Miscellaneous electrical and cyber engineering notes.

Notes From The Nerd Cave

Miscellaneous Electrical and Cyber Engineering Notes

Themeless other than potentially useful information which seems rare or absent on the Internet.

27 February 2023:  Power Macintosh 7200/90 internal edge card connector images added.

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Efficiently store components of all kinds in a single set of six decade range containers.

Superb quality hand soldering using organic flux.

Storage volume target mode is easy in any SCSI equipped Classic Macintosh.

Enable Silicon Image Sil3112 equipped SATA cards in Classic or OS 10 PCI based Macs.

Replace corrosion time bomb clock batteries with far safer super capacitors.

What is the function of the Power Macintosh 7200/90's internal 22 pin edge card connector?

Modify common motion detector modules to reliably provide long on times.  (Not yet posted.)

Copyright notice.

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Efficiently store components of all kinds in a single set of six decade range containers.

Updated 23 February 2023:  Tiny refinement, but images still not yet added.

This is for hardware engineers who maintain stocks of small components for prototype or small quantity circuit fabrication.

We utilize a large range of numerous type of circuit components, all of which must be organized into containers for ready access or restocking.  If this is done in the most obvious manner, with a separate container for every component of every kind, the number of containers required is mammoth, rendering that method entirely impractical.  There's a far better way:

It's trivially easy to visually discern different component types irrespective of physical size - resistors, capacitors, inductors, zener diodes, fuses, crystals, ICs, varistors, and several other component types are immediately distinguishable on sight.  So since they differ in appearance, whether surface mount or leaded type, they can share a container yet cause no identification problems.

In addition, components of a specific type but different value are almost always easy to visually distinguish from each other if their values differ by six orders of magnitude.  Resistors are an exception but they're almost universally well marked so their actual values are easy to read.

This means that all these components may be stored in a single array of 72 containers, yet any component of any kind or value can be almost instantly retrieved or restocked.  Here's how to configure it:

Acquire cabinets which can be configured to provide 12 columns by 6 rows of containers.  Four column by six row container cabinets are common, three of which provide the necessary 12 x 6 matrix.  This provides 12 columns to delineate every standard 20% component value (1.0, 1.2, 1.5, 1.8, 2.2, 2.7, 3.3, 3.9, 4.7, 5.6, 6.8, and 8.2), and six rows to delineate six decade ranges (from unity through 10 M, or 10 µ to unity for example).  The decade ranges don't need to be bounded, but for most engineers 1 f (10 -15) through 100 G (100 x 109) covers almost every discrete component value available.

The top left container holds components with values from 1.0 to but not including 1.2 with p, µ, none, or M suffixes.  The next container right holds values from 1.2 to but not including 1.5 with p, µ, none, or M suffixes.  The container just below the top left holds values from 10 times 1.0 to but not including 1.2 with p, µ, none, or M suffixes.

So all containers hold values with six decades of difference.  For example the top left container holds 1 Ω and 1 MΩ resistors and 1 pF, 1 µF, and 1 F capacitors (the last a super capacitor), and other components whose values similarly align.  This means the container holds a broad mix of components of any kind any of which may have p, µ, none, or M suffixes.  Such differences are utterly easy to discern by eye in almost all cases, except that some resistors might require reading of their body markings.  All others are visually obvious - 1 µF capacitors of any kind are physically larger than 1 pF capacitors for example.

Delineation is by specified values with zero hedging.  So for example a small bag of resistors might have a specified value of 4.699 KΩ, and include some samples with actual values of 4.700 KΩ or a bit higher.  But they are placed in the 3.9 K container, not the 4.7 K container.  Delineation must remain absolutely strict to avoid chaos.

Images of my containers should be shown below soon.  They contain any small component of any kind which has a primary value.  Zener diodes by zener voltage, precision voltage reference ICs by reference voltage, fuses or circuit breakers by breaking current, variable resistors by maximum resistance, crystals by frequency, lamps by operating voltage, or anything else with a primary value for which the component is selected for use in a circuit, with all other parameters secondary.

An option is an array of 144 containers in a 24 x 6 matrix to delineate every standard 10% component value.  However that delineation is too fine for the vast majority of individual engineers - a 72 container array is more practical for us in my estimation.

This system works exceptionally well!  Instinct is to establish container arrays for resistors, separate container arrays for capacitors, other arrays for inductors, more arrays for zener diodes, more for fuses, and many more.  And a separate container for each individual value covering the entire range of the component (no six decade rotation).  And separate arrays of containers for every component type, such as one for tantalum capacitors, another for MLC surface mount capacitors, another for electrolytic capacitors, and another three arrays for leaded versions for all those capacitors.  That level of delineation is necessary in production environments, but is so utterly impractical for nerd cave environments that it's almost never actually achieved or maintained.  So chaos ensues, and very often engineers order new components because, although they're quite sure they already have them somewhere in their stock chaos, they can't find them.  And they rarely restock small components because they can't reasonably find a proper container to store them within.  So they're often simply discarded.  The overt waste is bad enough, but additional serious problems are long delays to component availability, which delays projects, and wasteful new order management time.

I created my first consolidated container system a bit over 40 years ago and am still happily using the same physical containers in their original matrix with original labels today.  I retrieve very nearly every small component I need almost instantly with no delay at all.  Sometimes I must check a value, but that's quite rare (maybe a few times a year) and in most cases the exercise merely confirms my initial judgment, though for certain components (usually zener diodes), when markings aren't clear I must measure to discern the precise value within the 20% container range.

Skeptical?  Well, I get it - the notion of mixing components so extensively seems guaranteed to create chaos.  But in fact the reverse occurs - this container array delineation method renders every component perfectly easy to store and extremely easy to retrieve - it works.  And it's immensely more space and time efficient than any other system - space efficient for the obvious reason, and time efficient because every component's stored or retrieved from a single array of containers right at your finger tips - there's no need to walk to a remote location to store or retrieve components in distant containers.

Try it - you'll see - it works!

Superb quality hand soldering using organic flux.

Posted 22 February 2023.

Consider water soluble organic flux instead of rosin flux.  It renders truly perfect joints and enables easy fine pitch IC soldering by simply swiping each row of pins with a ball of molten solder on your soldering iron tip.  The organic flux keeps the solder completely clean so it retains full surface tension like pure mercury, so the molten ball jumps cleanly from one pin to another leaving (usually) no shorts.  But for the last three or four pins a jump off platform is needed, such as copper braid or just a thin strip of solid copper or other solder compliant metal, or adjacent empty feed through holes often suffice.  Organic flux is available as a liquid which may be applied generously with a small art brush.  Fully immerse the working area - use plenty of it.  And use either solid solder or solder cored with the same organic flux (such as Kester 331 solder) - don't use rosin core solder.

It washes off completely with mere hot water, though I use detergent and a toothbrush as well to insure any other contaminants are also removed.  You must wash it off reasonably promptly - the flux is both corrosive and conductive so it must be completely removed.  You can work for about 90 minutes but then should wash since longer linger times result in metal surface tarnish (not serious but not as gorgeous).  You must clean your work area and all tools as well since any residue would cause corrosion and conduction trouble for anything which contacts them.

The work area cleaning overhead is a bit inconvenient, but I use organic flux for all significant soldering work because it's so superbly easy to work with, enables ordinary soldering irons to solder fine pitch easily, and the results are perfect mirror finish joints which are utterly solid and reliable.

It's available from the usual solder vendors - Kester's 2331 flux is described here for example.  AimSolder.com calls it OAJ flux.  You'll need the liquid even if you acquire organic core solder because that solder alone delivers far too little fluid for any work in my experience, especially fine pitch work.  (I doubt it was actually intended to be used alone in most cases.)

It's cheap.  And in my estimation once you experience it you'll never solder circuit boards with rosin flux again.

Storage volume target mode via SCSI ports in any Classic Macintosh OS.

23 February 2023:  Modest addition and refinements.

Most well informed Mac OS 10 and higher cyber system users are familiar with storage volume target mode.  It's invoked by pressing the 'Command' and 'T' keys simultaneously immediately after power is turned on, then holding them down until a FireWire symbol appears on a display.  The system's internal volumes may then be accessed by another system by simply connecting the two systems with a FireWire cable.  The volumes in the system in target mode should mount automatically on the desktop of the second system, where they should be fully accessible in the normal manner.  Such access can be useful in a variety of situations, including bypassing file privilege restrictions which exist on the target system's volumes when booted normally.

This can also be accomplished in SCSI based classic Mac systems, most of which run Mac OS 6 through 9, in a similar manner, but by interrupting the target system instead of a 'Command' and 'T' mode boot, and using SCSI cables instead of a FireWire cable.  It's reasonably easy:  Interrupt the target system by pressing an interrupt button or causing a system crash.  (Currently I don't know of a software means to invoke an interrupt for systems which have no interrupt button, but I suspect one might exist.)  Connect its external SCSI port to the external SCSI port of the second system.  Then simply boot the second system, which should mount the target system's volumes on its desktop, where they should be fully accessible in the normal manner.

A means to interconnect the external SCSI connectors is required.  Two DB-15 to 50 pin Centronics cables and one male to male Centronics adapter might be the most common solution, but any combination of cables and adapters which enable mating of the two external SCSI ports with sufficient signal quality should be functional.

My sense is that no special sequence of operations is required, but the safest sequence might be as described above.

I suspect this method will successfully share SATA devices as well via eSATA ports, eliminating SCSI cable awkwardness, if both systems are equipped with Mac compatible eSATA PCI cards as described below.  I don't know whether the SCSI devices would be mounted as well however, but hope to explore these elements by about Summer 2023.

Enable Silicon Image Sil3112 equipped SATA cards in Classic or OS 10 PCI based Macs.

All credit to "dosdude1".

Details, initial test results, and corrections added 23 February 2023.

SATA Connectivity is provided by a variety of PCI cards but most or perhaps all aren't natively compatible with Macintosh systems.  However the firmware of cards with Silicon Image SATALink Sil3112 bridge ICs may be revised to render them reliably functional evidently in both Classic and OS 10 PCI based Macs.  Once accomplished SATA connected storage, including SSD's, may then be utilized.

This is discussed here and here (and their previous pages, but the linked pages provide the latest information and files as of February 2023.)  The compatible firmware may be installed into a SATA card as it resides in a PCI slot in a Macintosh.  No hardware modification is necessary.  SATA volumes should then mount normally and evidently can be used as boot volumes as well.

I successfully installed this firmware into my lone Sil3112ACT144 equipped SATA PCI card, which utilizes an AM29F010 prom, in my Power Macintosh 9500/120 (with a 445 MHz G3 PowerPC processor card) running OS 9.1 with utter ease - the application is quite straightforward and elegant.  And an attached HFS+ SSD volume seems to operate properly and is able to boot the system.  However I've performed only minimal superficial tests thus far.

Other bridge ICs, such as the Silicon Image Sil3512ECTU128 or HighPoint HPT372NLF, aren't pin compatible with the Sil3112ACT144, so an IC swap would render such cards completely dysfunctional in any environment.

As of 21 February 2023 the files, courtesy of "dosdude1's" great work and reporting at 68KMLA.org, are:

1s2 Patched Compressed ROM
SeriTek 1s2 Flasher 5.1.3
LZSS FCode New

Replace corrosion time bomb clock batteries with far safer super capacitors.

Diode part number correction and minor refinements 23 February 2023.

Separate personal computer clock batteries are often devastatingly destructive time bombs.  They can be replaced with super capacitors which are far less likely to leak and presumably cause far less damage if they do.  (I've never experienced a leak failure of a super capacitor so I can't be certain how much damage would result, but feel confident it would be far less than battery leak damage.)

A super capacitor won't maintain the system clock (RTC, Real Time Clock) for nearly as long as a battery, but super capacitor values of about 2 Farads seem sufficient to maintain the clock for at least a month, which is more than sufficient in most circumstances.  In my view that's a clearly preferably trade for ridding the system of a devastating internal corrosion time bomb.

You'll need a 5.5 Vdc or higher rated super capacitor, a low leakage signal diode such as an ordinary 1N4152, and a very roughly 50 Ω to 100 Ω resistor.  The diode and resistor provide very low stress charge current for the super capacitor and prevent discharge through this path when the computer is shut down.

Remove the battery and its holder, the later a desoldering task.  Then solder the super capacitor to the circuit board pads vacated by the battery holder, insuring proper polarity.  Then solder the diode and resister in a series connection from a nearby + 5 V power location (such pads are usually quite close) to the positive pad of the super capacitor, with the cathode of the diode oriented toward the super capacitor so current can flow from the + 5 Vdc source into the super capacitor, but not out.

An option is to remove the battery but retain the battery holder, then solder the super capacitor to its terminals.  However some battery terminals may not reasonable accept solder.  (And since the super capacitor is a very long life component I consider the battery holder as useless.)

Super capacitors are low in cost and readily available from multiple distributors such as AliExpress.com.

Modern portable devices usually utilize their internal user inaccessible whole system battery to power their clock as well and thus have no clock battery to replace.  But line powered computers or portable devices with user removable main batteries usually have an internal clock battery which is a wicked corrosion time bomb, and thus a candidate for a super capacitor replacement.  I replace them in all computers I value because careful though we all try to be, perfectly disciplined maintenance of internal clock batteries is far more a nice fantasy than reality.

What is the function of the Power Macintosh 7200/90's internal 22 pin edge card connector?

27 February 2023:  Edge card connector images added.

The Power Macintosh 7200/90 contains an internal 22 pin edge card connector on the main logic board just two or three centimeters forward of the external display port.  I believe it's normally empty.  Please advise if you know anything about the function of this connector.  (Click the images for a full size rendition.)


Beyond simple curiosity, I need this information for troubleshooting purposes because my 7200/90 system's native display port isn't functional.  This system is otherwise pristine clean and in excellent, fully functional condition, including replacement of all MLB electrolytic capacitors with tantalum capacitors.  I vaguely think the display was healthy before I began my restoration work but am not certain.

There's also a crystal a few more centimeters forward of the display port, near the processor.  It might be Y4, Y7, or Y12 and is labeled 0103T5H.  It might be a 25 MHz crystal but currently I'm not certain.  Mine seems either dead or set to an off mode by the system.  If dead, such as from cleaning rigors, it might be the cause of my display circuit's failure.  I'd be grateful for any information about that crystal and its possible relationship to the display circuits as well.

More subjects later...

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