The return of PQNG

Much to my surprise, after donating a CPU module (used in PQNG) to Jope / Extend to play around with, he managed to get it running Linux from a CF-card. Pinging local host, is there any more inherent use for any computer system running Linux? ;).. Now, I have no certainty why this boot media didn’t work for me the first time around, but inspired by Jope’s success I decided to give them a second spin.. And what do you know, PQNG booting from a CF!

This time around, what changed was that I had some smaller CF cards and a factory-made IDE-to-CF adapter. The adapter I built myself wasn’t the source of problems (works fine on my desktop PC), so I’m guessing there has to be some kind of low-level differences between CF-cards other than their size. Could also be a newer BIOS on the CPU module. Back in 2008, the cards I tested were all above 1Gb whereas they’ve now been below 256Mb. Out of what I’ve tested so far, the failed ones have been a 256Mb Transcend and a 32Mb Canon. Then again, to contrast this I also have a second 32Mb Canon that works just fine.

The working one

The problematic cards kind of work half-way-there; if you leave the CPU to auto-detect one of these for a minute or two, it’ll eventually see their size correctly (cylinders/heads/sectors) and boot. Running FDISK on DOS, the cards can be partitioned and initialiazed, but not booted from. The CPU simply refuses to see these as system disks although MBR is ok and command.com exists. No idea if these cards would work using Linux.

Anyway, coming back to PQNG.. As there is now a replacement boot medium for the floppy, it looks like this bit of DIY is back in effect! As Grue / Beyond Force was kind enough to donate a bunch of small CF cards (≤128Mb) for initial testing, I figured I’ll build him a PQNG in return of favor. Enter PQNG #3 :)

For this “next generation model”, I initially designed the PSU to be used with a recycled laptop wall wart. But when commencing with the actual build, I decided to test making the choice of wall wart configurable by adding a couple of jumpers to the power input/output rails.  The idea was to allow the unit to be used with a +12VDC wall wart as well, leaving Grue with a bit more choices in case of part failure. Too bad that I failed to think things all the way through so in the end, because of the model/type of DC/DC converters I chose, the extra configuration features turned out pretty pointless..

Close-up of the PSU section.

Looking at the picture above, the configuration jumper near the green power connector allows the +5V and +12V DC/DC converters to be fed either separately (sharing a common ground) or from the same supply. This enables using both single and dual positive rail wall warts. The other two jumpers allow bypassing the +12V DC/DC converter altogether, so that the unit can be fed using a +12V wall wart.

Additionally, both posivite input rails are protected by self-resetting thermal fuses. If the unit starts drawing too much current, these will cut off the external power supply. The conductive state is restored after power is kept off for around 30-60 seconds. I also added a dimming control trimmer for the display backlight DC/AC inverter on the PSU board.

And the pointless part about the PSU? Well, the thing I forgot about was that the DC/DC converters have a minimum start-up voltage of +16VDC (specced input range is 18-36VDC). Once started, they do run at lower voltages though (down to around +9VDC). But still, if you’re unable to supply the start-up voltage..

CF makes it so much more compact.

One improvement waiting to be tackled is making time adjustments. Currently, the only option for changing between summer/winter times is to attach a PS/2 keyboard and adjust the BIOS clock on the CPU card. Not too handy and standalone, so to say. With a bit of hardware and software changes, something like “hour +1” and “minute +1” functionality could be implemented. Buttons could be easily interfaced through the parallel port and so forth. Come to think of it, installing a couple of buttons more a game mode could be added too :)

Rear side of the assembled unit. PS/2 cable "professionally" attached with cable ties.

Currently, as I have no source for recycled CF-to-IDE adapters, using CF cards also means that the device is not 100% recycled (like it was with the floppy drive). But still, CFs do make the unit so much more easy to construct (and it draws less power too) that I think this “drop” in recycling percentage is more than allowed for the time being.

Nonetheless, if you happen to have a box full of small CFs and CF-to-IDE adapters to donate, maybe we could arrange a trade of sorts ;)

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