UHF  radio control  panel  AN/ARC-164       Realizing a project from "Wolfman"

Viperpit member "Wolfman" managed to realize a two-board interface solution to the real UHF panel. At first, his design was intended for a (replica) UHF panel with rotary encoders to set the frequency, but due to requests from other Viperpit members who own a real UHF panel (which uses rotary switches), Wolfman did a redesign of the board to connect the switches.
The first finished board is called "Indication". The Indication board connects the 6-digit FREQUENCY display and the 2-digit CHANNEL display. The second board is called "Control". The Control board connects the rotary switches, other switches and potmeters of the UHF panel. Thus, this is the board that required a significant redesign to interface to the real UHF panel. Both boards have an AVR processor and the boards interconnect with a simple 10-wire ribbon cable.

I wanted to build the UHF boards, because I obtained a real UHF panel from "JJ". JJ asked me whether I could build that hardware for him too. Returning a favor, I said "yes". Wolfman realized the boards, but was not planning to provide the boards or component kits. So, every Viperpit member had to do the project on his (her?) own. My favorite circuit board manufacturer is  Olimex  , and Wolfman was very kind to generate the ".pcb" file which is all you need to let Olimex make the boards. I inquired on Viperpits whether other members would be interested in joining in this project, thus enabling some discounts due to quantity purchases ... I have ordered 8 board sets including all parts to assemble the boards for 7 members!

As I had to solder the boards for JJ and myself, it would not be much work (... that was my first mistake) if I just soldered the other 6 sets of boards as well. I contacted the other project members to ask whether they would like to have the boards completely soldered and tested (... that was my second mistake) by me for a small fee. Everybody was happy with this offer, and in hindsight I understand why. Think of some 22 diodes, 10+ resistors, one 24-pin IC all SMD components! And the usual handfull of "normal" components. Each board requires 2 to 3 hours of soldering!

Normally you start (as I just wrote) with the smallest parts first, so that would be the SMD components. However, I received all parts on Friday afternoon, and I wanted to start soldering in the weekend not waisting any time. I do not have the right tools to do the hand-assembly of the tiny SMD parts at home, so I started with the "normal" components. The SMD parts are soldered during several lunch breaks at work.

The Indication board has 5 SMD resistors on the rear side, and 5 SMD resistors and one SMD LED on the component side.
The soldering holes for the high-power resistor are too small for the thicker wire ends of that resistor. First, I bent the connection wires at the right length and then cut the wire in such a way that the resistor is a little above the baord when the wire ends are on the board. Then I hold the wire ends against the soldering holes and apply tin at both sides. The soldering hole will fill up with tin, and additional tin on the component side mounts the resistor onto the board.

Indication board - component side	Indication board - rear side

The assembly of the Control board is done in the same manner as the Indication board, thus all SMD components are soldered last. Luckily, all SMD soldering point are accessible after all "big" components are soldered!

The Control board has quite a few more SMD components: you have to solder 5 SMD resistors, one SMD LED and 13 SMD diodes on the components side. R1 is an "SMD" resistor of zero Ohm to connect the digital ground to the analog ground of the design. I just applied a bit more soldering tin to create the "zero Ohm" resistor.

This board also has too small holes in the board for one specific component: the headphones connection 3.5 mm jack. These holes are *way* to small. However, of the 5 soldering points only two are really connections. As yu can only connect a high-impedance headphones set to this connection (certainly not a standard 8 Ohms stereo headphones set!), I will solder two 1-pin headers on the board to provide a connection to the required external audio amplifier (or external audio mixer, as you have several audio sources in the pit to route to the audio amplifier).

Control board - component side	Control board - rear side

I discovered this after I had soldered all components on all boards! As you can see in the pictures of the bare boards, the not-used surface is professionally filled up as a grounding surface. However, the distance of the traces to this grounding surface is rather small and may cause a short circuit between the trace and the grounding surface. I discovered this while programming the AVR processor of the Indication board. One of the boards caused the USB port (to which my AVR programmer is connected) to shut down, because the Indication board drew more Amps than the USB port could deliver. Luckily, the USB port was not damaged, but I had to figure out why and where the short circuit condition was located. I removed the IC from the Indication board (here is one good reason to use good-quality sockets!) and used an Ohm meter to measure the resistance between the GND and the +5 Volt power supply connectio: zero Ohms! To localize the short circuit (I could not find it with bright light and magnifier glass), I cut the +5 Volt power traces at 4 locations, thus isolating the section where the short circuit must be. And even then, I could only find the section, but not the actual short circuit point (or joint). I started to doubt my soldering skills, but using a microscope at work I found a minute copper "hair" from the +5 Volt trace to the grounding surface! Cutting the copper hair with a surgeon knife under the microscope solved the short cicuit condition.
One of the Control boards had another problem: the AVR processor did not respond to the programmer. In this case, the problem was again a thin hair copper trace between the SS connection of the 10-pin header to the grounding surface.
I promised to deliver complete sets, tested and working ... I am keeping my fingers crossed, because those thin hair copper traces can be anywhere, causing the whole thing not to work the way it should!

Before you start the assembly, you have to think if you want some green perspex ("glass") between the opening in the bezel and the displays. If you decide to change this later, you will have to do a full disassembly ...

I found a very small piece of green perspex of just 1 mm thickness (this time it is a blessing to have a big junk box, different hobbies and never throw anything away). It is just enough to make a "glass" for the FREQUENCY and CHANNEL opening. If the perspex material is thicker (very common is 3 mm), I think it will fit as well -- maybe the circuit board with the displays need a few spacer rings between the board and the UHF panel.

I chose to add the perspex. It will keep out dust, collecting between the displays over time.
First I filed the opening in the bezel from Strale some 2 mm larger at both sides, as the displays need just a little more space.

Then I spray painted the bezel black, of course in several thin layers. This is also a good moment to decide whether you want the eight M2.5 screws that mount the bezel on the UHF panel (visible) to be painted black (if they are not black). The paint that I used matched fantastic with the UHF panel. It is called "heat resistant black" 650 °C.

After the black paint had dried well, I used a very fine paint brush (RC hobby shop) to draw the white pointing lines in the bezel. As those lines are cut in the surface of the bezel, I thought it would be possible to wipe off excess white paint where it should not be (that is why you must wait until the black paint is hardened).
This worked out very bad, so better forget this method. I still wanted white paint, so now I used a needle to apply the white paint. Still, I got bad results, because the droplet of white paint is still thicker than the engraved lines. After spray painted a new black layer, I found a good working solution for the engraved lines: simply scratch the black paint out of the engraved lines with a (very) small screwdriver! I like the result, and it sure is better than any white paint attempt that I have tried ...

I mounted the green perspex bezels with a small strip double-sided adhesive tape. The displays will be mounted as near as possible to the bezel, preferably against the bezel.

It is clear that the two display groups (FREQUENCY and CHANNEL) must be mounted on the rear side of the UHF panel. The height of the displayed number must of course fit within the opening of the bezel. "Strale" created a nice aluminum bezel for the UHF panel. The opening is rather small, and after a selection, I decided to used the display type LA-301MB (Digi-Key #511-1563-ND). A nice feature of these displays is that the front face is black. But the pin distance is not the common 0.1 inch, but 2 mm. I found just one supplier for 2 mm hole pitched experimenter board (Farnell #1172114), so these displays can be mounted on that board.

My first version of the FREQUENCY display group is built on a small piece of 2 mm pitched circuit board to make it fit within the opening of the UHF panel. With a stiff wire soldered onto the board I intended to mount the display inside that opening. I am a bit worried about the correct positioning of the displays behind the opening in the bezel, because the 49 (!) wires at the rear side of the small FREQUENCY display board will create quite a pulling force ...

Update
I goofed up! I received the 2 mm pitched headers from Reichelt, and what initially seemd like a great idea turns out to be no good at all. First, the displays fit nicely in the header, but it allows for some marginal "play". The result is that the displays are difficult to line up perfectly, and I think the visual aspect is essential to be correct. But even worse, the pins of the header (what normally will be soldered) is not long enough to make a reliable contact into a stacked second header. All in all, this is not a good solution. Bummer!

Given that I already built one FREQUENCY display board (and have worries how to mount it), I put it aside and start thinking about the CHANNEL display board. I had several ideas, but none of them worked out. Finally, I came up with this idea. First, I cut a small piece of 2 mm pitched circuit board that fits in the CHANNEL display opening of the UHF panel. The board is cut a little smaller than the opening so that you can position the display perfect behind the bezel opening, but intentionally kept as large as possible to enable this new method of mounting. In the middle at the short sides I drilled a 2 mm hole, and made the hole a fraction larger by "wiggling" the drill. Then I checked where the two displays must be placed. Note that the correct position is not "centered"!

Two small pieces of the 2 mm pitched board are cut to be used as "mounting flanges" on the two M2.5 screws at the corners. Now, the CHANNEL display board is put against the bezel as good as possible at the correct position. Carefullly put the "mounting flanges on the M2.5 screws to see where the hole must be drilled for the M2 screw that holds the CHANNEL display board. Drill these holes. I drilled them 2.5 mm for starters.

Remove the CHANNEL display board from the UHF panel and mount the two flanges on the M2 screws. I used an M2 ring and two M3 nuts to get the correct "spacer". Put the assembly on the UHF panel. It will probably not fit ... but almost. Check the alignment of the display, as that is what you want to be perfect. Use a thin round file to make the holes fit on the M2.5 screws with the display at its perfect position.

Finally solder the wiring. First, solder the common + connection to the four pins (the display that I use has a separate anode connection for the decimal point LED). Check every connected wire for short circuit to a neighboring pin before you proceed with the next wire! If you find a mistake after everything is soldered, you will have to remove wires to get access to the wire that needs some corrective measures. I did a visual inspection after every wired that I soldered. After all 17 wires were soldered I did an electrical check with a 5 Volt power supply and a 330 Ohm series resistor to verify that each segment lit (and only the one that I wanted to test). The picture is extra bright to show the displays. In reality the display is a lot darker.

And here is the FREQUENCY display board, second attempt. The board is a bit larger, but still has enough manoeuverability to align the displays in the opening of the UHF panel. The major improvement with this board is that it has room for two M2 screws, so that the FREQUENCY display board can be mounted on the UHF panel in a similar way as the CHANNEL display board.
The M2 screws, the board and the (white) sides of the displays are painted black with an "EDDING 3000" permanent marker. You want everything behind the bezel as dark as possible. The top and bottom of the displays is not painted, because it is not visible. Then the two M2 screws are mounted  before  the displays are soldered. The displays are then put on the board  without  soldering them. After checking that the board fits in the opening in the UHF panel, and the displays are aligned perfectly, the displays are soldered.

This is how I have put all together. You may have other ideas, and put all together in a completely different way. I would like to hear (read) what ideas you have come up with!

1^st assembly step
Put the bezel from Strale (with or without the green perspex "glass") in the opening of the UHF panel. It fits perfectly. The openings in the mounted bezel form the reference for the circuit boards of the two display groups. Place the CHANNEL display group assembly in the opening of the UHF panel. Put four M2.5 screws (length 20 mm) in the four corners of the CHANNEL opening, mounting the flanges of the CHANNEL display group assembly. Tighten the assembly with a ring and a nut. Check that the display groups is positioned perfectly. Loosen the M2.5 nuts to "fingertight" to make the necessary position correction, if needed. Finally, check that all nuts are tightened.
Repeat this for the FREQUENCY display group. Mount the FREQUENCY display group with four M2,5 screws (length 50 mm).

2^nd assembly step
As there are quite a number of wires (66 to be exact) connecting from the UHF Indication and Control board to the UHF panel, it is wise to mount the UHF interface boards fixed onto the rear side of the UHF panel. The UHF interface board are mounted using 2 simple brackets. They are just strips of aluminum, 20 x 70 mm. I used a material thickness of 2 mm, just because the shop did not have a thinner strip; 1 mm would be OK as well.

First, you drill two holes in the strip at 6 mm from the long edge (click the image for a larger picture). The strip is positioned such that the short edge aligns with the top side of the "J1" and "J2" text above the connectors on the rear side of the UHF panel. Check before you drill the two holes that the position of the aluminum strip will be such that the UHF interface board can be mounted on the strips! Again, for some manoeuvrability, drill the hole in the "middle" of the strip 2.5 mm, and the hole "at the bottom" of the strip 3 mm.

Put the two aluminum strips on the four M2.5 screws in the four corners of the FREQUENCY opening. The smallest part of the strip is towards the opening in the UHF panel. Secure the strips with an M2.5 nut. Do not tighten the nut, it is just used at this moment to keep the strips at their place.
Place the Indication board on the two strips and center the board nicely. Use a pencil to mark the drill holes in the Indication board on the aluminum strips. Put the Indication board away, loosen the M2.5 nuts and remove the two strips. Drill 3.5 mm holes at the marked indications on the strips. Remove any burrs.
If you want the brackets look "clean", use some very fine grained sand paper or steel wool, then clean with soap and warm water.

Mount two M3 screws (length 60 mm) in the 3.5 mm drilled holes. Use a washer, ring and nut to tighten the M3 screw on the strips. Do not tighten the nuts. Slide the Indication board over the four M3 screws until the board is at approximately 5 cm from the rear side of the UHF panel. If everything fits nicely, first tighten the four M2.5 nuts that mount the strips on the UHF panel, then tighten the nuts to lock the four M3 screws firmly in the correct position. You can use a drop of nail varnish (don't tell your wife or grilfriend) to secure the M2.5 and M3 nuts.

3^rd assembly step
Put an M3 nut on each of the four long screws, and position the nut at approximately 50 mm from the rear side of the UHF panel. This nut will hold the Indication board at a fixed distance from the UHF panel. The rather large distance of 50 mm is choosen because the prefabricated cable/connectors attached to the displays are a bit long and not as flexible as I would like them to be, but given their price, they are great and save a lot of time making these connectors yourself (and very likely more expensive!).
Hold the Indication board next to the UHF panel with the rear side of the Indication board facing the UHF panel. Connect the eight display connectors on the rear side of the Indication board. Before you plug a connector into the header, make a "twist" with the eight wires of the connector, so that the 8-wire bundle is curled once. Doing so looks tidier and creates space for all 8 cable bundles.
When the eight connectors are plugged on the rear side of the Indication baord you can install the Indication board. Slide the Indication board over the four M3 screws. Rotate the "distance" nuts so that the Indication board is parallel to the UHF panel. Tighten the Indication board with a washer and the 30 mm long hexagonal spacer on the four M3 screws.
Finally, connect the common anode wire of both display groups to the screw terminal marked "PWM".

4^th assembly step
The Control board is connected to the UHF panel via the headers J1 and J2. Each header consists of 3 rows of contact pins. Luckily the pins in J1 and J2 are spaced at 0.1", so 0.1" spaced headers and pins can be used to connect. Each headers has two rows of 14 pins and one row of 11 pins. Although not all pins are connected (used) on the Control board, I soldered wires to all pins. That should take care of any future developments ...

First, plug the 6 interconnection cables in the headers on the rear side of the Control board. Then mount the Control board on the hexagonal spacers and tighthen with one M3 nut. Plug the other end of the interconnection cables one-on-one on the pins of the headers J1 and J2 on the UHF panel. Check once again that the interconnection cables are well-plugged into the headers on the rear side of the Control board.
 
The Control board and Indication board are connected to each other with a 10-wire ribbon cable. Plug the 10-wire IDC header in the socket on the Indication board. Now you can make a few bends in the 10-wire ribbon cable to create a nice looking connection cable between the Indication and Control board.

Let these two pictures speak for themselves ... I like the end result!