So, this month I tried my hand at doing some improvements to the PETpix project as part of the Retrochallenge Winter Warmup. My intent was to do a board layout for PETpix and to have a few of them made up. I didn’t quite reach this mark, but I was happy with some progress I made with improving the iPhone app I used to transfer PETSCII images over to the pet.
Basically, I had made an iOS app which captures an image, converts it to the closest-match PETSCII image, and sends the converted image via audio from the iPhone’s audio jack to a custom board on the PET side. The speed, however was quite slow – over 10 seconds to send a single image over the wire, and a couple of seconds to do the PETSCII conversion.
With some nights of hacking away at it I was able to optimize the code and get the PETSCII conversion down to about .25 seconds, and the image transfer down to about half a second.
This was accomplished by using a different method of transferring data via audio. Before, I was using a frequency encoding technique, much like that used when saving data to a cassette – one frequency for a 1 bit, and another for a 0.
But after a bit of consideration I found that it was possible to just directly convert bits in a serial waveform to levels in an audio waveform. In the last couple of days I was able to reliably send data from the iPhone’s audio jack at a 19.2 kbps rate and read it over a serial port. This required a comparator to square up the output waveform, and an RS232 level converter. I’ll post more details on this soon.
So, in conclusion for the Winter Warmup, I wish I had had some more time this month to work on this. It was a particularly busy month with regular work, and there just wasn’t a lot to spare after the other obligations were completed. But I’m happy to have sped up the conversion/transmission process, and this should enable realtime (albeit 2 fps or so) video display, using an iPhone camera, and displaying with PETSCII on a PET! Hope to get the full chain working within the next week or so.
This was a fun event and will definitely be involved in the full Retrochallenge!
Made some videos of PETpix in its full PETSCIIfied glory. Check them out on the PETpix page.
Wanted to let you know about a new project I’m calling PETpix. It’s a userport add-on for a commodore which lets you play PETSCII formatted video. There are some preliminary processing steps which need to be done on a modern computer to get the video into the right format, but you can convert/play any type of video (AVI, MOV, etc) in beautiful PETSCII. I’ll be posting some videos and more information about this gadget shortly. As soon as I get the chance to do a board layout, the PETpix will be available as a kit to use on your own commodore. Watch for more on this soon..
When collecting old computers, one issue that comes up from time to time is that you’re missing the one piece that you need to get the machine working. Or you have the piece and it’s beyond your ability to repair.
Keyboards are often the culprit. I’ve gotten a few machines with keyboards where the foam pads under the keys had deteriorated enough to prevent the key presses from registering. There are ways to restore the keyboards by getting new foam and laboriously cutting new pads for the keys, but sometimes you just want to get to it and play with your old computer without spending weeks shaving pieces of foam.
PS/2 keyboards are in plentiful supply and are fairly simple to interface with a micro controller. Often with a bit of work they can be adapted to work with a variety of old machines.
I recently saw a post on the Vintage Computer Forum from a guy in Vancouver who needed a keyboard adapter to use a PS/2 keyboard with a Fujitsu FM77AV40SX that was missing its original keyboard. I was interested in helping out, since I had some experience building a PS/2 to ASCII converter to use a digital group computer.
But one wrinkle was that I did not have access to the computer, so debugging any adapter would be a bit of a challenge.
Coming up is an account of an exercise in remote debugging using a protoboard with an AVR microcontroller, equipped with a serial port bootloader. It’s a thrill a minute I tell ya.
Hopefully this will help out collectors of Fujitsu computers who are missing their keyboards! Stay tuned for more..
Wanted to let you know about a new device for your Commodore PET: The PETvet!
Basically, the PETvet replaces all of the RAM and ROM in your PET using a single SRAM chip. Different ROM images are stored in the flash memory of an Atmel microcontroller, which pre-loads the ROM contents into the right place in memory before the CPU starts running.
You can also use the PETvet to view the memory contents of a running PET by dumping the contents over a serial port. This can be useful when debugging an ailing PET motherboard. It can also be used as a basic terminal output for a PET by viewing the contents of video RAM.
The PETvet is in the final stages of testing right now and will soon be available here as a kit or as a fully assembled unit. More details to come.
Finished another firmware update, this one allows you to use long file names when saving files on the PETdisk. So now you can save something like
and it will work. Yippee!
Download the update on the PETdisk Technical page.
That’s right, those fine podcasters of the Retrocomputing Roundtable(subscribe here) mentioned the PETdisk in their latest episode (show 16)! I am a fan of this podcast and of the individual podcasts of the hosts (Retrobits, 1mhz and the Classic Computing podcast) so it was a thrill to hear them talk about this little project on the interwebs. Thanks guys!