge and flat against it. 

  5. Attach the 5V and 3.3V "voltage regulator" components (caps too) -- 5V VR1 ("462NL53B"), 3.3V VR2 ("ZLDO17-33"), C8, C9, C10, C11, C12 and C13.  Note that the "negative" side of the electrolytic tin cans are indicated with a black stripe.  Be sure you have the orientation/polarity correct, and especially for C13, which is oriented differently from the others. [NOTE:  For best heatsinking be sure to solder the large tab of the VR2 package to the pad on the PCB.]

  6. Test Board Voltages -- Apply power to the 2.1mm coaxial power connector J1 and press the S1 switch "in" to turn the board on.  Measure 12V, 5V and 3.3V at the respective marked test point (pads) near each regulator.  Do not proceed until you ensure that you have the specified voltages on the test pads.

  7. Attach U2 and U3 Integrated Circuits -- Carefully noting the pin 1 location for each IC, insert and solder U2 and U3 (the 20-pin ICs)DO NOT yet install U1 (the pre-programmed 28-pin dsPIC controller).

  8. Attach Q1 "2N7000" -- This TO92 package with its 3 leads on a "cardboard strip" is a MOSFET transistor.  Be sure to handle with anti-static care, form the leads to fit into the offset pad locations, oriented with the flat side of the transistor as indicated on the silkscreen.

  9. Attach All Remaining Parts -- Be careful to note polarity/orientation of the small SMT parts.

    • Note 1: The polarity of the speaker SPKR in upper-left corner of the pcb.  (+ sign in indicated on bottom of part.) 

    • Note 2: C4 is mounted on the bottom side of the PCB.

  10. Attach 4 PCB Mounting Standoffs -- Using the parts from the Enclosure Hardware bag, attach the four aluminum standoffs on the bottom side of the pcb, using the short 2x56 (smaller thread) screws.

  11. Attach 2 Display Mounting Standoffs -- Using the two, shorter 4-40 threaded aluminum standoffs to the top of the pcb next to J2 and J3 BNCs.

  12. Attach U5 to Bottom of QVGA Display -- Noting orientation of pin 1 on U5 (256 Kbit EEPROM), attach to the IC1 position on the bottom of the QVGA Display.


Power Up & Test  (Software version B1.0)

1.   Check DC Levels ... Before installing the dsPIC microcontroller and display module, turn on power and ensure that you measure 5V and 3.3V on the respective test pads (thru-holes) next to VR1 and VR2.  Do not proceed until you see these correct voltages. 

2.   Install U1 and Display ... With the power switch OFF again, install the pre-programmed dsPIC processor U1 and the QVGA display module, making sure the display connector is properly lined up with the connector on the PCB.  Do not install the GDT assembly in its enclosure until completing all the steps in this guide. 

3.   Power up sequence ... Insert the SD card in the slot on the bottom of the display, plug in the keyboard, and then press the pushbutton to apply power. You should see the following sequence:

a)   Splash Screen ... After a pause of up to five seconds, you should see the splash screen showing the firmware revision level and other information about the GDT.

b)   Beep ... The splash screen will be displayed for about 3 seconds, the Satellite Display screen will show and the speaker will beep.  If you are using the optional PS2 keyboard, you will also see the LEDs on the keyboard flash twice.

c)  The GDT has three main modes -- The GDT modes may be selected by tapping the Menu 'button' at the bottom of the display.

1) GPS Satellite Display --
connected to a GPS receiver with its antenna in a sky-accessible location, the GPS satellite display screen will begin showing the 'birds' and their signal strengths. A normal one-second 'pulsing' of the screen will be noticed each time that the data is refreshed.  After a few minutes the screen's "Fixed" field will indicated "3-D fix", meaning that the GPS receiver is locked onto the current time and location as received from the satellites.  (NOTE:  See "GPS Receiver Interfacing" below for details about connecting your favorite GPS receiver.)

2) Clock Display --
This mode display a constant indication of the 'locked' GPS time (UTC and local) as well as the date.  This is an easily-viewable and accurate clock for the radio bench.

3) Terminal Data Entry --
It is not necessary for normal use, but you may navigate the menus along the bottom of the screen by using a PS2- keyboard.  You'll need to ensure that the Scroll Lock is 'on'.  (Press and release the Scroll Lock key on the keyboard and observe the Scroll Lock LED turning on, indicating successful two-way communication has been established with the keyboard. The Caps Lock and the Num Lock keys and their associated LEDs should also be working.)  See the Reference Manual for full menu navigation and usage.

4.   Mounting the PCB Assembly (PCBA) in the Enclosure ... Now that everything is working, you can mount the GDT in its enclosure by carefully angling the PCBA into the milled enclosure.  It may help to push in the S1 power switch so it doesn't stick out quite as much, thus giving you a little more room. Use the four remaining 2-56 screws (7/16") to attach the PCBA through the four holes on the bottom side of the enclosure.  Some "compliance" was designed into the mounting arrangement to allow you to slightly adjust the position of the PCBA.  Start by loosening the four pcb mounting screws on the top of the board, then loosely screw in the four longer screws on the bottom of the enclosure.  Align the PCB so all connectors and switches protruding from the sides of the enclosure are centered within their cutout areas, then carefully tighten down the eight screws that hold everything together.

5.   Attaching the Front Panel Overlay ... Apply strips of double-sticky tape around the backside perimeter of the laminated Overlay.  (Scotch brand "Scrapbooking Tape" p/n 34-8700-9324-1 is perfect, but any double-sided tape, rubber cement or glue works well too.)  With the enclosure lid screwed in place, carefully place the Overlay on the front panel, ensuring that the four holes in the corners are aligned over the four black screws that mount the lid to the enclosure body.  Firmly press down on the Overlay (where the tape/glue is beneath) to ensure a sufficient adherence to the plastic lid.

6.   Calibrating the Touch Screen ... Once you have mounted the GDT in its enclosure and verified everything is still working, let's calibrate the touch screen.

a.   The calibration function is started by touching-and-holding the touch screen when power is first turned on. 

b.   When you see "TAP EACH CROSS" displayed, stop touching the screen and the first cross will be displayed.

c.   Touch the center of the cross with a stylus.  This is best done by touching the screen and dragging the stylus to the center of the cross and then raise the stylus.  The GDT records the last point touched before raising the stylus.

d.   After the each cross has been touched, another cross will be displayed.  Touch each in sequence until all nine crosses have been displayed and touched.

e.   After the last cross have been touched, the display will change to a simple Etch-A-Sketch screen with two buttons at the bottom.  Use your stylus to draw on the screen and see how close the drawn line follows the point of your stylus.

f.    If you are satisfied with the touch screen calibration, touch the EXIT button and the GDT will save the calibration data in EEPROM and start normal operation.

g.   If  you are not satisfied with the touch screen calibration, touch the REDO button and the touch screen calibration sequence will restart.

7.   GPS Receiver Interfacing ... The GDT's serial port operates using 3.3V digital signal levels and it will be necessary to match that interface to that of your GPS receiver's serial stream.  Many receivers use RS232 for the serial data stream carrying the NMEA data.  In this case you will need to use a TTL-to-RS232 converter (male or female) to match those data levels. If you are interfacing to a GPS receiver having a USB port, the common CP2102 converter will work well.  With either interface ensure that the jumper is set for 3.3V operation with the GDT.  You may also need to Set the Baud for your GPS receiver.  Many receivers operate at 1200 baud, which is the default setting for the GDT; but if a different data rate is needed you may adjust it using the BAUD RATE menu.  See the Reference Manual for instruction on doing this.


Congratulations!!! You now have a working Midnight GPS Display Terminal.
Open the GDT Quick Reference Guide and get to work!




(Image will be that of the GDT when this page is updated.)



Copyright 2019-2021 Midnight Design Solutions, LLC.  All Rights Reserved.
Page last updated:  March 22, 2021