New features are blooming like May flowers for the Floppy Emu disk emulator. This firmware update has something for everyone!

Lisa

The emulated rotation speed of Lisa floppy disks can now be manually adjusted within a range of +/- 6 percent. This only affects the TACH signal that the Lisa uses to sense the drive speed – it has no effect on the actual bit rate which remains 500 Kbps. The speed adjustment is set after selecting “Lisa floppy” as the emulation mode. Adjustments may help some Lisa owners with hardware different from my test system and who reported disk speed errors.

Apple II

• Smartport disk images can now have descriptive names like “SMART0-game-archive.PO”. So long as the filename begins with “SMART” plus a unit digit 0 through 3 it will be used for that Smartport unit. The rest of the name is ignored.
• Added support for 40-track / 160K 5.25 inch disks
• bug fix: NIB disks can now be ejected normally

All computers with Floppy Emu Model C

The OLED display will be dimmed after 30 seconds of inactivity. Any disk I/O or user interaction will return it to normal brightness.

 
Download the new firmware:

Mac/Lisa firmware: mac-lisa-0.8F-F14
Apple II firmware for Floppy Emu Model B and C: apple-II-0.2I-F25
Apple II firmware for Floppy Emu Model A: apple-II-0.2I-F22

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I’m continuing to research options for alternative programming headers for AVR microcontrollers, building on the ideas I discussed earlier. For one-time programming purposes, the standard 3 x 2 pin 0.1 inch header is just… too big. I’m on the hunt for something that’s smaller, and that can be used on a bare footprint without actually soldering a header. The mockup above shows a 1.5 x 1.5 inch board with the options I’m considering, along with size references from a 32-pin AVR, an 0805 resistor, and a through-hole resistor.

A – The standard 3 x 2 footprint for 0.1 inch pin header.

B – 3 x 2 pin 0.1 inch footprint with zig-zag or lock hole spacing. This helps temporarily hold a header in place through friction.

C – 3 x 2 footprint for 0.05 inch pin header. It’s a lot smaller, but the hole spacing is tiny.

D – 3 x 2 pin footprint with zig-zag spacing for 0.05 inch pin header.

E – 3 x 2 pin footprint for pogo pins with 0.05 inch spacing. It’s nearly the same as C, except the drill holes are smaller. It’s designed for something like the Pogo Key, where the tips of pogo pins snap into the holes, but unlike C the pins don’t actually pass through the holes.

F – An alternative footprint for E. Two positions are holes to help align and stabilize the Pogo Key, and the other four positions are one-sided pads, so more of the PCB’s bottom side is available for other traces and components.

G – 6 x 1 pin footprint for pogo pins with 0.05 inch spacing, inspired by the Pogo ISP Micro. It’s essentially a Pogo Key with a linear layout instead of rectangular.

H – An alternative footprint for G. Two positions are holes to help align and stabilize the pogo pin adapter, and the other four positions are one-sided pads, so more of the PCB’s bottom side is available for other traces and components.

I – 6 x 1 pin footprint with zig-zag spacing for 0.05 inch pin header. Example

J – An alternative footprint for I. The six pins are split into groups of four and two, to prevent backwards insertion of the header.

K – Tag-Connect 6-pin no-legs version.

Here’s a look at the bottom side of the board. No surprises here, but just a visual reminder that the footprints using pads leave more empty space on the bottom for other purposes than the footprints using holes.

Is using pads better than using holes? I’m not sure. Pads leave the PCB’s bottom more open, but the signal routing for pads may require extra vias for switching between layers that wouldn’t be needed for holes, so it’s not a clear win. Holes also provide something for pogo pins to grip, and are the only way to use 0.05 inch header pins.

Is 0.05 inch spacing clearly better than 0.1 inch spacing? The footprints based on 0.05 inch spacing are obviously smaller, but the holes/pads are so closely spaced that there’s no room to squeeze a trace between them. The larger 0.1 inch spaced footprint is permeable to unrelated signal routing, so although it’s large, it’s not always a major impediment to board layout. The 0.05 inch spaced footprints are like walls that blocks all other signal traces.

I also see a risk of accidentally shorting neighboring holes/pads with the 0.05 inch spaced footprints. The copper of one is only about 10 mils away from its neighbor. If the programmer pins are slightly misaligned as they are lowered onto the board, a pin could land in the empty space between two holes/pads and cause a brief short circuit.

Are 6 x 1 linear footprints better than 3 x 2 rectangular ones? This is hard to answer. They’re the same total area. My first intuition was that 6 x 1 would be easier to fit into otherwise wasted space around the edges of the board. But after looking at it visually, I have an easier time imagining tucking that 3 x 2 into an unused spot than the 6 x 1.

 
And a Word About Tag Connect

Several people replied to my earlier post to say they’re happily using the Tag Connect cable. From what I’ve read elsewhere, they seem to have a loyal following. Its footprint K is arguably among the best of the options shown here. Yet I’ve almost totally ruled out the Tag Connect, for a reason that you might find silly.

The problem I have with Tag Connect is that it’s a cable and a pogo pin holder combined into a single unit. It’s designed to replace the existing cable on your AVR programmer, rather than attach to the end of the cable as with the other options discussed here. That means you have to purchase different versions of the Tag Connect cable depending on what programmer you have – one version fits the AVR ISP mkII, another fits the Atmel ICE, etc. If you’ve got a USBasp programmer, you’re out of luck, or will have to design your own adapter.

I own both an AVR ISP mkII and an Atmel ICE, so in theory I’d need to buy two different Tag Connect cables. If I wanted to have something assembled and programmed by a third party, I’d also have to worry about what model of programmer they have and whether a Tag Connect cable exists for it. The result would be a lot of hassle and equipment duplication, compared to any of the other options, where I could just snap an adapter onto the end of the existing programming cable.

Perhaps I could design my own adapter board for the generic Tag Connect cable, so any programmer’s 3 x 2 pin female header could plug into my adapter, and Tag Connect’s 3 x 2 pin female header could plug into another socket on the adapter. But this would result in twice the total cable length, which might impact signal quality and reduce the maximum possible bit rate for programming. Edit: I see that Tag Connect sells an adapter board like this for other MCUs, so maybe it’s fine and signal degradation isn’t a problem.

If Tag Connect sold something similar to the Pogo Key but with alignment pins, it would be a great option. But as things stand with the integrated cable, it complicates programming for anybody with multiple different programmers or who contracts third party programming with unknown programmer hardware.

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They say you can tell a lot about a person by looking at his work-space. I thought it would be fun to take a break from stuffing boxes today, and make a short video tour of the BMOW Lair. I’ve mentioned before that it’s not a large space – just a single room about 150 square feet / 14 square meters. All BMOW engineering development, order fulfillment, and storage is crammed into this one room. It used to be a home study, but BMOW projects and supplies have slowly taken over and there’s barely any free floorspace left. So come on, take a look inside…

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That ubiquitous six pin header for in-circuit programming of Atmel AVR microcontrollers – it’s the standard, but it’s not a great standard where size and cost are a concern. Can I do better?

Programming most AVRs requires a six wire interface, with a clock, serial in, serial out, reset, power, and ground. It’s common to include a 3 x 2 pin 0.1 inch header on any AVR-based board. Typically a keyed box header is used to prevent accidental backwards cable attachment, like the header on the Adarfruit breakout board shown above, but sometimes bare 3 x 2 pin 0.1 inch headers are used.

That’s fine for hobbyist work or building a prototype, but when building larger numbers of AVR-based boards, the 3 x 2 pin 0.1 inch header has two significant drawbacks. The first is the component cost and related assembly cost for a header that will only ever be used once, for a few seconds during manufacturing. It’s not a huge cost, but it’s still a factor when trying to minimize the cost per unit – why throw away money? The second drawback is the relatively large physical size of the 3 x 2 pin 0.1 inch connector. For small boards containing mostly surface mounted parts, the ICSP header can complicate layout and routing, or require enlarging the PCB.

Ideally we want a programming connector with these attributes:

• zero per-unit cost
• small footprint, preferably one-sided
• keyed to prevent backwards cable connections
• holds cable firmly attached to the board

Here are some options to consider.

 
Empty Footprint 0.1 inch

The simplest option is keep the standard 3 x 2 pin 0.1 inch header footprint, but don’t actually solder a header into it. When it’s time to do programming, place a 3 x 2 header in the holes, and apply some sideways finger pressure to ensure the pins make solid contact with the hole plating. It’s low tech, but it works.

A small optimization is to use a 3 x 2 pin 0.1 inch lock header footprint, where the holes for the individual pins are very slightly offset instead of appearing in a perfect grid. This helps hold the header in place temporarily with friction, so finger pressure normally isn’t needed. It’s what I do for Floppy Emu programming, as shown here:

This approach eliminates the cost of an otherwise-useless programming header, but it’s still too big and doesn’t prevent backwards insertion. And even with the lock header footprint, it’s not great at holding the cable in place for extended periods of development or debugging. The pins often slide out of the holes.

 
Empty Footprint 0.05 inch

A second option is to use an empty 0.05 inch header footprint, which reduces the required board area to just 25% of original. That’s great, and this might be a good solution. But most AVR programmers have a 0.1 inch cable, so a 0.1 inch to 0.05 inch adapter will need to be built or purchased. That’s a minor drawback, but it only needs to be done once.

0.05 inch pin headers are fairly delicate. Would they hold up to hundreds of insertions and removals, with the added forces of finger pressure or lock headers?

This solution is also not keyed to prevent backwards cable insertion, nor does it grip the cable tightly.

 
Empty Non-Rectangular Footprint 0.05 inch

If I’m contemplating building a 0.1 inch to 0.05 inch adapter anyway, there’s no reason the 0.05 inch end needs to retain the standard 3 x 2 layout. I could do something with 4 pins in one row and 2 pins in a second row, or any other kind of irregular pin spacing that would prevent backwards cable insertion. Maybe a 7 pin single row design, with one of the pins removed. This would make the footprint area slightly larger than a 3 x 2 layout, but it might be worth it to prevent accidental backwards connections.

 
Pogo Pins

Any kind of footprint with plated-through holes will hinder routing and component placement on both sides of the board. Spring-loaded pogo pins provide an alternative approach, making it possible to build a one-sided programming interface with exposed pads, similar to this:

With 0.05 inch spaced pogo pins this allows for the smallest footprint of all, but the pogo pins need to be held against the board with one hand during programming, making it awkward to use. It’s OK for a programming operation lasting a few seconds, but not for anything longer.

This simple AVR ICSP pogo pin adapter from Tindie shows one such approach:

It’s nice, but there’s nothing to help align the cable or prevent backwards connections.

For a fancier solution, there are pogo pin cables from Tag-Connect that include alignment pins and optional locking legs to hold the cable firmly on the board:

But when you include the area needed for the alignment pin holes, the Tag-Connect footprint is essentially the same area as the standard 3 x 2 pin 0.1 inch header footprint, and the size advantage is lost. And with the version of the Tag-Connect cable that has locking legs, the required footprint area is even larger. Look at this beast:

 
Conclusion

So what’s the best option? I don’t think any of them is a clear winner – they all have advantages and disadvantages. I really like the idea of pogo pins and exposed PCB pads, but the required alignment pin holes mostly negate the space savings, and I don’t like the idea of always needing one hand to hold the cable in place. For my purposes, I think the non-rectangular footprint with 0.05 inch headers is worth exploring further. I’ll see what I can cobble together for testing.

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Good news: the Daisy Chainer for Floppy Emu is finished, and working nicely in all my tests. With the Daisy Chainer, a mix of real and emulated disk drives can be combined into a single Apple II daisy chain for maximum flexibility. The real drives can be attached before or after the Floppy Emu.

I have a few Daisy Chainer boards available for sale now. Send me an email if you’re interested in getting one (use the Contact link at the page’s upper-right).

Not-so-good news: newly-assembled Daisy Chainer boards are a pain to test, and this is something I didn’t account for. A true functional test requires connecting the board to a Floppy Emu, an Apple II, and a variety of other disk drives, and then running through many different permutations of daisy chain configuration and disk emulation modes. It requires 15 minutes or more. That’s OK for a few hand-assembled units, but there’s no way I can do that for a larger production run.

To support faster testing, I’ve designed two special test boards that plug into the male and female DB19 connectors on the Daisy Chainer. These will enable some automated loopback testing of the main board using its own microcontroller. It won’t be a perfect test, but combined with some other automated tests for things like pin-to-pin solder shorts it should detect most likely assembly defects.

The problem is that in order to support the automated testing with the special test boards, I need to make some modifications to the Daisy Chainer PCB. I’ve finished that work, but I’m waiting for PCB delivery and then I need to assemble a second prototype. So it will probably be at least a month until full production of more Daisy Chainers is possible.

This is the first time I’ve ever been forced to redesign a PCB not because there was a problem with the device itself, but simply because the device was difficult to test efficiently. Lesson learned: when designing anything that you expect to build more than 10 units of, planning for testing should be an integral part of the design process.

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