The benefits of prototyping, even the smallest of designs.

 

As the existing stock has being cleared, it needs to be replenished, progress has been made to do this. The Retro ATX adaptors (not Amiga specific now), have been prototyped and the first two prototypes assembled as shown here

New_ATX_2015-medium

On the left is the small form factor design, primarily aimed at the picoPSU ATX power supply. On the right is the multi-purpose ATX adaptor (formerly Big Box), aimed at higher power systems and those that require additional features, notably -5V supply, 50/60Hz mains tick and AC fail status.

Some of my regular customers will notice a move away from the Amiga specific titles. The reason is simple, these adaptors will work with multiple retro systems, a name change can help generate more sales and of course happy customers. This has in part been driven by feedback from customers, asking if these adaptors work with other systems, the answer is yes. If you have a vintage retro system, with a 1980’s power supply, you may be at higher risk of power supply failure due to aging effects due to heat and dried up electrolytic capacitors. Replacing your old power supply can provide some peace of mind.

I will provide details on wiring up these adaptors for various Retro systems, including the BBC Micro, Apple II and Sam Coupe among others on my website in due course. It is not viable for me to supply power adaptors for systems that require a 9V DC supply, like the Oric Atmos or Sinclair Spectrum, as you can easily purchase modern switchmode converters.

For low power systems, I recommend a genuine picoPSU adaptor, manufactured by Mini box. Unlike most high power ATX adaptors, these converters have no minimum load requirement and are silent. A typical 230W+ power supply will have a minimum load rating, to ensure the outputs are stable so to use a regular 230W+ power supply with a retro system, using 25W, you need load resistors, sometimes dissipating upto 25W of power!

The prototype PCBs were ordered from a local company, Ragworm, hence the orange silk screen. The build quality was very good and it took me just over an hour to assemble the boards. As the aim was to get these PCBs assembled by a contract manufacturer, the existing designs needed a few refinements. All components are now on one side of the PCB, this reduces the number of process to 2 (SMT load top side and hand solder) from 3 (+SMT bottom side). This saves on the recurring costs. The control electronics have been simplified, reducing the part count. All control is now via a Microchip PIC10F202 micro-controller in a tiny 6 pin SOT023 package (3mm x 3mm), programmed on card via an ICD 3 programmer. This allowed for easy configuration for momentary or latched power switches and improved de-bounce compared to the previous design. It also provides a 50/60Hz square wave output, useful for some Amiga models that require a mains ‘tick’ signal. Finally the design also switches on/off the supply.

On both boards, I have added extra, larger, pads for connecting your own power wiring in addition to a 2 pin header. On the multi-purpose adaptor, the number of +5V and 0V connections have increased from 2 to 4, making it easier to connect to a high power, 100W+, system (mainly Amiga 2000/3000/4000). Simple changes that were easy to implement.

What did I learn from these prototypes?

For the Multi-purpose adaptor, the text describing each power rail, by the screw terminals, should be rotated 180 degrees, making it easier to read when wiring up. The linear -5V regulator needs more copper area to act as a heatsink.

Order your programming cables long in advance! To program the PIC micro and save on recurring costs, I decided to use a Tag Connect, TC2030-MCP-NL programming cable, this only requires a tiny PCB land pattern on the PCB. It may not seem much, adding a 20p, 1.25mm connector to each PCB but on a batch of 200 PCBs, it certainly adds up. The annoying part is getting hold of the cables. I currently have a cable on back order from Farnell, expected delivery date is 10th August! Finding stock in the UK has been tricky.

The other prototype PCB has been the V2.5 Amiga floppy adaptor shown here:

New_Floppy_2015-medium

This board showed the benefits of prototyping. You may notice the orientation of the drive connector is odd?
I designed this board to have a reduced form-factor to easily fit behind the floppy drive, adjacent to the drive, this did not work. The problem was that some drives, like the Mitsumi drives in my collection, have the +5V power connector above the 34 way IDC connector. So with the PCB plugged in, you can not connect the power, oops.

This new PCB is 60x24mm, the previous (V2.1) PCB was 53x40mm. The ideas was to make it smaller to fit more easily inside the Amiga and to allow easy assembly into a case to act as an external DF1 floppy drive, either with a real floppy drive or with a HxC or USB (Gotek) virtual drive. Moving the design to Little Logic and 0603 surface mount components allowed me to make the PCB much smaller.

As well as the mechanical error with the power connector, it also highlighted a limitation of the Design Rule Checks (DRC) that I run on the PCB data. One of the floppy drive connectors (the white one in the photo) is too close to a couple of resistors, this could easily be damaged in assembly and would limit inspection and rework.

The production PCB will be 5-7mm longer and the same width as the IDC box header, the two jumpers, one on either side will move into the extra space.

I am learning how to use mechanical 3D design tools (Sketchup and 123D), as an electronic engineer, they have taken some learning. I do want to master one or both tools as a 3D printer is on my wishlist. Sometimes you can’t beat a real prototype though.

The PCBs shown above need further testing before I release them for manufacture in batches of 100 of each design. The lessons learnt, minor in some cases, from these prototypes has been invaluable. Once the design release is complete I can get back to my other projects in earnest. Until the next post.

Ian

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Working away, making some progress

Hi,

Sorry for the lack of updates recently, life, the universe and everything else has interfered.

I want to discuss the following topics in this post:

Progress
Pre-orders
Extra features (avoiding feature creep)

Progress on Project Hermes

It’s continuing at a reasonable pace. I am behind schedule but I have defined a list of 15 critical tasks that need to be completed before a prototype PCB can be sent for manufacture. I have currently ticked off 3 items.

A diversion, now a planned task, was the IDE interface. The original idea was to utilise the IDE68K design as-is. This has not proven to be the case. When drawing out the schematic I noticed that a few 68EC020 signals were missing. After re-reading the manual, I noticed a few differences. The MC68000 and MC68EC020 output some signals at different clock phases. So the existing design would need some tweaks. Alexh over at EAB converted the ABEL code to VHDL (my preferred HDL). When I compiled it, targeted at the XC9572, as used originally, it did not fit, it needed 74 macrocells from a 72 macrocell part. As no parts had been ordered at this stage, it was easily swapped to a 144 macrocell XC95144 device, as used for the MIA CPLD.

To verify the IDE interface and eventually the Memory Interface Adaptor (MIA) design, I need a 68020 testbench to stimulate both designs. The last time I wrote a VHDL test bench was back in the advanced VHDL training class, back in January 2012, so I’m a little rusty. One of my personal development aims for this project was to improve my VHDL/CPLD skills.

So what I thought would be an easy tasks, grew in size. I must be confident that the IDE interface and the MIA CPLD will work before committing to hardware. Reading some of the user feedback on the IDE68K design reinforces this decision.

I typically have a few hours a week for my design projects, the little details can easily take the available time but I would rather find them now when it is easier and cheaper to fix them.

Not sure If it has been made clear but the design is intended to fit inside the CD32, similar to the venerable DCE SX32. Indeed, the PCB footprint will be no larger than this, though I expect a smaller PCB.

Pre-orders

Pre-orders are not required.

I would not start a project if I could not fund it and I will not accept funding for pre-orders. The current development phase will have 3 prototype cards, that has been funded from the profits made from the current range of Amiga adaptor PCBs I sell. Ordering of critical components has commenced, the first batch arrived today and other components will be ordered shortly.

Extra features (avoiding design creep)

If it seems like I am being very harsh shooting down extra design features, I have good reason, feature creep can kill a project. It will take some time to finish the first 3 prototypes. I have added some expansion connectors to allow me to trial other ideas later but without a prototype PCB, other features are a moot point.

Some features, like making the IDE/compact flash slot accessible from the side of the CD32 are accommodatable adding network interfaces or even an SD card interface add cost and complexity.

Once I have some working prototypes, I can experiment, then other features may get added.

Cost is a big issue for the design. Of the expected £120 retail cost, around £50 of that cost is in the manufacturing of the PCB and assembly of the module.  Work is ongoing to lower the module costs.

The most expensive components are:
XC95144 CPLD, SRAM, Compact flash connector and the 5V/3.3V logic. I looked at adding a Real Time Clock, with parallel interface, it would have cost more than the CPLDs!

That’s all for now