155 lines
7.2 KiB
Plaintext
155 lines
7.2 KiB
Plaintext
The most significant challenge in this project is easily the Dreamcast serial
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connector.
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As a comparison, Dreamcast "AV connectors" can be purchased at a unit price of
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roughly $1.70 USD on Ebay or $1.00 USD on Aliexpress. These are quality
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connectors that appear to use a copper alloy for the conductive pins. The
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dimensions and fit appear to be reasonably perfect, and the mounting style is
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suitable for direct soldering to a 2.0mm thick PCB.
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In contrast, Dreamcast "Serial connectors" only exist either as Sega-original
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parts (and therefore not available in consistent bulk quantities), or in the
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"Dreamcast SD adapter".
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I asked many sellers whether they were able to provide the raw connector (not
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yet soldered to a printed circuit board), and in all cases the vendors informed
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me this was not available. The best-advertised price for a complete "Dreamcast
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SD adapter" appears to be about $7.00 USD.
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The Dreamcast serial connector from the "Dreamcast SD" product is also vastly
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inferior to the Dreamcast "AV connectors", despite being a very similar
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connector differing only in width and pin count.
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At least the following issues exist:
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- the outer dimensions of the Dreamcast SD serial connector are too small
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- the retaining holes that are intended to "latch" with the female connector's
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detents are slightly misaligned
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- the injection molding is significantly lower quality compared to the Dreamcast
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AV connector
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- the conductive pins appear to be a plated aluminum alloy, a downgrade from the
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AV connector's copper alloy
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Despite this, $7.00 USD is still a decent price. I then investigated the
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viability of salvaging the Dreamcast serial connectors. However, I was
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discouraged when I found desoldering to be too difficult. The issue is a
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combination of:
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- the pads on the Dreamcast SD PCB are too narrow (both as a general statement,
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and as it applies to desoldering specifically), which increases the
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difficultly of applying copper braid
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- a high-temperature solder was used--this means excessive heat is required,
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which risks deforming the injection-molded plastic
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I found the best approach to salvaging "Dreamcast SD connectors" is to instead
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cut the PCB, first separating the Dreamcast serial connector from the bulk of
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the PCB, then cut the PCB between each conductive pin. The pins can then be
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removed individually, which makes cleaning the pin much easier.
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However, all of this considered, I felt that surely it would be easier to just
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make a completely new connector, rather than undertake this scavenging
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process. This would have an additional advantage that already-cleaned connectors
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could be installed at a PCB-assembly factory, no doubt more cleanly, quickly,
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and cheaply than I can do myself.
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My original idea was to attempt to directly copy the design of the Dreamcast SD
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adapter's Dreamcast serial connector verbatim.
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In my discussions with rapid prototyping factories, the most immediate issue is
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the outer metal shield. This metal shield must fit between a small gap (roughly
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≤0.5mm) inside the female connector. At that size, it effectively means the only
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practical material that could be both the appropriate thickness and
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simultaneously durable would be sheet metal. The Dreamcast SD's serial connector
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uses 0.3mm aluminum sheet metal.
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After re-creating a technical diagram for the reverse-engineered dimensions of
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the serial connector's shield, I was correctly informed by rapid prototyping
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factories that this type of sheet metal bending/tolerance requires a mold, and
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the minimum order quantity would be somewhere around 10,000 units.
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I don't think I can sell 10,000 units, so the idea seems too risky.
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I then redesigned my 3D model to be appropriate for SLM 3D-printing. Compared to
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sheet metal, printed metal is significantly more brittle. To counter this, the
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shield needs to be thickened and reinforced significantly to prevent cracking
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and excessive fragility.
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I decided given the overall maximum outer dimensions of the connector, the
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placement and size of the conductive pins, and the consequences this would have
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on the durability of the interior plastic, that the maximum shield thickness
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would would be around 0.7mm.
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This thickening has a further compromise, in that 0.7mm will not fit in the
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≤0.5mm gap inside the Dreamcast serial connector. Taking inspiration from the
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RetroOnyx SLS 3d-printed connector, I decided it would be acceptable to remove
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that area of the shield entirely.
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After ordering SLM 3d-printed aluminum shields for a fit test, I found the
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results simultaneously impressive and disappointing.
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- the outer dimensions, particularly after light sanding, are far superior to
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the Dreamcast SD connector tolerances
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- my slightly-corrected detent-receptacle positioning appears to be perfect; the
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connector mates with a Dreamcast with a satisfying "snap" feeling.
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- I don't know exactly what happened, but during assembly testing at the rapid
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prototyping factory, the shields were about 0.5mm too long. The factory then
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corrected this by grinding the parts by hand. This grinding was not done
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carefully, and many parts are visibly no longer square as a result.
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Most importantly, SLM-printed aluminum (and aluminum in general) very strongly
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resists naive attempts to plate it with tin. In my discussions with factories, I
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was surprised to learn that they apparently have never tried to make custom
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connectors like this, and don't formally support any surfacing options that
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would be explicitly usable for soldering.
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This causes two problems:
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- the solder joint between the PCB and the connector shield is the primary means
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that the connector is mechanically joined with the PCB
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- not being able to provide a solid electrically-conductive path from the ground
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plane of the PCB and the shield causes the shield to lose some of its "shield"
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properties.
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After thinking about this for many days, I decided that it would be "ok" to join
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the connector to the PCB with a precise application of (non-conductive) glue, if
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I were not able to find a factory able to provide tin-plated 3d-printed aluminum
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(or an equivalent surfacing option that makes the part usable for soldering).
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The next issue is in price:
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- the factories are able to provide fairly nice laser cut conductive pins, but
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these are still very expensive: about $1-2 per pin, depending on
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material/surfacing. I could "save" up to $4 per connector by simply not
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installing the unused 5V and 3.3V pins, but this feels "too cheap" for me to
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be comfortable with.
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- overall, the material cost for a rapid-prototyped Dreamcast serial connector
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appears to be around $21 to $31 USD.
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I personally think these are quite nice, but I doubt most people think the
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"satisfyingly tactile snap" is worth +$31 USD to the cost of a Dreamcast
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USB-UART adapter.
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The next option is to look at higher-volume production. This would mean
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commissioning:
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- molds for sheet metal bending for the shield
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- molds for injection molding for the pin guides
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- cutting stamps for the conductive pins
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All of these have minimum order quantities around 1,000-10,000 units. The goal
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would be to get the price of the connector down to somewhere on the order of
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$2-$4/each at 10,000 units.
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Is it just me, or is anyone else interested in crowdfunding "a better Dreamcast
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serial connector" into existence?
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