Mounting the LCD and preparing the case.

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Well we spent the better part of a weekend preparing the case internals and mounting the LCD. All said, it turned out well enough. I am quickly learning that adapting an existing case to a new project, can in fact be just as much work as building a nice cabinet from scratch! Modern factory equipment fits together with very fine tolerances and grafting something “Alien” into said environment tends to get tricky if you’re wanting everything about the case to close back up correctly. This is a picture of the LCD mounting. This was done with small wing brackets made of PCB material. This was the second attempt, the first was with made with a set of home made aluminium brackets. Which were a failure, as the front panel could not sit flush with the case.

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The next thing to do was add some ground plane surface area to work with. So some PCB material was cut to size. Given a spray coat of protective PCB lacquer and the result looks something like this. The rig is not a large one and I’m quite concerned about having enough raw “space” for building circuits using “Dead-Bug” or “Manhattan” style. So I wanted to be able to build circuits both top and bottom. To this end I had to use the brass PCB stand-off spacers to lift the PCB material up from where it would normally mount on the chassis. So that there would be enough room underneath for circuit components. You will note that my stand-off spacers are not fixed with bolt nuts. But instead yet more stand-off spacers are used. This is because I pulled all these brass spacers from very old PC’s many years ago and for the life of me can’t find another nut or bolt to match the thread pattern! Well, at least not in my junk-box that is. No harm done. It’s functional and I had plenty.

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I didn’t have a double sided PCB board. So I simply used two sheets of single sided material back to back. Making a mental note that it is probably a very good idea to electrically join the ground-plane areas. Just so I don’t get any strange unpredictable capacitance effects. Having the top and bottom boards “separate” could make experimental life easier later on if I need to remove one or the other.

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The board underneath is not cut to the exact same size and shape as the top piece simply because it was the off-cut from the top board. Waste not, want not.

Those with sharp eyes will note that an additional rotary switch has snuck into the front panel in these photos. The original band switch was connected to a shaft that activated various PCB mounted stage switches. So when the original board was removed the knob and shaft went with it. Since I plan on all the front knobs and controls being functional I needed to replace it.

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Next I wanted to add another PCB and a power transformer to the otherwise unused area of the original receiver. This radio is going to be a home QTH desk job. So I’ve decided to try and incorporate the power supply into the radio. To this end a multi-tap transformer went atop another slice of PCB material. Power supply to be built later.

Then I needed somewhere to mount my radio logic Ardunio board. So this was done over the top of what will be the power supply underneath. All the mucking about broke a couple of wires of the LCD display. No matter. The ribbon cable is not long enough anyway. So that’s the next job.

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If one looks closely at the photo of the logic board and PSU area. You can see a problem waiting to bite the unsuspecting constructor – Hard! The left most corner of the PSU PCB material is sitting under a plastic protrusion from the front panel. This is in fact the integral front panel headphone socket. This is bending the PCB material down and placing preasure on the front panel where none should be. Look up from that point and you can see one of the front panel self-tapping screws holding the bezel in place. The result being the front panel was miss-aligned to the case body when assembled. Worse still, it resulted in that particular bezel mount point snapping off under the lateral force. So that front panel mount point had to be Super-glued back on. And it remains to be seen how strong it will be. Gluing plastics is tricky. A small section of the PSU PCB material was trimmed away with a nibbling tool to clear the headphone socket. Now the case can be reassembled and everything aligns properly.

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So the day finished looking like this. Not too bad. At least the case fits back together nicely with proper alignment. I’m probably going to need to more ventilation holes. The case by the way, is predominantly made of plastic. In this last picture the main tuning knob is held in place for the “Photo Shoot” by a blob of Blue-Tack. The tuning pot that I had available with a splined shaft to match the original knob was just not long enough in the shaft to reach. So I’ve got a couple of 100K linear pots on order with a longer spline shaft which I think will be suitable.

Next up… Fixing up the LCD ribbon cable and cleaning up the shack work bench. Now that should take a day or two!!

The Arduino logic/control board.

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My build is going to be a “Scratch Build” with no PCB. But I decided to assemble the logic on this IC experimenters board. Which looked just about ideal for the purpose and just happened to already be in my junk box.

The Arduino ATMEGA328P IC is from an Australian company called Freetronics who make all sorts or Arduino boards and add-ons. It came with the nifty little pinout sticker on top and pre-loaded with the Arduino bootloader. So I saved myself the trouble of burning an Arduino bootloader image into a blank AVR microprocessor.

No real trouble with the build excepting for the usual debugging of ‘missing links’. Wherever Farhan’s circuit called for a 50uF electolytic I gleefully installed a 47uF instead. But apart from that it was built according to the book and worked first time.

Always very satisfying to see it “light-up” and start displaying information on the LCD.

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You would think that I would be happy and leave well enough alone. But this is where I decided to modify things and got myself into trouble…

Here are two more close ups of the logic board. Both component and solder side. Never as neat on the solder side are these experimenters boards. But that’s the side you never see 😉 And it’s functional.

The three LED’s are Red for the +5v DC power rail. Yellow for serial data TX from the Arduino and Green for RX serial data being received into the Arduino. And this is where the trouble started. After installing the serial status LED’s it stopped working. I could no longer upload a new ‘Sketch’. I had borrowed the status LEDs from part of a circuit found on the internet here.

I played around with the resulting circuit a bit and nothing simple leapt out at me. It was starting to look like I’d have to connect the digital scope and try capture some serial data transfers so that I could see what was going wrong. Then I noticed that there was two fundamental differences in the TTL to Serial convertor from the Web Site above and the one on the Minima circuit diagram around transistor Q21. The Minima had a diode from the base of Q21 to ground were the internet circuit had a 10K resistor. The other difference was that the path between Q21’s collector and pin 2 (RX) on the Arduino was via a 10K resistor. But the internet circuit was a direct link with no resistor. So being lazy I quickly made both of these changes and “wham” the serial port started working again. Both directions and with pretty status LED’s.

Another very important modification was the addition of a 0.1uF capacitor between the Reset pin 1 of the AVR microprocessor and the serial port DTR (Data Terminal Ready) pin. Pin 4 on a DB9 connector. This enables the Arduino IDE to pulse a reset to the micro just before it starts a new sketch upload. This makes programming new firmware very easy, works every time, no manual intervention with the reset switch.

I’ve reproduced the original and modified circuits below.

Minima-Serial

Minima-Serial2

Step one, tear it apart!

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So we start by tearing the old girl apart and adding the contents therein to the junk-box collection. Never throw anything out if you can help it. This was what was inside at the start of the process.

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The last photo is one of the white dial marker line removed. I didn’t want to see that in front of the LCD display. Several solvents were tried to remove it. Each with cotton wool buds. What seem to be called Q-Tips in other parts of the World. Each applied carefully to the very edge of the window so that we could see the results. In the end good old “Methylated spirits” did the job of substantially removing the white line without destroying the Perspex window.

More coming soon. Next up, my Minima logic board.