Looking for a discount on a Floppy Emu Deluxe Bundle, and want to spread some holiday cheer at the same time? BMOW is running a holiday promotion called Get 10 Give 10. Use the coupon code GET10GIVE10 during checkout, you’ll save $10 off a Floppy Emu Deluxe Bundle, and I’ll donate a further $10 to Samaritan House of San Mateo. It’s a chance to save money on retro computer hardware and do something good for the world too.

Floppy Emu is a floppy and hard disk emulator for classic Apple II, Macintosh, and Lisa computers. It uses an SD memory card and custom hardware to mimic an Apple floppy disk or hard disk drive. It’s perfect for booting your favorite games, transferring files from vintage to modern machines, and troubleshooting a computer without a working OS. The deluxe bundle includes the Floppy Emu, an acrylic case, and an SD card with a collection of vintage Apple software disk images. Full details are available here.

Samaritan House provides food, shelter, healthcare, housing, financial assistance, and more to low-income and homeless persons in the San Francisco Bay Area. Even in the midst of Silicon Valley’s affluence, there are many people struggling just to meet the basic needs of daily life. A small boost at the right time can help them regain self-sufficiency. Samaritan House operates a broad variety of free services and one-on-one assistance with caring staff. I’ve seen first-hand what they can do, and it’s amazing.

If you’ve had your eye on a new Floppy Emu, or need a second or third unit for your growing computer collection, here’s your opportunity. Thank you for supporting the good work of Samaritan House!

Enter the coupon code GET10GIVE10 during checkout to take advantage of this offer.

The Internal/External Drive Switcher for Apple IIc is once again available in the BMOW Store. The Switcher is a convenience option for Floppy Emu owners with a IIc, and makes everything easier when when emulating a 5.25 inch floppy disk drive. It provides a simple way to select whether the internal floppy drive or external Floppy Emu will appear as 5.25 inch Drive 1, which is the only bootable drive on the IIc. More details are here.

I’m experimenting with methods to limit the inrush current when an SD card is inserted, and beginning to wonder whether my solutions are worse than nothing.

When an SD card is inserted into a board that’s already powered on, a large amount of current will flow briefly, as the card’s internal capacitors are charged through its 3.3V supply pin. This is called inrush current. If the inrush current is too large, it can overtax the main board’s voltage regulator and capacitors, causing the board’s supply voltage to drop temporarily. If the voltage drops far enough, it may cause the board’s microcontroller to do a brownout reset. That’s what happened with early versions of the Floppy Emu. It wasn’t really a problem, because you’ll almost always want to perform a reset anyway after inserting a new card, but it was slightly annoying.

In later versions of the Floppy Emu, I added a 1 uH inductor and 10 uF capacitor for the SD card, as shown in the circuit schematic above. Later the capacitor was changed to a 33 uF tantalum. The purpose of the inductor was to limit the inrush current, preventing the main board’s supply voltage from sagging and causing a brownout. And it worked, mostly, as confirmed by observing the main supply and SD card supply voltages on a scope during card insertion. The exact behavior depended on the brand and type of SD card and the card’s internal circuitry. Some types of cards still caused a brownout reset when hot-inserted, but it was rare.

Revisiting this question again recently, I noticed that the inductor created a new issue that may be worse than the one I was trying to solve. When the SD card is inserted, its 3.3V supply pin doesn’t go cleanly from disconnected to connected. Instead it bounces and wiggles over a period of microseconds to milliseconds, just like the contacts of a mechanical switch. As a result, the inrush current isn’t one single burst, but a series of short on/off current pulses. Because of the presence of the inductor in the circuit, these pulses create voltage spikes on the SD card’s 3.3V supply pin. They’re brief – lasting about 100 ns – but some of the spikes go above 4V. Despite their brevity, I’m wondering if they’re high enough to damage the SD card.

Using an inductor seems to be a pretty standard solution for SD card inrush current, but I’ve never seen any discussion of the voltage oscillation and spikes this can cause for the card’s supply. An alternative is a power management IC with “soft start” behavior, but I’m not interested in adding extra chips in this case. I’m starting to think it may be best to remove the inductor, and connect the card’s 3.3V supply directly to the board’s 3.3V supply. Better to cause a nuisance brownout due to high inrush current, than to risk damaging the card with voltage spikes – and still have brownouts sometimes anyway. Have you ever dealt with this topic? How did you address it?

Version 2 of the Apple IIc Internal/External Drive Switcher is here, and is working nicely. It’s mostly the same as version 1, except for a few tweaks to the piece that goes inside the IIc case. Although the inside fit is still very tight, with this new version it’s a little more forgiving. I also updated the switch labels on the external portion of the drive switcher, with an icon showing parallel arrows for normal mode, and crossed arrows for drive swap mode.

In my previous trials with the drive switcher, I threaded two wires through a gap in the Apple IIc case around the 19-pin disk port. That works, but I’ve concluded it’s easier to thread the wires through the gap around the composite video connector instead, as shown in the photo below. There’s a little bit more wiggle room, and it avoids blocking the faceplate of the male DB-19 connector when the external portion of the drive switcher is plugged in. Threading the wires around the video connector doesn’t cause any blockage problems, and I had no difficulty plugging in the video cable. You could also thread the wires around the DB-15 monitor port, which most people aren’t using anyway.

I think it’s ready! Now I just need to assemble a few of these and get them ready for sale. If you’re interested in helping to beta test the first few units, please let me know.

Oops, I did it again: another 10000 DB-19 connectors fresh from the factory! After helping to resurrect this rare retro-connector from the dead in 2016, and organizing a group of people to share the cost of creating new molds for manufacturing, I had some of the 21st century’s first newly-made DB-19s. The mating connector is found on vintage Apple, Atari, and NeXT computers from the 1980s and 1990s, so having a new source of DB-19s was great news for computer collectors.

But that was two years ago. After manufacturing, the lot of connectors was divided among the members of the group buy, leaving me with “only” a few thousand. Since then I’d used up more than half of my share in assembly of the Floppy Emu disk emulator, and I began to get nervous about the looming need for a re-order. It was such a big challenge the first time finding a Chinese manufacturer for the DB-19s, and the all-email company relationship was tenuous. What if they lost the molds? What if my contact there left the company? What if the company went out of business? Even though I didn’t absolutely need more DB-19 connectors until 2019 or 2020, I decided to lock in my future supply and order more now.

I needn’t have worried, and the transaction went smoothly. With no mold costs to pay this time, the only challenge was meeting the 10000 piece minimum order quantity. I was even able to pay via PayPal, instead of enduring the hassles and weird scrutiny of an international bank wire transfer like I did in 2016.

So now I have a near lifetime supply of DB-19 connectors. Call me strange, but it actually gives me a warm fuzzy feeling. Now to find someplace to store all these boxes…

If you’re using a Floppy Emu disk emulator with an Apple IIc, you’ll want to see this: a switched adapter that can reassign the external 5.25 inch drive as internal, and the internal 5.25 inch drive as external. This little gizmo helps to work around the Apple IIc’s inability to boot from an externally-connected 5.25 inch drive. That shortcoming is a headache for 5.25 inch disk emulators like Floppy Emu. With this internal/external drive switcher, the limitation is now gone!

 
Background

The IIc has an internal built-in 5.25 inch floppy drive. The internal drive appears to the computer as slot 6, drive 1. If you connect an external 5.25 inch floppy drive, it will appear to the computer as slot 6, drive 2. Unfortunately the whole Apple II family is designed to check for a bootable disk in drive 1 only. The computer can boot from drive 1, and then use drive 2 as a secondary disk, but it can’t boot from drive 2. So for the IIc with its built-in drive 1, this means it can never boot from an external 5.25 inch drive.

An important detail: this limitation only applies to the Apple IIc with an external 5.25 inch drive. An external Smartport drive (like Floppy Emu when configured for Smartport hard disk emulation mode) appears to the computer as slot 5, drive 1, and is bootable.

Apple IIc owners who want to boot from an emulated 5.25 inch disk image are in a difficult spot. Until now, their best option has been to remove the top panel from the IIc, disconnect the internal floppy drive, and connect the Floppy Emu to the internal drive connector on the motherboard. This works fine for the Floppy Emu, but it means IIc owners forfeit their ability to use the internal drive.

 
How the Drive Switcher Works

There’s almost no difference between the internal drive connector on the motherboard and the external drive connector at the rear of the Apple IIc. Although they’re different shapes and even have different numbers of pins, they feature the exact same disk IO signals except one: the drive enable signal. To perform this drive switcheroo, the adapter needs to tap into the signals from the motherboard, divert the enable signal externally, and route the external enable signal back inside to the internal drive. This is easily accomplished with some headers and wires and a slide switch, but the tricky part is making it all small enough to fit inside the Apple IIc case.

A slide switch makes the drive remapping optional. At one switch position, the external drive will appear as drive 1 and the internal as drive 2. At the other switch position, the internal drive will appear as drive 1 and the external as drive 2. Now Apple IIc owners can have the best of both options.

 
The Hardware

This is a two-part device: a signal tap that should be installed inside the Apple IIc, and a modified DB19 adapter with a slide switch for the external connection. Two female-female jumper wires are passed through a gap in the case to make the connection between the two parts.

The signal tap portion of the drive switcher looks a little peculiar, and it’s a minor challenge to solder closely-spaced through-hole components to the top and bottom of a PCB like this, but it works. The top is just a standard 20-pin male shrouded header, with a polarizing key like the one used on Apple drive cables. The bottom is a PCB-mounted female version of the same connector – not a very common part, but fortunately Digikey has it. The only other component here is a 2-pin male header for attaching the jumper wires.

Step 1 is to remove the top panel from the Apple IIc (follow the instructions here), and locate the ribbon cable that connects the internal floppy drive to the motherboard.

Disconnect the ribbon cable from the motherboard, and plug the signal tap into the motherboard in its place.

Then plug the ribbon cable into the signal tap. Also connect one end of each jumper wire to one of the signal tap’s male header pins. Here I chose to connect the brown wire to pin 1, and the red wire to pin 2. I’ll need to make the same choice later for the external jumper wire connections.

Before closing the case, it’s important to squish the ribbon cable down into the gap between the signal tap and internal floppy drive bracket. Push it down as far as it will go. This will make it easier to fit the top cover back on later. Notice the difference between the ribbon cable position in this photo as compared to the previous one:

Now it’s time to close the case. First, set the top panel loosely on the IIc, and thread the jumper wires through the opening for the disk connector in the rear of the case.

Then reinstall the top panel. It’s a snug fit, but there’s a large enough gap between the top panel and the rear connectors for the jumper wires to squeeze through. As an alternative, the jumper wires can also be threaded through the opening for the printer port or the video connector. After the top panel is reinstalled, it should look like this:

Connect the jumper wires to the 2-pin male header on the switched DB19 adapter, remembering to use the same color-to-pin mapping as before. Then plug the DB19 adapter into the Apple IIc’s external disk port. It will replace the standard DB19 adapter that’s included with the Floppy Emu.

Finally, connect the Floppy Emu’s 20-pin ribbon cable to the switched DB19 adapter. All done! This Apple IIc can now boot Choplifter and other 5.25 inch disk image favorites from the Floppy Emu, while retaining the internal 5.25 inch floppy drive for secondary needs like disk copying. Or at the flick of a switch, the IIc can be restored to normal operating, with the internal floppy drive configured as the boot drive.

 
Coming Soon

I hope to have the IIc Internal/External Switcher ready for the BMOW store in a month or two. There are still a few wrinkles to iron out before it’s ready. Because it’s such a tight fit inside, I need to get feedback from some other IIc owners to verify the switcher fits their computers too. I also want to revise the PCB a bit, to make the switcher easier to assemble. And I’d like to provide more meaningful labels for the switch positions than simply “A” and “B”. If there were enough space, I’d label the switch positions something like “normal” and “swapped”, but the adapter is so small that there’s only room for 1 or 2 letters at most. Any great suggestions?