I have an Onn Surf 8 (One of the surprisingly-not-that-shitty ultra-cheap Walmart tablets) that my research group bought a couple of to use as Android dev testbeds. I’ve been occasionally using it as a normal tablet since I have it around, and have been consistently irritated by the collection of bloatware it comes with…. so I decided to hack it. To tl;dr this whole thing, ignore the collection of typically scammy Android dev forum and blogspam crud, and use the open-source mtkclient for your MediaTek Android device hackin’ needs.
I’ve wanted a hard-copy terminal for a while – both to play with and to use for explaining why serial works the way it does, but they tend to be expensive. Most of the common hard-copy terminals also aren’t really convenient objects to own: loud desk-sized machines (Teletype 33 family, most DECWriters), additionally clockwork nightmares (IBM 2741, earlier Teletype devices), which speak ridiculous protocols (…ditto). This only leaves a handful of reasonable options, the most common of which are portables like TI Silent 700s and DEC LA12s, or one of the dasiywheel-printer based terminals (which are often non-period-correct things like a WheelWriter with a modern serial interface card in it).
So, of course, I’ve been idly keeping an eye out for a deal on one on the auction sites, and mid-October last year I got lucky: I scored a TI Silent 700 Mod. 745 for $34.00+S&H (about $47 all in) from a Shopgoodwill auction, and got it working.
An old friend of mine was moving cross-country and got in touch about taking “Some of his old computers” a while ago. I of course agreed, and it turned out to be quite a growth event for my hoard. There will be several posts about machines that arrived in this process as I get to them.
The list of things to be re-homed included “an Apollo” which I was hoping was a pre-acquision DN-something or a HP 300/400 series because I’ve had a long fascination with Domain/OS. What showed up is… not that. This is a later HP Apollo 9000/735 PA-RISC workstation, ca. 1992, which is easily the most exotic piece of hardware that transaction made me steward of. The OS options are HP-UX 7-10.20, a few BSDs, or a second-class NextStep 3.3 port; I’ll probably go with HP-UX10.2. It came with the requisite HP-HIL keyboard and mouse (thank goodness) and a DEC branded 5xBNC to VGA cable.
This thing was serious rarefied-air hardware when it was new: PA-7100 99 MHz processor, 208 MB of RAM in 12 obscene proprietary 16MB RAM modules + 16 soldered to the processor board, a HP CRX-24Z video board, a full-height SCSI HDD, and an AUI Ethernet daughter card. Probably in the ballpark of $60,000 new. It is also built like a piece of high-end industrial equipment, with big sheet-metal frames with handles that pull out of the back of the system for every major component.
My first attempt to power it resulted in …a feeble blink of the power light. That suggested to me that the PSU was bad, probably due to defunct electrolytic capacitors. So, in standard “old electronics troubleshooting” fashion, I pulled the PSU, tore it down, read labels off the most suspicious capacitors, and ordered replacements. The HP Museum folk also suggest the AC line filter module is a time bomb on all of these, so since it’s still made, I grabbed one of those too.
List with Mouser links, since they were the vendor with everything I needed in-stock: 8x 2200uF 25V, 12.5mmD 40mmH, 5mm lead spacing , Nichicon UPJ1E222MHD firstname.lastname@example.org 1x 220uF 35v, 10mmD, 20mmH, 7mm lead spacing, Nichicon UPM1V221MPD1TA 1@$0.72 1x 1x 22uF, 25V, 5mmD, 12mmH: Nichicon UPS1E220MDD1TA email@example.com 1x 12uF, 35v, 5mmD, 10mmH, Panasonic EEA-FC1V120B 1@$0.39 1x AC Power Entry Module, Schaffner FN9222R-10-06, 1@$6.50 I also ordered a couple 470uF 25V, 10mmD, 20mmH, 5mm lead spacing caps, but ended up not installing them because there was no sign of damage and they were hard to get a good angle on.
I passed on dealing with a couple smaller electrolytics with no signs of damage, and also two gigantic 2x 1200uF, 250v, 35mmD, 47mmH, 10mm lead spacing input caps that cost $7.50 a piece, since they looked both fine and like a fight to get out without damaging the PCB. One of these days I really need to invest in a proper pump-driven desoldering gun to make this kind of task safer and easier.
I of course picked up an extra 1-2 of each since it was noise over paying for shipping, and it’s a good thing because I dropped one of the new 220uF/35V parts and it instantly disappeared forever, presumably to wherever my cat has been hiding toys recently. The new input filter is slightly longer than the original and required a bit of creative terminal bending to fit around the caps, but it made it back into the case. After the recap, it powered right up, and on a second try after giving the hard disc a gentle thump to unstick the heads from park, everything spun right up.
Full Status LEDs. 8,6,3,1 = “Autoselection Failure to Find Boot Device”
It booted to status LEDs at that point, and shows “8,6,3,1” which according to the service manual indicates “Autoselection Failure to Find Boot Device” – probably meaning the HDD is dead and/or wiped. The appropriate HP/UX media is easy enough to find. Unfortunately, the monitor on my basement bench doesn’t seem to want to sync with the presumed 1280×1024@72Hz Sync-on-Green coming out of the video card, so I’m stuck for now until I can find a workaround. There is a 4th BNC labeled “Stereo” that might somehow be useful for sync? Or I need a scan converter/sync stripper gadget? … further research required.
I impulse bought a 5 pack of tiny stepper motors off Amazon for $3 to satisfy my curiosity. A colleague showed them to me and asked if I knew anything about them and …I didn’t, but they were too cheap and interesting not to try.
I couldn’t find any documentation on the internet from the identifying marks, so I burnt an afternoon figuring them out, and I’m posing my notes in case anyone else wants to make use of them.
The labeling on the motor itself is “SRG0808 003PLK5” which doesn’t turn up anything useful in a quick search, and the bag they came in is labeled “Fashion Worlds stepper motor 9496 x5” which is also not something googlable.
The motor comes attached to a flat flex cable with various adhesive pads built in, a boardlet, and a connector at one end. The output shaft is set in a brass gear roughly 2.75mm diameter with 12 involute profile teeth, about 3mm long – I don’t know small gears well enough to infer a ton from this, but it does seem like there is a lot of compatible gearing on the market.
Test setup for one of these steppers
To get around the lack of documentation, I probed one out with a DMM then built a test rig out of a dual L9110S H-Bridge board and a little STM32F103 dev board with the AccelStepper Arduino library to figure out the details.
They appear to be 20 steps per revolution motors, though they seem to work noticeably better with a half-step drive pattern. They work nicely at 3.3V, but get a little hotter than I’m comfortable with if energized for an extended period of time; I also tried 5V and it seems to tolerate that fine as well, gain a noticeable amount of extra torque, and get appreciably louder.
I don’t have the tools around to easily test the effective torque, but was way more than I expected based on my experiences with other small hobby motors. In my little taped-to-the-table test setup (pictured), if I jammed a fingernail into the rotor when it was already at speed at around at about 1000 steps/s on a 5V supply, the motor and/or nail deflected rather than missing steps.
If you look at the motor with the output shaft facing away from you and label the four pads A,B,C,D, the phases are A-D and B-C with about 9Ω across each phase.
FPC Connector Pinout
If you look at the attached flat flex cable with the end pointed toward you, it has 7 contacts. For reference, let’s refer to them numbered 1-7 left to right. The ribbon itself is 4mm wide, and the contacts appear to be 0.5mm pitch, so it would probably mate with any of the various “7Pin 0.5mm Pitch FFC FPC” connectors floating around on the market for cheap if you wanted to spin a driver board for it that used the included cable.
The last 4 cable pins correspond to the motor terminals 4-D, 5-C, 6-B, 7-A… but for experimentation it’s easier to just solder leads directly to the motor pads. I used two pairs out of some old stranded CAT5, visible in the top picture.
IR Reflective Object Sensor Breakout
There is a bonus component on a little arc-shaped boardlet built into the flat flex. It appears to be some manner of reflective infrared optical sensor, which I assume was used to establish a home position in whatever these were designed for use in – frankly since it has convenient mounting holes and wiring it would be pretty nice to use the same way in most applications I would want one of these in.
The first three ribbon pins are attached to this part, and none of these pins are shared with the motor itself. For discussion, let’s number the pins 1,2 left to right on the side toward the flex cable, and 3,4 right to left along the other in typical IC fashion. The pins are broken out Part 1 = Flex 1, Part 2 = Flex 2, Part 3 = also Flex 1, Part 4 = Flex 3.
Two of the pins (+ on 2, – on 3) appear to be a diode with a 1V forward voltage, and after I thought about it and checked with a camera with a bad IR filter, it is an infrared LED. The other pair seem to be a phototransistor or similar; it reads about 1.5MΩ from pin 4 to pin 1 in darkness and 1KΩ across the same with an IR LED pointed at it.
I’m not sure what I’m going to do with these, but they seem promising for small motion systems, especially since (if I bought bulk packs of each from China) you could get the motor and pair of H-bridges to drive it for under a dollar. Hopefully I’ll run into something to play with them in and/or my reversing work will enable someone else’s cool project.
Yesterday I pulled my ThinkPad 560E out, dd’d a floppinux on to a real floppy, booted it up and… it traps on an invalid opcode as soon as it tries to load init.
A little thinking made me realize that the way they were building their busybox binary was contaminating it with libraries from the system they were building on (which was apparently i686), so despite all their “will work on a 486 or later” option selections, the images they produced only work on i686 or later boxes.
I opened an issue then got obsessed and decided to fix it myself, and … you can read the details in my followup to the issue.
The magic lazy out for this kind of thing now is the pre-built musl based cross toolchains provided by https://musl.cc/
I made a couple other suggestions (about using musl, about configuring the kernel for xz and using it for the initrd, etc.) while I was hacking, because putting together little cross-compiled Linuxes is something I used to know what I was doing with. It did take a couple hours to spin back up, there are always picky cross-environment things to remember, and things have changed, mostly for the easier.
I’ve posted a copy of my generated i486-clean image. (Subsequently swapped out for a rebuild with slightly more useful busybox and kernel options, but only about 450k free)
Not that I’m a frequent IRC user for the last several years, but since the freenode implosion seems to have settled out as a real thing, I’ve gone ahead and registered myself as pappp on oftc and libera.chat where the … Continue reading →
Printed and painted Kestrel and Lightning models on a PowerBook 5,4
I had my regularly-scheduled itch to play Escape Velocity or one of its successors and/or clones the other week, and decided to play the real thing this time since I did a lap on Endless Sky not too long ago, and NAEV still doesn’t quite grab me.
I’m now most of the way through a game of EV (under emulation in Basilisk II), and …impulse bought a cheap 2004 15″ Aluminum PowerBook G4 (a 5,4) off the internet after a crash ate a save file. I have good coverage of Apple 1984-1994 in my collection (in the form of bulky desktops with CRTs), and x86 OS X is pretty easy to run in a VM, but I have a hole in the late PPC era. That machine will hopefully eventually also get its own post as I finish fixing it up, it’s not in perfect condition but it auctioned below prevailing when I was looking, and seems to be acceptable.
While I was looking into the player communities (…because it’s become very hard to set up a working install of EV Nova recently, and I can’t find a backup of my registered copy) I discovered that a couple months ago some wonderful person (slurked on thingiverse/quarmus on reddit) made and shared 3D models of the Kestrel and Lightning ships from the original EV.
…So the little Mac-user child of the 90s in me promptly headed down to the basement to print a Kestrel and a pair of Lightnings.
I gave them a quick sand to take the worst print artifacts off and sprayed them down with a couple coats of gray Krylon Fusion, which gave a decent base coat. I needed to do a little (bad) detail painting on the Lightnings, and the acrylics I have around didn’t stick well to the spraypaint, so I dug out my decades-old Testor model enamel set. Eventually they were shaken and stirred enough to get the job done; in another post post, an absurd over-engineered shaker that didn’t really solve the problem.
EV is still one of my favorite games, though I think Endless Sky’s implementation of the formula is actually significantly better for a modern player without the memories, especially now that Ambrosia is defunct and the hacks around registering Nova seem to not be working.
As I continue my electronics part organization spree, I was looking for …something… reasonable for through-hole resistor storage. Resistors are a problem because there are a lot of values, once mixed they’re possible-but-irritating to distinguish, and strips of resistors are awkwardly shaped.
There are some special-purpose drawers, most of which aren’t very flexible (configured to hold exactly the E12 series, or with slots too small for the 4″ strips a lot of cheap resistors come in, or…), and many of which are enormous 3D printing projects in their own right that I didn’t feel like dealing with. There are some systems with small or card-catalog style drawers, but I don’t stock large enough quantities of resistors to invest that kind of money/space, and don’t plan to. I also looked at variations on schemes using card holding binder pages, since I really like the cheap SMT binders (link is the ones Adafruit stocks, mine are all the ubiquitous brown ones with gold-debossed Chinese text because I’m cheap), but after I bought a pack of the appropriate business card slot binder sheets I realized I’d underestimated my size requirements.
I added some E24 values (like 51x and 75x) that I had stocks of from one purchase or another, and a few other odd labels that I happen to have stocks of. The added labels are missing the cute little colored resistor images because I’m not sure how they were generated and it wasn’t urgent enough to spend a ton of time on – I just put the value and the band numbers on those.
I did cheap out on basically every part; I used 2mil 3×4″ baggies instead of the nice 6mil ones, and I used AmazonBasics 1 x 2-5/8 Inch labels that list themselves as compatible with Avery 5160 labels. Both of those may eventually prove to be a mistake, but for now they work and feel fine.
One thing I am looking to improve upon, I currently have them stored in an old Kroger deli meat tub, which is OK but not ideal. I don’t think I can find something that will hold them reliably and still clear the 3″ height of the drawers I’ve been packing a lot of my component assortments into, so I’m probably looking for something that will close, possibly a large-ish 3×5 card organizer.