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Oct 23, 2023:
Revision: v1.2

The SugarCube+ VFO Club Project

My local radio club undertook a short run of SugarCube+ VFO kits. We encountered a few bumps on the road to success. You may find the details useful if you are thinking about doing a similar club kit-building exercise.

Figure 1 : The prototype of the radio club's SC+ VFO. It looks
large in this photo, but in fact it measures a compact 110 x 70 x 25 mm.

Background

Here in New Zealand where I live, my local amateur radio club decided to build a small number of SugarCube+ VFOs as a club project. An initial build of ten kits was seen as a suitable starting point. It was large enough to gauge interest while not requiring a lot of the club’s funds for the purchase of the necessary parts.

Construction

It was initially decided that they would be built in a small ABS plastic box. The 0.91” OLED, rotary encoder and the three pushbuttons were to be mounted on the front panel of the box. In addition, 5VDC would be supplied to the SC+ VFO via a USB-C connector mounted on one side.

A small 3.5mm socket would also be located on the side for PTT and receiver signal strength connections.
Finally, three SMA female connectors for the SC+ oscillator outputs were to be mounted on the rear panel.









Figure 2 : The original plan was to use a
small 100 x 60 x 25mm ABS plastic box like
this but plans changed as the kit was developed


Now, this is not the typical usual way the SC+ is constructed. To date, all the SugarCube oscillators use a tiny 25 x 25 mm PCB. This mounts inside the target receiver, transmitter or transceiver. The SC+ typically replaces an existing analog LC-type VFO and crystal controlled BFO/CIO. 




Figure 3 : The physical design of the SC+ assumed it would be fitted into existing equipment by the builder.



So while making it in a ABS plastic box approach was feasible, it required much more effort than you might imagine to organise 10 kits using such a box. You see, the standard SC+ on its little PCB can usually be built for less than $US10. There's not much to it. However, if you add the plastic box, the three panel-mounting SMA coaxial connectors, the USB-C and PTT'signal strenth connectors, coax, the front panel labels, the wire, nuts and bolts etc, well, the total cost very quickly increases significantly. In our case, it doubled the cost. This is something to keep in mind if you decide use this approach.

And there was another issue, too. I'll mention that shortly.

Preparing the Kits

When most people use the SC+, they mount it inside a receiver or transceiver. The rotary encoder usually replaces the variable capacitor typically used to tune the original VFO, and the switches and OLED display all fit onto the existing front panel. The switches are usually mounted on a bit of free panel space, and the associated resistors wired next to the switches.

However, in this case, the project team decided to build the front panel hardware on a prototyping board. This would then be mounted into the plastic box. This approach works well for a ‘one-off’ build but it quickly proved very demanding and time-consuming for a kit that’s assembled by builders with a mix of skill levels.






Figure 4 : A example of prototyping boards evaluated by the kit team. These were ultimately replaced by a small PCB.


It also proved difficult to get precise component alignment with this approach. This is very important when using these tiny OLED displays.

In the end, to resolve these issues, I designed a new “Switchboard” PCB for the front panel hardware. It was much easier and faster to build, and quite possibly cheaper. The time required to build the front panel assembly sharply fell to less than 30 minutes.



Figure 5 : All of the front panel components as well as the
 3V3 voltage regulator are mounted on the ‘Switchboard’ PCB
(Top - No OLED        Lower - OLED fitted)

And if all this wasn't enough, we found the first set of ten OLED displays that arrived were faulty and they all had to be thrown away.

Preparing the Box

The last stage in the process was the preparation of the ABS plastic boxes. Each box required specialized CNC milling and drilling to put the square slots in for the OLED and USB-C connector as well as the various holes for switches and connectors. It all had to be very precisely done. And no-one at our club had the skills or equipment to do it.

However, an active group of folk make use of our clubrooms for their regular 'robotics club' meeting. Mostly, this meeting of amazingly bright people discuss a miriad of other electronics and mechanical engineering topics. I briefly presented our problem and two of their attendees leapt to our assistance. They suggested laser-cutting 3mm acrylic sheet.

As an aside, it's apparently unwise to laser-cut ABS boxes. First, laser cutters don't cut ABS plastic well. ABS tends to melt leaving a messy cut. More importantly, however, the vapour given off in the process includes cyanide. So, no. It was not thought to be a good idea for this project. Let me know if your experience differs from this. Assuming you are still alive to tell me.

Anyway, by the time two further brief talks had been delivered to the group, these two helpful chaps had converted my drawings into the desired laser format on a laptop. 90 minutes, and a swift trip to the workshop later, a very attractive prototype acrylic case had been cut out and was my hands. By lunchtime the following day, I had completed the prototype you can see pictured at the top of this page.


Figure 6 : The front panel was printed in colour, trimmed, and covered with self-adhesive transparent plastic. Double-sided adhesive tape was applied to the back (spray adhesive could also be used) and then fixed onto the acrylic box front panel

Some Other Notes

The assembly of the Switchboard required the three switches to be 13mm long and the two M2 bolts to be 16mm long. The USB-C connector also used two M2x10 bolts. All four require matching M2 nuts and spring washers.

Gluing the acrylic box together requires the application of a few VERY TINY dabs of superglue or acrylic glue. Very tiny dabs. I didn't glue the base of the case. The base, and all the other pieces, are quite a neat fit, so I pressed it into place. As you can see from the photo below, the base is easily removed to allow reprogramming as required. Gravity and friction hold it in place during use.

There are also a number of pieces of hookup wire that are required in the kit. The lengths, colours and connection details are all in the instructions.


Figure 7 : Internal view of the club SC+ kit prototype. These are just visible with
the smokey gray acrylic used here. Most other acrylic colours are less transparent.

Kit Instructions

The kit, of course, required a set of instructions. These took the form of a general introduction to the SugarCube family and then led onto the detailed instructions for the kit construction. These also include the circuit diagram for the SC+ and the Switchboard. It also shows all the internal wiring details.

You can get a copy from the Download section below. You are welcome to use them for NON-COMMERCIAL USE ONLY. 

Software

One useful tool that I developed as part of this club project was a new spreadsheet. I developed a simple spreadsheet for the original SC and SC+ VFOs but these were limited to calculating the EEPROM values. The final values had to be hand-copied from the spreadsheet into the EEPROM section of the programming software (Extreme or Khazama etc).

Well, I’ve now prepared an upgraded Excel spreadsheet for the SC+ VFO which is similar to the spreadsheet tools for the SC+4, SC+16and SC+99 oscillators. This new spreadsheet allows you to enter the various programmable parameters for the SC+ VFO that are to be saved in EEPROM, and then a single mouse-click will automatically generate the EEP file for you.

This software is available for download below.


Figure 8 : The side and rear panels are used to mount the SMA connectors and the USB-C power
connector and the 3.5mm socket for the (optional) PTT and received signal strength signals.


Notes on Preparing Your Own Kits

For those interested in producing this kit for a club or group of builders, the instructions and the other material I have created are attached below in the Download section, as well as the related tools and software located elsewhere on the website. You are welcome to use this for NON-COMMERCIAL PURPOSES ONLY.

Please note that I continue to retain copyright to all this material and I retain all intellectual property rights to this and all associated material including the related SC+ firmware and software.

Frequently Asked Questions

Before you jump onto your keyboard to email me…

but.....
Other details you may require can be found on this or the other SC and SC+ pages on my website. PLEASE carefully read those pages before sending me an email. These pages include:


Conclusions and Recommendations

An enormous vote of thanks must go to those who assisted in the preparation of the initial run of kits. In particular, my thanks must go to Andrew, the laser-cutting expert. Without his help, it would not have seen the light of day.

Others at my local radio club have taken on the challenge and continued to organise kits for sale, and staff the workshops that help local buyers to build their kits. Others at the club help those with questions and with 'after-sales" technical support so I am able to focus on "the next great project".

A sincere thank you to you all.



Downloads





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